AN ABSTRACT OF THE THESIS OF
Tariq A. AL-Sabbagh for the degree of Masters of Science in
Animal Science presented on June 21,1994.
Title: The Relationship of Prepartum Body Condition Score To
Postpartum Colostrum Ouality And Milk Yield And Composition
in Polypay Sheep.
Abstract approved.
Redacted for Privacy
Lloyd Swanson
Two experiments were conducted at the OSU Sheep Center
to examine the effect of body condition score at lambing
(BCSL) on immunoglobulin concentrations (IgG), milk yield
and composition and lamb performance.
The experiments used
Polypay ewes, 4 to 7 years of age, one-half mated to Polypay
rams and one-half mated to Columbia rams.
adjusted to two lambs shortly after birth.
Litters were
Milk yield was
determined by hand milking, aided by oxytocin.
Data were
analyzed using least squares analysis of variance.
In the first experiment, 101 ewes were divided into
three groups at lambing, based on their BCSL (2.5, 3.0,
3.5).
Colostrum samples were collected by hand milking from
each ewe within 11 hr of lambing and IgG concentrations were
determined using radial immunodiffusion.
Colostral IgG
averaged 57 ± 2.3 mg/ml and decreased significantly with
time.
The estimated IgG at parturition (time 0) was 76
mg/ml and linear regression analysis predicted that IgG
would decline to 0 at 23 hr postpartum.
Colostral IgG
concentrations were not affected by BCSL, age of ewe, breed
of mating sire or birth rank.
Lamb mortality through
weaning was 17.6% and was not influenced by BCSL, age of
ewe, breed of mating sire, sex of lamb, or birth rank.
Total weaning weights of lambs was 58.5 ± 1.38 kg and was
not affected by BCSL.
Total weaning weights were the lowest
in 7-yr-old ewes (31.7 ± 3.50 kg) and the heaviest in 6-yrold ewes (53.1 ± 2.56 kg).
Total weaning weights were
greater in lambs sired by Polypay rams (50.0 ± 2.03 kg) than
in lambs sired by Columbia rams (38.0 ± 2.17 kg).
The second experiment used 43 ewes, selected from the
first experiment, that had BCSL of either 2.5 or 3.5.
Body
condition scores, milk yield and composition, and lamb
weights were obtained at three 28 day intervals beginning at
27 ± 4 days after lambing.
Body condition score decreased
significantly (24%) in the high BCSL group (3.5) during the
first month after lambing but only decreased by 1.6% in the
low BCSL group (2.5).
Thereafter, the two groups plateaued
during the second month and then increased significantly
during the third month, yielding a quadratic response.
The
4-yr-old ewes were the lowest in BCS each month and ewes
giving birth to twins had higher BCS's than ewes having
multiple lambs (3).
Milk yield declined linearly from
3,260 ± 342 ml at the first month to 1,571 ± 193 ml at the
third month.
Milk yield was not affected by BCSL or other
parameters.
Percent milkfat declined curvilinearly from
11.71 ± 0.481% at the first month to 8.67 ± 0.526% at the
third month and was not affected by BCSL.
Percent milk
protein increased in a quadratic fashion from 4.02 ± 0.068%
at the first month to 5.25 + 0.082% at the third month.
It
was higher (P<0.05) in the low BCSL group at the second
month and in 7-yr-old ewes during the entire lactation.
Percent milk protein was always higher in ewes giving birth
to twins, particularly at the third month (P<0.05), and in
ewes mated to Polypay rams.
Lamb birth weight and growth
from birth to weaning were not affected by BCSL.
Lamb
weights were always the highest at each month for 7-yr-old
ewes and purebred lambs were always heavier than crossbred
lambs.
Twin female lambs were heavier than twin male lambs,
although twin male lambs gained weight more rapidly after
the second month.
It is concluded that BCSL, over the range
studied, is not an important factor affecting performance of
ewes or their lambs during lactation.
The Relationship of Prepartum Body Condition
Score to Postpartum Colostrum Quality and
Milk Yield and Composition in
Polypay Sheep
by
Tariq Ashour AL Sabbagh
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Master of Science
Completed June 21, 1994
Commencement June 1995
APPROVED:
Redacted for Privacy
Professor of Animal Science in charge of major
Redacted for Privacy
Head of Department of Animal Science
Redacted for Privacy
Dean of Graduate School
Date thesis is presented
June 21, 1994
Typed by researcher for
Tariq Ashour AL Sabbagh
TABLE OF CONTENTS
CHAPTER 1.
INTRODUCTION
1
CHAPTER 2.
LITERATURE REVIEW
4
Body condition score as an
estimator of nutritional status
Effect of body condition score
Colostral IgG concentration
Factors affecting milk production
and composition
.
.
.
.
.
CHAPTER 3.
EXPERIMENTAL PROCEDURE
Body condition score at lambing
Ewe management
Lamb management
Colostrum collection
Milking process
Analysis of milk composition
.
.
.
Analysis of colostral IgG
concentration
Data analysis
19
19
20
21
21
23
24
25
RESULTS
31
Colostrum Experiment
31
Colostral IgG
Lamb mortality
Weaning weight
31
32
32
Lactation Experiment
Body condition score
Daily milk yield
Milk composition (fat & protein)
Lamb weight
CHAPTER 5.
7
10
12
17
(fat & protein)
CHAPTER 4.
4
33
.
33
35
36
37
DISCUSSION
58
Colostrum Experiment
58
Colostrum
Lamb Mortality
Lactation Experiment
Body Condition Score
Milk Yield
Milk Composition
58
60
62
62
64
69
Table of Content, Continued
Lamb Weights
Conclusion
BIBLIOGRAPHY
72
75
76
LIST OF FIGURES
Figure
Page
1
Linear regression curve for sheep
immunoglobulin (IgG) concentrations using
radial immunodiffusion (Exp. 1).
29
2
Linear regression of ewe colostrum
immunoglobulin(IgG) concentrations
on time of collection after parturition
50
(Exp. 1).
3
Least square means of body condition score
during lactation of ewes of different body
condition scores at lambing (BCSL) and of
different birth rank at lambing (Exp. 2).
4
Least square means of body condition score
during lactation of ewes of different ages
at parturition (Exp. 2).
52
5
Linear regression of least square means of
daily milk yield of ewes of different body
condition score at lambing (BCSL)(Exp. 2).
52
6
Linear regression of actual daily milk yield
of ewes of different body condition score at
lambing (BCSL) (Exp. 2).
7
Least square means of percent fat and protein
in milk during lactation of ewes of different
body condition score at lambing (BCSL) (Exp. 2).
8
Least square means of total lamb weight during
lactation of ewes of different body condition
score at lambing (BCSL) (Exp. 2).
.
.
.
.
.
.
.
.
.
.
.
.
50
54
54
56
LIST OF TABLES
Table
Page
1
Classification of ewes involved in the colostrum
(n= 101) and lactation (n= 43) studies.
2
Least square means of colostral immunoglobulin
(IgG) concentrations and total weaning weight
of lambs (0,1,2) at 95 days of age as affected
by body condition score at lambing (BCSL), age
of ewe, mating sire and birth rank.
3
Lamb mortality classified by body condition score
at lambing (BCSL), age of ewe, mating sire, sex of
lambs and birth rank.
4
Least square means of body condition score as
affected by body condition score at lambing (BCSL),
age of ewe, birth rank, mating sire and sex of
suckling (twin) lambs.
5
Least square means of milk yield (ml) as affected
by body condition score at lambing (BCSL), age of
ewe, birth rank, mating sire and sex of suckling
.
.
.
.
.
.
.
.
.
.
.
28
40
41
42
43
.
(twin) lambs.
6
Least square means of percent fat in milk as
affected by body condition score at lambing (BCSL),
age of ewe, birth rank, mating sire and sex of
suckling (twin) lambs.
7
Least square means of percent protein in milk
as affected by body condition score at lambing
(BCSL), age of ewe, birth rank, mating sire and
sex of suckling (twin) lambs.
8
Least square means of total weight born (twin lambs)
as affected by body condition score at lambing (BCSL),
age of ewe, birth rank, mating sire and sex of
suckling (twin) lambs.
46
9
Least square means of total lamb weights' (kg)
at 30, 60 and 90 days postpartum and at weaning
(95 days) as affected by body condition score
at lambing (BCSL), age of ewe, birth rank, mating
sire and sex of suckling (twin) lambs.
47
10
Correlation coefficients for ewe and lamb
characteristics (Exp. 1).
.
44
.
.
.
.
.
45
48
List of Tables, Continued
11
Correlation coefficients of some ewe and lamb
characteristics during lactation (Exp. 2).
.
.
49
The Relationship Of Prepartum Body Condition Score
To Postpartum Colostrum Quality And Milk Yield And
Composition in Polypay Sheep.
CHAPTER 1.
INTRODUCTION
Great Britain and some parts of Europe such as France
and Romania are important and famous areas in the sheep
industry.
These areas are rich in natural resources and
enjoy environments conducive to the success of the sheep
industry.
In the Middle East, however, sheep raising is
challenging because of the scarcity of natural resources
Yet, the sheep industry remains vital to the Middle East for
the following reasons: 1) sheep are sociologically important
because they are a source of wealth and respect in this
society, thus people prefer meat from sheep as compared to
other species,
2) sheep are easier to raise than other
grazing animals in an environment which has insufficient
natural resources (water and forage), and 3) sheep are
important to the religion and customs of the Middle Eastern
people.
In religious ceremonies such as Hajj and Eid, the
demand for sheep increases many times.
Millions of sheep
are slaughtered at these festivals to share with the poor.
The need for sheep for the religious festivals cannot be met
by the domestic supply, especially in Saudi Arabia, the Hajj
location.
As a result, all of the live sheep exported from
New Zealand are shipped to Saudi Arabia (Storey & Sri
Ramaratnam, 1991).
In addition, the milk of ewes is high in
2
fat, which makes it unique and preferred in the Middle East.
These people use the milk to produce dairy products, such as
cheese and yogurt and use the wool for clothes; even the
skin may be used to make musical drums. For these reasons
the sheep industry is very important in the Middle East.
The socio-economic importance of sheep creates the need
to discover the factors which affect their productivity.
Scientists have examined the various aspects of sheep
husbandry to maximize their benefits while minimizing costs.
One area which has been studied closely is the relationship
of body condition score to performance of sheep.
After a gestation period of about 145 days the pregnant
ewe gives birth to single, twins, triplets and occasionally
quadruplets and quintuplets.
suckled by newborn lambs.
Colostrum is the first milk
Colostrum is high in
immunoglobulin, particularly immunoglobulin G (IgG), which
provides passive immunity to the newborn lambs; the level of
passive immunity attained is proportional to the
concentration and quantity of immunoglobulin and the time
interval after birth in which the colostrum is consumed
(Esser et al., 1989).
During the nursing period, lambs
derive most of their nutrients for growth from the ewe's
milk.
The nursing period
the time interval from birth to
weaning -varies in length from about 6 to 13 weeks.
Generally, the shorter the nursing period the lower the
3
growth rate and the higher the post weaning mortality rate
(Fogarty et al., 1992).
Thus, milk production is very important to lamb growth.
Therefore, it is important to gain more information about
factors that affect milk production. Body condition scoring,
which reflects the nutritional status of the ewe, may be an
important factor affecting milk yield.
This study was designed to provide information on the
relationship of prepartum ewe body condition score and
postpartum colostrum quality and milk yield and composition.
4
CHAPTER 2
LITERATURE REVIEW
Sheep are one of many resources used by man.
Sheep
have the ability to convert low quality food sources from
plants into such products as milk, meat, animal oil and
wool.
The desire for these commodities has created a
proliferation of scientific research to develop methods that
maximize the ratio of benefits to cost in raising sheep.
Numerous studies have investigated ways to measure and
enhance sheep performance and productivity.
Productivity of sheep can be measured by litter size,
number of lambs weaned per ewe,
(Sidwell and Miller, 1971;
Dickerson and Glimp, 1975; More-O'Ferral, 1976; Parker and
Pope, 1983; Lewis and Burfening, 1988) and the nutritional
status of ewes and lambs (Jordan and Mayer, 1989).
Body Condition Score As an Estimator of Nutritional Status
Body condition score (BCS) and live weight are two
systems for measuring nutritional status in ewes.
Body
condition score, the assessment of fat and muscle in the
loin region, is a system which estimates the degree of
muscling and fat development in an animal (Russel et al.,
1969; Ducker and Boyd, 1977).
It is considered to be a more
subjective, accurate and inexpensive estimator of a ewe's
nutritional status than body weight because skeletal size
5
adds to the live weight without being a determinant of the
nutritional status. Fat stored in the body becomes a
reservoir for energy.
Pregnancy, lactation and
undernourishment, for example, would be a time when an
animal utilizes this fat reserve.
Body condition score is a
better predictor of fertility and total fat deposits in the
animal than body weight (Barth and Neumann, 1991).
The regression of BCS on body weight is curvilinear;
the change in body weight increases at an increasing rate as
BCS increases from 1 to 5 (Teixeira et al., 1989).
Body
condition scoring was developed by Jefferies (1961), using a
scale of one to five, where 1=thin and 5=obese.
al.
Russel et
(1969) refined the system by adding half point
gradations.
The procedure for scoring the condition of an
animal's body is done tactically in the loin area, assessing
the degree of muscle and fat that surround the vertebrae.
This area is optimal in that it is the first part of the
body to be covered with fat and muscle and the last area to
lose it.
Also, subcutaneous fat correlates more closely
with percentage of total body fat than does the
intermuscular, mesenteric or perirenal fat (Russel et al.,
1971; Greg, 1974).
This system has proven to be useful and is reasonably
repeatable.
Oriordan and Murphy (1987) observed that 370 of
the scores were repeatable when they used this system for
determining the body condition of 54 pregnant ewes.
Ninety-
6
five percent of the remaining scores were within 0.5 units,
and no animal had scores differing by more than 1.0 unit,
giving credence to the repeatability of this technique.
Although BCS has a lower repeatability than live
weight, it correlates more closely with percent body fat.
Of two ewes with the same skeletal size but with a BCS
differing by 1 unit, the ewe with the higher BCS was 10 kg
heavier (Russel et al., 1969).
Body condition scoring is also used for other species,
for example, a scale of 1 to 5
(Meinert et al., 1992;
Perkins et al., 1985; Edmonson et al., 1989; Ruegg et al.,
1992) or 1 to 10 (Northcutt et al., 1992) is used to score
dairy and beef cattle.
In dairy cattle, 1 unit of BCS is
equivalent to 545.5 kg milk.
The goal for commercial ewes, sold for meat purposes,
is a body condition score of 3.0, in which fat represents
301; of the weight of a fleece-free carcass.
The primary factor affecting BCS is dry matter intake,
which is influenced by the age and breed of sheep (Bocquier
et al., 1987).
However, dry matter intake decreases in ewes
with BCS of a 4 (Trabalza-Marinucci et al., 1992).
A BCS a 3.0 is important for embryonic development
during early pregnancy, resulting in lower prenatal
mortality (Alexander, 1964; Nordby et al., 1986).
At mid
gestation a BCS a 3.0 is necessary for optimal placental
growth (Mellor, 1990).
The most crucial period is late
7
pregnancy (90 days to parturition) when the greatest fetal
growth occurs (Robinson et al., 1977; Mellor, 1990).
Effects of Body Condition Score
Body condition score has been studied to observe its
effect on ewe reproductive performance.
Rhind and
Schanbacher (1991) studied the effect of BCS on the
reproductive performance of crossbred ewes.
Ewes with a
high BCS had larger follicles than ewes with a low BCS
during the luteal and follicular phases of the estrous
cycle.
However, BCS had no effect on the number of
follicles.
Generally, reproductive performance improved
when BCS ranged from 2.25 to 2.50.
After ewes attained a
BCS of 2.50, some breeds continued to improve in
reproductive performance (Welsh Mountain) while reproductive
performance declined in other breeds (Gunn et al., 1991).
Coop and Clark (1969), Gunn et al.
Doney (1979), Rhind et al.
(1969), Gunn and
(1984a,b), and Meyer (1985)
observed a positive correlation between BCS and mean
ovulation rate, although Rhind et al. (1991a) failed to
observe this correlation in a small study using Greyface
ewes.
The BCS had no significant effect on luteinizing
hormone (LH) and follicle stimulating hormone (FSH)
concentrations (Rhind et al., 1984a) and pulse amplitude of
8
LH during the estrus cycle (Rhind and Schanbacher, 1991).
Two days after ovariectomy, ewes with a high BCS had a
higher mean LH pulse frequency and higher FSH concentrations
(Rhind et al., 1991b; Rhind and Schanbacher, 1991).
Body
condition score directly affected hypothalamic activity and
gonadotropin releasing hormone (GnRH) secretion but not
pituitary sensitivity to GnRH (Rhind et al., 1991b).
Rhind et al.
(1991c) repeated a study using 37 ewes,
varying from a high BCS (3.50) to moderate BCS (2.50 to
2.75).
No significant differences in pregnancy rate, ova
wastage rate and profiles of progesterone and prolactin were
observed, although ewes with a lower BCS tended to have
lower prolactin levels (Rhind et al., 1991b).
Body
condition score did not affect progesterone levels following
exogenous LH pulses (Rhind et al., 1991b).
Unlike the
previous findings, the conception rate was slightly higher
in ewes with a high BCS (Wallace, 1961; Coop, 1962; Taplin
and Everitt, 1964; Coop, 1966; Meyer and Bradford, 1973;
Nordby et al., 1986; Gunn et al., 1990; West et al., 1991).
While some studies have concluded that embryonic
survival was not affected by changes in BCS (Rhind et al.,
1984a), most studies have shown a positive correlation
between BCS and embryonic survival (Guerra et al., 1971;
Gunn et al., 1972; Gunn and Doney, 1975, 1979; Cumming et
al., 1975; Gunn and Maxwell, 1989; West et al., 1991).
9
Ewes with a higher BCS tended to have greater lamb
survival (Johnson et al., 1982; Sykes, 1982; BerggrenThomas, 1984; Jordan and Feuvre, 1989; Nawaz et al., 1992;
Nawaz and Meyer, 1992; King et al., 1990).
Jordan and Hanke
(1991) failed to observe a positive correlation between ewes
with a high BCS and lamb survival but their experiment was
conducted on ewes with a high mean BCS which produced a
higher quality and quantity of milk for their lambs.
Lamb
birth weight and lamb survival were positively correlated
with a high BCS at late gestation (Alexander, 1964;
Robinson, 1983; Beeston, 1984; Scales et al., 1986; Jordan
and Mayer, 1989; Hohenboken et al., 1988) due to reduced
prenatal growth in ewes with low BCS (Rattray et al., 1974;
Mellor and Murray, 1981, 1982). A low plane of nutrition in
ewes during the last six weeks of gestation resulted in low
birth weight lambs (Treacher, 1971).
However, other studies
have shown no effect of BCS on birth weight of lambs (Slade,
1980; Jordan and Hanke, 1991; Gunn et al., 1986).
The lack
of differences in these latter studies, however, may have
been due to the small range in BCS's in these ewes.
The growth rate of the lambs, which is dependent on
milk yield, was not affected by differences in the BCS of
their dams in late gestation (Slade, 1980; Gibb and
Treacher, 1982; Jordan and Hanke, 1991).
However, Treacher
(1971), Gibb and Treacher (1980), Rhind et al.
Aguilera et al.
(1992) and
(1992) reported that ewes with a lower BCS
10
during late gestation had decreased milk production when a
restricted diet was fed after parturition.
Molina et al.
(1991), on the other hand, reported that ewes with a higher
BCS weaned heavier lambs.
The onset of anestrus occurred 51 to 75 days earlier in
ewes with low BCS (Forcada et al., 1990).
Not only did ewes
with a high BCS exhibit a higher incidence of estrus, they
also exhibited greater ovarian activity, greater number of
corpora lutea (Forcada et al., 1990), and increased litter
size (Burditt et al., 1987).
Colostral IgG Concentrations
Colostrum is the first milk produced by the ewe after
parturition.
It is rich in immunoglobulins which are
important for passive immunity of the lambs.
The level of
passive immunity is proportional to the concentration of
immunoglobulin in colostrum and the quantity of colostrum
ingested (Esser et al., 1989).
Immunoglobulin G (IgG) is
one of the five classes of humoral antibodies produced by
the body in response to invasions by bacteria, fungi and
viruses.
The concentration of IgG is usually determined using
the radioimmunodiffusion (RID) method developed by Mancini
et al.,
(1965) and modified by Fahey and McKelvey (1965).
Colostrum quality can also be determined by enzyme-linked
11
immunosorbant assay (ELISA) or radioimmunoassay (RIA), that
are extremely precise, or less precisely by specific gravity
(Toenjes et al., 1991).
In general, the RID method is
simple and requires a minimal investment in equipment (Check
and Piper, 1986).
There is no significant relationship
between the appearance or color of colostrum and its
concentration of immunoglobulins.
Toenjes et al.
(1991) observed a small but negative
relationship between the interval from calving to first
milking and immunoglobulin content.
The quantity of
colostrum was positively related to the colostral IgG
production (Esser et al., 1989; Shubber et al., 1979).
The
age and genotype of the ewe, BCS, litter size, and sex of
the lambs had no significant effect on colostral IgG
concentration (Esser et al., 1989) or colostrum yield
(Thomas et al., 1988).
On the other hand, Gilbert et al.
(1988) observed higher IgG concentrations in yearling ewes
than in older ewes.
Colostrum production was lower for single-bearing than
for twin-bearing ewes (Gallo and Davies, 1987).
Ewes
delivering triplets had higher protein and immunoglobulin
concentrations in their colostrum than ewes delivering twins
(Gallo and Davies, 1987; Gilbert et al.,1988).
12
Factors Affecting Milk Production and Composition
Newborn lambs depend on milk for most of their early
nutrition.
Quality and quantity of milk consumed during the
first weeks of life are important determinants of both
health and growth of lambs (Brown and Hogue, 1985).
Therefore, factors that affect milk yield and composition,
such as nutrition, lactation stage, diet, and age and breed
become important to lamb survival.
Milk yield can be measured by hand milking, machine
milking and lamb-suckle-weigh methods.
Studies show that
the hand milking and machine milking techniques yield
similar results (Papachristoforou, 1990).
The lamb-suckle-
weigh method is not as reliable as the hand or machine
milking methods because it depends on the lamb's appetite
(Peart, 1967).
Doney et al.
(1979), however, found that
hand or machine milking agreed well with the lamb-suckleweigh method.
Milk production begins immediately after parturition,
peaks at 2 to 4 weeks postpartum, and then declines (Peart,
1967, 1968, 1970; Wohlt et al., 1984; Brown et al., 1987;
Reynolds and Brown, 1991).
Peart (1967) observed that milk
yield decreased from 2.91 L/day during the third week of
lactation to about 0.87 L/day during the tenth week of
lactation.
During the lactation period, milk composition
averaged 5.5% protein and 6.2% fat (Boylan and Sakul, 1988;
13
Banda, 1992).
Percentage of fat in milk used to be
determined using the Babcock method.
The Babcock method
involves the use of a strong acid, making it hazardous to
Therefore, the infrared method (IR)
use.
is currently
widely used to determine the percentages of fat and protein
in milk; it is based on the absorption of IR energy at a
specific wave length by carbonyl groups in ester linkages of
the fat molecule and by peptide linkages between amino acids
of protein molecules.
Dorset, Finnsheep, Lincoln,
Rambouillet, Ramonov, Suffolk and Targhee ewes were tested
for milk production and composition (Sakul and Boylan,
1992).
Suffolk's had the highest milk yield while Ramonov's
had the lowest milk yield.
Milk of the Finn breeds was the
lowest in protein content.
Bass (1989) failed to detect a
difference in milk yield between the Scottish Black Face and
East Friesland breeds.
Generally, milk production was lower
in American breeds than in the "dairy" sheep breeds of
Europe and the Middle East (Reynolds and Brown, 1991).
Snowder and Glimp (1991) failed to detect differences in
milk yield between the Rambouillet, Columbia, Polypay and
Suffolk breeds.
Cross breeding was an effective means to increase milk
yield but not necessarily milk composition (Sakul and
Boylan, 1992).
Milk fat and protein were unaffected by the
number of suckling lambs (Snowder and Glimp, 1991) but
increased when low roughage diets (high energy) were
14
introduced (Brown and Hogue, 1985).
Milk protein
concentrations were higher when ewes were fed on a high
plane of nutrition (Barnicoat et al., 1965) or when diets
were supplemented with fish meal (Penning et al., 1988).
Dorset's and Ramonov's produced milk with the highest
protein content while the Finn breed was the lowest in
protein content.
Milk yield was affected by stage of
lactation; it peaked at the third to fourth week and
declined gradually during the remainder of the lactation (AL
Saiegh and AL Khauzai, 1993).
Each 2.3 kg of milk resulted in 0.45 kg of lamb gain
(Robinson and Forbes, 1968).
Part of the decline in milk
production can be attributed to the decreased suckling
stimulus as lambs begin supplementing their diets with other
feeds (Wohlt et al., 1984; Reynolds and Brown, 1991),
resulting in a positive correlation between milk yield and
average daily gain in lambs during early lactation (Peart,
1967).
Body weight of ewes and lamb birth weight, along
with daily lamb weight gain during the different periods of
lactation, correlated with milk yield (AL Saiegh and AL
Khauzai, 1993)
.
Nutrition is the primary factor affecting milk yield
(Barnicoat et al., 1949).
Milk yield was positively
correlated with feed consumption at the eighth week of
lactation (Barnicoat et al., 1949;
1991).
Reynolds and Brown,
The quality of the diet affected milk yield as well.
15
When feed was restricted after lambing, ewes with a higher
BCS had higher milk yields than ewes with a lower BCS
(Peart, 1970; Russel et al., 1977), although this difference
disappeared when the ewes were fed to requirement (Peart,
1967, 1968).
Low dietary protein during the last six weeks
of gestation led to a lower milk yield after parturition
(Wallace, 1948a; Slen and Whiting, 1952; Bass, 1989).
Accessibility to water also affected milk yield.
Ewes
watered every 24 hr produced more milk than ewes watered
every 48 or 72 hr (Aganga et al., 1988).
A decrease in the
watering interval also resulted in a significant increase in
fat and protein concentrations (Aganga et al., 1988).
Milk yield is also influenced by the number of suckling
lambs (suckling stimulus).
Ewes nursing single lambs had
lower milk yield in late lactation than ewes nursing twins
(Wallace, 1948a,b; Doney and Munro, 1961; Robinson and
Forbes, 1968; Ricketts, 1970; Joseph and Foot, 1980; Torres-
Hernandez and Hohenboken, 1980; Hinch et al., 1983; Thomas
et al., 1988; McMillan et al., 1988; Bass, 1989; Dove and
Milne, 1991; Snowder and Glimp, 1991; Peeters et al., 1992;
Rhind et al., 1992).
Milk yield was affected by the
adjusted number of suckling lambs during the lactation
period, regardless of the actual number of lambs born (Rhind
and Schanbacher, 1991).
Fecht and Boylan (1987) and
Reynolds and Brown (1991), however, failed to detect
16
differences in milk yield between ewes nursing single or
twin lambs.
(n=24)
This might be a result of a small sample size
.
Suckled milk yield was correlated positively with udder
width at peak lactation (r=0.66) and with ewe body weight
(r=0.75) at breeding (Reynolds and Brown, 1991).
Generally,
larger udders produce more milk than smaller ones (Linzell,
1966; Davis et al., 1980; Reynolds and Brown, 1991).
Milk yield decreased significantly after ewes attained
4.5 years of age.
Peeters et al.
(1992) observed that two-
year-old ewes produced more milk than one-year-old West ewes
of the European breed.
Ewes with high milk production
during early lactation continued high performance of milk
yield at 45 days postpartum.
17
CHAPTER 3
EXPERIMENTAL PROCEDURE
Two experiments were conducted at the Oregon State
University Sheep Research Center during the 1993 lambing
season (February
March) using 104 Polypay ewes.
One-half
of these ewes were mated to rams of the Columbia breed and
the other half were mated to rams of the Polypay breed. The
experiments were conducted to determine the effect of body
condition score at lambing (BCSL) to colostral IgG quality
(Exp. 1) and the effect of BCSL on body condition score
(BCS), milk yield, percentages of fat and protein in the
milk and weight gain of lambs at selected intervals during
lactation (30, 60 and 90 days postpartum) and at weaning (95
days postpartum)(Exp.2).
In Experiment 1 we were only able to collect colostrum
samples from 101 of the 104 ewes because a snowstorm
prevented access to the Sheep Research Center within 12 hr
of lambing for 3 of the ewes.
Table 1 illustrates how the
101 ewes were allocated when classified according to BCSL,
age of ewe at lambing, breed of sire and number of lambs
born (birth rank).
All of the ewes were within a BCSL range
of 2.5 to 3.5 and varied in age from 4 to 7 yr.
The
majority of ewes (55%) had twin lambs at parturition, 8% had
singles and the remaining 37% had 3 to 5 lambs at
parturition (R = 3.4 lambs).
Within 2 hr of lambing, the
litters of ewes with more than 2 live lambs were reduced to
18
two lambs of similar bodyweight, regardless of sex, to nurse
each ewe (hereafter referred to as adjusted lambs).
Forty-three ewes were selected from the colostrum
experiment for the lactation study (Experiment 2)(Table 1).
One ewe was dropped after the first month of lactation when
she developed mastitis and two additional ewes were dropped
after the second month of lactation; one died of natural
causes and one had a severe teat injury which precluded
suckling or hand milking.
To allow for maximum detection of
differences due to BCS, only ewes with the BCS extremes (2.5
or 3.5) were used.
Due to a shortage of ewes with a BCS of
3.5, only 16 of the 43 ewes had a BCS of 3.5.
The ages of
the ewes ranged from 4 to 7 yr; most (46.5%) were 6 years of
age and in their fifth season of lambing.
Since all ewes
were adjusted to nurse two lambs during lactation, ewes
lambing with singles were deleted from the lactation study.
Forty percent of the ewes gave birth to three to five lambs
which were subsequently adjusted to two lambs.
Slightly
more than one-third (370) of the ewes nursed two lambs of
the same sex (an equal number of ewes nursed two males or
two females) and the remainder nursed one lamb of each sex
(Table 1).
19
Body Condition Score at Lambing
Ewes (n=104) were scored weekly for body condition
beginning three weeks before lambing and continuing until
all ewes had lambed.
The last BCS prior to parturition was
considered to be the BCSL.
The ewes were scored
individually by the same person to decrease variability in
scoring.
The scoring system was based on a 5 point scale
with half-point gradations where 1 is very thin and 5 is
obese (Russel et al., 1977).
This system is based on
determining the degree of sharpness of the spinous and
transverse processes in the lumbar region by palpation
(Jefferies, 1961).
The procedure of body condition scoring can be
summarized in three steps.
The first step is to palpate the
degree of prominence of the spinous process in the loin
region using the thumb.
The second step is to palpate the
degree of sharpness of the transverse process in the loin
region, using the tips of the fingers for palpation.
Finally, the tips of the fingers are used to palpate the
depth of muscle and fat in the loin region.
Ewe Management
During early pregnancy the ewes were grazed on a mixed
grass-clover pasture.
At two weeks prior to lambing, the
20
ewes were moved to the lambing barn where they were given
0.91 kg rolled corn daily and grass-clover hay to appetite.
Immediately after lambing, each ewe and her lambs were moved
to a 1.75 m2 enclosure for that and the following day to
ensure bonding.
Here the ewes received a ration of alfalfa
pellets to appetite.
On the second day after lambing and
after dams were checked for mastitis (using the California
Mastitis Test), ewes and lambs were returned to group pens
where they again received a ration of 0.91 kg rolled corn
daily and grass-clover hay to appetite.
After all ewes had
lambed, they were returned to a mixed grass-clover pasture.
The ewes had been bred in late September and lambed within a
three week period in February and lambs were weaned in May.
Lamb management
Within 2-3 hr of lambing, the lambs were checked for
entropion (turned in eyelid) and navels were dipped in a
solution of 7% iodine.
Within 8-16 hr of lambing, lambs
were docked using an elastrator band, weighed, tattooed, ear
tagged, vaccinated with IBR\PI3 (Infectious Bovine
Rhinotracheitis\Parainfluenza Type 3) and male lambs were
castrated with an elastrator band. Lambs were vaccinated for
Soremouth and Enterotoxemia (Clostridium perfringens type C
& D) twice; at 7-10 d and at 3-4 wk postpartum.
21
Colostrum Collection
Colostrum samples (30 ml
approximately 15 ml from
each one-half of the udder) were obtained from each ewe by
hand milking within 12 hr of lambing.
The concentration of
immunoglobulin is known to sharply diminish after that time
(Shubber et al., 1979).
sampling was recorded.
The time interval from lambing to
The colostrum samples were stored at
-4 °C for subsequent analysis of colostral IgG
concentration.
Milking Process
Since all ewes had lambed within a three week period of
time, the 43 ewes were arranged into three milking groups to
overcome the difficulty of hand milking 43 ewes within one
day.
Each milking group consisted of ewes that had lambed
within a 7-day time period.
The first milking was centered
at 27 ± 4 days postpartum and the second and third milkings
at 28-day intervals thereafter (55 ± 4 and 83 ± 4 days.
For
convenience these will be referred to as 30, 60 and 90 days.
On the day of milking, the ewes and lambs were moved to a
barn where the lambs were weighed and the ewes were body
condition scored by the same individual as previously.
The
ewes were physically separated from their lambs but within
sight and sound of each other. The ewes were individually
22
moved to an elevated platform for hand milking.
Oxytocin (5
IU) was administered intramuscularly (im) in the rear leg
(McCance, 1959).
Although oxytocin is often administered
intravenously, Geenty (1980) found that it was just as
effective when administered intramuscularly.
The ewes were
hand milked until all milk had been removed, and a second
injection of oxytocin (5 IU,
im) was administered.
After a
2 min wait the ewes were hand milked again and the milk was
discarded.
After a separation period of 3-4 hr (McCance,
1959; Thomas et al., 1988, Brown et al.,1987) which
corresponds to normal suckling intervals of lambs (Ricordeau
et al., 1960) the same hand milking procedure, utilizing two
injections of oxytocin (5 IU, im), was followed.
Milk from
the latter two milkings was combined, the volume recorded
and a sample taken for fat, protein and somatic cell
determination.
Milk volume was later corrected to 24 hr
secretion, assuming that milk synthesis was similar during
the entire 24 hr as was determined for the 3-4 hr separation
time.
Following milking, the ewes and their lambs were
returned to pasture.
The same milking procedure was
followed at 60 and 90 days.
Hand milking, using the oxytocin-induced method
(McCance, 1959; Wohlt et al., 1984; Reynolds and Brown,
1991; Holcombe and Hallford, 1988), was employed rather than
the traditional lamb-suckle-weigh method because of greater
accuracy for the determination of milk yield.
The lamb-
23
suckle-weigh method varies with appetite of the lambs
(Peart, 1967) and urination or defecation by the lambs
during the suckling period.
Analysis of milk composition (fat and protein)
Milk samples were filtered to remove debris, preserved
with Bronopal, refrigerated overnight and then sent to the
DHIA Testing Center in Salem, OR.
The samples were analyzed
for fat and protein by infrared spectroscopy (Williams,
1984; Snowder and Glimp, 1991) using a Multi Spec
spectrometer (Berwind Instrument Group, Florida), and for
somatic cell count using a Foss Model 215 (Foss America
Inc., New York).
Fat determination in sheep milk, using the
infrared spectroscopy method, differs slightly from that of
cows due to differences in the fat refractive index
(Grappin, 1986).
Results for sheep milk can be corrected
using a regression equation (Reynolds and Brown, 1991).
However, because the difference between the two readings
would not have exceeded 1.7%, the calculated milk fat
percentage was not corrected.
Similarly, the percentage of
protein in sheep milk as determined by infrared spectroscopy
differs from bovine milk due to differences in the ratio of
whey protein to true protein (Grappin, 1986).
Because this
difference did not exceed 10% in any of the samples, the
calculated protein percentage was not corrected.
24
Analysis of Colostral IgG Concentration
The IgG concentration in colostrum was analyzed using
the radioimmunodiffusion (RID) technique (Mancini, 1965;
Fahey and McKelvey, 1965).
This technique depends on
precipitation of the antibody-antigen complex around a well.
Plastic plates (10.5 x 5.5 cm) containing a 1 mm layer of
gel which incorporated antibody to sheep IgG (The Binding
Site Limited, Birmingham, England) were used.
Fourteen
wells (2 mm diameter) were distributed throughout the gel
plate.
Diluted colostrum samples or IgG standards (5 Al)
were pipetted into each well, the plates covered, and then
incubated at room temperature in a humidified atmosphere for
72 hr.
As the colostral or standard IgG (antigen) migrated
through the gel, it complexed with the antibody.
The
distance migrated was proportional to the concentration of
IgG.
When a sufficient concentration of the Ag-Ab complex
had accumulated (proportional to the concentration of
colostral IgG), it precipitated and formed a visible ring
around the well.
All colostrum samples were initially diluted 1:40 using
7% BSA in distilled water (Guidry and Pearson, 1979).
Any
colostral sample that had a precipitate ring diameter
greater than that of the high standard (25% of the samples)
was further diluted to 1:80 or 1:160.
Samples with an
indistinct precipitate ring were also reassayed.
After the
25
72 hr incubation period, the diameter of the precipitate
rings were determined using a jeweller eyepiece (7x) with a
micrometer scale inscribed on the objective.
If the
diameter of the precipitate ring of the high standard was
within 0.3 mm of 9 mm, the standard curve provided with the
RID kits was used.
If not, a standard curve utilizing the
three standards was constructed and a regression equation
was used to calculate the concentration of the unknowns,
using the square of the precipitate ring diameter as the
dependent variable (Figure 1).
Although the precipitate ring diameter of the high
standard (1,000 µg /ml) should have attained 9.0 mm, the 11
plates averaged 8.61 ± 0.06 mm, but were consistent (CV =
2.43%).
Of the 11 plates,
standards.
5 contained a complete set of
The medium (600 µg /m1) and low (100 µg /ml)
standards averaged 6.96 ± 0.04 mm and 4.27 ± 0.04 mm (n=5),
respectively, and also were consistent between plates (CV
1.75% and 2.65%, respectively).
=
Theoretically, the
precipitate ring diameter of the medium and low standards
should have achieved 7.25 and 4.13 mm, respectively.
Data Analysis
Data from experiments 1 and 2 were analyzed by least
squares analysis of variance (ANOVA) using the General
Linear Model (GLM) of the Statistical Analysis System (SAS,
26
1988).
The Student-Newman-Keuls (SNK) method was used to
determine significant differences between least squares
means (Steel and Torrie, 1960).
All main effects and their
interactions were included in the analysis.
The main
effects examined included treatment (BCSL), age of ewes,
birth rank, breed of sire and sex of lambs.
Main effects
(except treatment) and interaction terms having P>0.50 were
deleted from the final model.
Classifications with few
observations (generally less than 8) were either deleted
from the model or were combined with other classifications
to eliminate the problem of having empty cells which would
not generate least square means and standard errors.
Categorical data for lamb mortality were analyzed using
Chi-Square (Steel and Torrie, 1960).
Since IgG levels were significantly influenced by the
interval from parturition to sample collection, time of
collection was used as a covariate for the colostral IgG
analysis.
Adjusted lamb birth weights (total weight of
twin lambs born in litters s 3) were used as a covariate in
the analysis of the weaning weights of the lambs.
Since BCS, milk yield and milk composition were
measured repeatedly over time, a repeated measures ANOVA
model was used (SAS, 1988).
Polynomials were used to test
for linearity of the time trends during lactation (SAS,
1988).
Date of lambing was used as a covariate for the
analysis of BCS, milk yield and milk composition to adjust
27
for variation in parturition date.
The same procedure was
followed for the analysis of lamb weights during lactation
(30,
60,
90 and at weaning) but using adjusted lamb birth
weight as a covariate.
Pearson correlation coefficient analysis was used to
measure the degree of relationships between variables.
For
Experiment 1 these included BCSL, total weight of lambs
born, total weight of adjusted lambs born (multiple births
reduced to twins), total weight of lambs weaned, colostral
IgG concentration, time of colostral IgG collection, age of
ewes, birth rank, number of lambs turned out to pasture,
number of lambs that died within 12 hr postpartum and number
of lambs that died of natural causes from lambing to
weaning.
In the second experiment, Pearson correlation analyses
included BCSL, BCS at 30, 60 and 90 days, average daily milk
yield at 30, 60 and 90 days, percentages of milkfat and milk
protein at 30, 60 and 90 days, somatic cell count at 30, 60
and 90 days, age of ewes, birth rank, sex of nursed lambs,
total weight of adjusted lambs born and lamb weight at 30,
60 and 90 days and at weaning (95 days postpartum).
Table 1. Classification of ewes involved in the colostrum (n= 101) and lactation (n=
43) studies.
BCSL
Colostrum
Age of ewe, yr
2.5
3.0
3.5
4
38
35
28
26
20
34
5
6
Breed of Sire
Birth rank
Polypay
Columbia
1
2
i3
21
52
49
8
58
35
7
Sex of lambs
Male/
Male Female female
Lactation'
30 d PP
27
16
12
6
20
5
25
18
26
17
8
8
27
60 d PP
27
15
12
5
20
5
25
17
25
17
8
8
26
90 d PP
25
15
12
5
18
5
25
15
24
16
7
7
26
1 All ewes adjusted to twins for lactation study.
BCSL = Body condition score at lambing.
PP = Postpartum.
29
Figure 1. Linear regression curve for sheep immunoglobulin
(IgG) concentrations using radial immunodiffusion
(Exp.
1)
.
Figure 1, continued
80
N
E
E
60
=
Y = 12.1020 + 0.0622X
R2 = 0.9961
.._...-
L.
'E 40
0
a,
00
0
cy)
.g.
20
1
200
400
600
800
IgG Concentration 0.1g/rap
1000
31
CHAPTER 4
RESULTS
Colostrum Experiment
Colostral IgG
Unadjusted colostrum IgG levels averaged 57 ± 2.3 mg/ml
and ranged from a low of 14 mg/ml to a maximum of 114 mg/ml.
Collection of colostrum samples varied from 0 to 11 hr after
lambing and averaged 5.9 hr.
Colostrum IgG levels decreased
significantly with time (Figure 2, r=-0.46) and linear
regression analysis projected colostrum levels at 76 mg/ml
at parturition (time 0).
Using time of collection as a covariate and adjusting for
age of ewe (4-7 yr), breed of mating sire and birth rank
(twins vs. multiples), colostrum levels were unaffected by
BCSL (Table 2).
Sex of lambs and associated interaction
terms were deleted from the final model.
Birth ranks of 4
and 5 were combined with triplets while singles were deleted
from the final least squares model since there were only 9,
2 and 8 ewes with quadruplets, quintuplets and singles,
respectively.
Ewes which gave birth to twins had higher
(P=0.06) levels of colostrum IgG than ewes giving birth to
multiples.
The interaction of age of ewe with BCSL
approached significance (P=0.093).
32
Lamb Mortality
Total lamb mortality from birth to weaning (day 95)
averaged 17.60 (Table 3).
Natural death loss was 10.90,
including lambs which died before multiple litters were
adjusted to twins.
Of the lambs that died, the majority
(810) of lambs were dead at birth or died within 2-3 hr of
birth.
Age of ewe, BCSL, mating sire, sex of lamb, and
birth rank had no effect on total death loss, although the
effect of birth rank approached significance (P<0.10), as
death loss was greater in ewes having larger litters at
parturition.
Predator kill (mostly coyotes) totaled 6.7% from
turnout to weaning and was not affected by BCSL, age of ewe,
mating sire, sex of lamb or birth rank.
Weaning Weight
Neither birth rank and its interactions nor other
interaction terms (age of ewe x mating sire, age of ewe x
BCSL) had an influence on the model (P>0.50) and were
deleted from the final least squares analysis.
Body
condition score at lambing had no effect on total weight
weaned (P=0.28), although ewes with a BCSL of 3.0 tended to
wean more total lamb weight than ewes with a BCSL of 3.5
(P=0.13)(Table 2).
33
The oldest ewes (7 yr) weaned the lowest total lamb
weight whereas the 4- and 6-yr-old ewes weaned the highest
total lamb weight (Table 2).
Sire of the lambs was important; purebred lambs
(Polypay x Polypay) were weaned at a higher total weight
than the crossbred lambs (Columbia x Polypay)(P<0.001;
Table 2).
Lactation Experiment
Body Condition Score
Using parturition date as a covariate, the final
statistical model included all the explanatory variables
(BCSL, sex of lambs, age of ewes, mating sire and birth
rank), the interaction of BCSL with birth rank, time (30, 60
and 90 days of lactation), and the interactions of time and
the explanatory variables.
Body condition score differed significantly between the
two treatment groups (BCSL 2.5 vs 3.5) at 30 days but were
similar at 60 and 90 days of lactation (Table 4), although
the 3.5 BCSL group were consistently higher at each time
period.
The 3.5 BCSL group decreased significantly in body
condition score from lambing to the first month (24%)
whereas the 2.5 BCSL group only decreased by 1.60.
Thereafter, the two groups plateaued from 30 to 60 days and
34
then increased significantly from 60 to 90 days of lactation
(Figure 3), yielding a quadratic response (P=0.0001).
Age of ewe also had a significant effect on BCS, with
the 4-year-old ewes being the lowest at each time period
This is probably because 11 of the 12 4-year-old
(Table 4).
ewes were in the 2.5 BCSL group at lambing.
The interaction
of time and age of ewe approached significance (P=0.069),
due to the 7-year-old ewes increasing faster in BCS during
lactation than the other age groups (Figure 4).
Ewes giving birth to twins were consistently higher
(P=0.015) in BCS during the lactation than ewes with birth
rank of a3 (Table 4), although this difference was only
significant at 60 days.
This is likely because 75% of the
ewes having multiple births were in the 2.5 BCSL group at
lambing.
The interaction of birth rank and BCSL was
significant due to the increase in BCS from 30 to 60 days
for the ewes giving birth to twins while the ewes having
multiple births decreased slightly during this time period
(Figure 3).
Breed of mating sire had no effect on BCS although ewes
bred to Columbia sires tended to have higher BCS's during
the first month of lactation (Table 4).
Sex of lambs influenced BCS (P=0.106); ewes nursing
twin females tended to have a higher BCS at each month of
lactation, particularly at the second month, whereas ewes
35
nursing mixed twins (male, female) tended to have a lower
BCS at each month of lactation (Table 4).
Daily Milk Yield
Using parturition date as a covariate, the final least
squares model included all the explanatory variables (BCSL,
sex of lambs, age of ewes, mating sire and birth rank), the
interactions of BCSL with birth rank and with sex of lambs,
the interactions of age of ewe with breed of sire and with
time (30, 60 and 90 days of lactation), and the interactions
of time and the explanatory variables.
Milk yield declined linearly (P<0.001) from 30 to 90
days of lactation; the slopes of the regression lines for
the two treatment groups (BCSL = 2.5 and 3.5) were similar
(Figure 5).
Average daily milk yield was similar between ewes of
BCSL = 2.5 and ewes of BCSL = 3.5 (Table 5).
Following
adjustment for explanatory variables, milk secretion was the
same for the two treatment groups at 30 days, the 2.5 BCSL
ewes were 8% higher (P=0.75) at 60 days, whereas milk
secretion was 33% higher (P=0.24) in the 3.5 BCSL ewes at
the third month.
The interaction of the independent
variables and time was not significant, nor were the
interactions significant among the independent variables.
Although not significant, ewes at 4 yr of age consistently
36
produced less milk each month than the older ewes (5 to 7
Although not significant, ewes nursing twin female
yr).
lambs secreted more milk than ewes nursing twin male lambs.
Analysis of the simple means indicated that ewes with
the higher BCSL tended to produce more milk each month
(Figure 6).
This difference was significant at the third
month.
Milk Composition (Fat & Protein)
Body condition score at lambing had no effect on
percent milkfat during the lactation (Table 6).
Percent
milkfat decreased significantly during lactation, but
primarily from the first to the second month (P=0.002 for
quadratic effect).
Age of ewe had no effect on percent
milkfat although the 4-year-old ewes generally had the
highest milkfat percentage each month.
Although not
significant, ewes having twin lambs at birth consistently
had higher percent milkfat over the entire lactation than
ewes having multiple lambs at birth.
Ewes mated to Columbia
rams had higher (P.0.047) percent milkfat at 30 days but not
at 60 days (P=0.164) or 90 days of lactation (P=0.999).
of lambs had no effect on percent milkfat.
Sex
The large
standard errors of the mean precluded detecting differences
between the various main effects.
37
Ewes with a higher BCSL (3.5) had slightly higher
percent milk protein at 30 and 90 days of lactation, whereas
the percent milk protein of ewes with a lower BCSL (2.5) was
significantly higher at 60 days of lactation, yielding a
significant interaction of time and treatment
(P=0.032)(Table 7).
Percent protein in milk increased
significantly in a quadratic fashion, primarily from 30 to
60 days of lactation (Figure 7).
Older ewes tended to have
higher percent milk protein during lactation, but this
difference was only significant at 90 days and over the
entire lactation when the 7-year-old ewes were higher than
the 4- and 5-year-old ewes.
Ewes giving birth to twin lambs
had higher percent milk protein each month of lactation, but
this difference was significant only at 90 days.
Ewes mated
to Polypay rams had slightly higher percent milk protein at
30 days of lactation and this difference increased with time
(P=0.056 at 60 days; P=0.005 at 90 days).
Ewes nursing twin
male lambs tended to have higher percent milk protein during
lactation; at 60 days of lactation ewes nursing twin males
were higher (P=0.020) than ewes nursing mixed-sex twins.
Lamb Weight
Total weight born (TWB), adjusted to twin lambs, was
analyzed for the main effects and the interactions of BCSL
with sex of lambs and with birth rank and the interaction of
38
age of ewe with breed of mating sire.
Birth weight of lambs
sired by Columbia rams were heavier (P=0.12) than lambs
sired by Polypay rams and birth weight of lambs born as
twins were heavier (P=0.006) than the adjusted birth weight
of twin lambs born as multiple births (3)(Table 8).
The
interaction of BCSL with birth rank approached significance
(P=0.09); total birth weight of twin lambs born from ewes
with a lower BCSL (2.5) were heavier than twin lambs from
ewes with a higher BCSL (3.5) whereas lambs from multiple
births were heavier than twin births from ewes with a higher
BCSL (3.5).
Using parturition date as a covariate, the final
statistical model for total lamb weights included all the
explanatory variables (BCSL, sex of lambs, age of ewes,
breed of mating sire and birth rank), the interaction of
breed of sire with birth rank, time (30, 60 and 90 days of
lactation), and the interactions of time and the explanatory
variables.
Lamb weights were similar at 30 and 60 days but the
lambs of ewes having BCSL = 2.5 gained weight more rapidly
thereafter and were heavier at 90 days of lactation
(P=0.155) and at weaning (P=0.096)(Table 9).
Lamb weight
increased over time, exhibiting a cubic effect (P=0.005).
Body weights of lambs nursing 4-year-old ewes tended to be
lower whereas body weights of lambs nursing 7-year-old ewes
tended to be higher at each month of lactation.
This
39
difference was significant at 30 days and 60 days of
lactation.
Lamb weights from multiple birth litters tended
to be heavier throughout lactation; this difference only was
significant (P=0.054) at 30 days of lactation.
Lambs sired
by Polypay rams were heavier (P=0.02) throughout lactation.
This difference increased during lactation, yielding a
significant interaction (P=0.01).
The interaction of time
and treatment was also significant (P=0.003); lambs of ewes
with BCSL = 3.5 gained weight more rapidly prior to 60 days
whereas lambs of ewes with BCSL = 2.5 gained weight more
rapidly from 60 days to weaning at 95 days (Figure 8).
The
interaction of age of the ewes with time (P=0.084) was due
to lambs of the 4-year-old ewes being heavier than lambs of
the 5- and 6-year-old ewes at 60 days but not during the
other times of lactation.
Twin female lambs were heavier
(P=0.02) at weaning than twin mixed-sex lambs.
The
interaction of sex of lambs with time (P=0.007) was caused
by heavier weights of the mixed-sex twin lambs than the twin
male lambs at 30 days postpartum whereas the twin male lambs
were heavier at 90 days of lactation and at weaning.
40
Table 2. Least square means of colostral immunoglobulin
(IgG) concentrations and total weaning
weight of lambs (0,1,2) at 95 days of age
as affected by body condition score at
lambing (BCSL), age of ewe, mating sire and
birth rank.
IgG
(mg/ml)
Category
Weaning
weight
No.
ewes
(kg)
n
x
2.5
37
60
4.1
38
43.5
2.49
3.0
31
56
4.2
35
47.2
2.48
3.5
25
58
5.7
28
41.4
2.88
4 yr
23
57
6.0
26
47.6be
3.06
5 yr
18
66
6.7
20
43.8b
3.24
6 yr
32
55
3.6
34
53.1'
2.56
7 yr
20
53
7.2
21
31.7a
3.50
Polypay
49
59
3.6
52
50.0a
2.03
Columbia
44
57
4.4
49
38.0b
2.17
2
58
61
2.8
z3
35
55
5.3
SE
n
x
SE
BCSL
Age of ewe
Breed of sire
Birth rank
'b'Means in column within a category with different superscripts
differ (P<0.05).
41
Table 3
Lamb mortality classified by body condition score
at lambing (BCSL), age of ewe, mating sire,
sex of lambs and birth rank.
Lamb mortality
Category
Born
Killed
Natural
death
n
n
n
Total
lambs
lost
n
Lamb
mortality
rate
No.
lambs
weaned
BCSL
2.5
76
7
9
16
21.1
60
3.0
66
4
4
8
12.1
58
3.5
51
2
8
10
19.6
41
193
13
21
34
17.6
159
4 yr
50
4
6
10
20.0
40
5 yr
36
1
5
6
16.7
30
6 yr
69
3
5
8
11.6
61
7 yr
38
5
5
10
26.3
28
100
6
9
15
15.0
85
93
7
12
19
20.4
74
88
6
9
15
17.0
73
105
7
12
19
18.1
86
1
8
1
0
1
12.5
7
2
109
7
8
15
13.8
94
3
51
3
7
10
19.6
41
4
19
1
4
5
26.3
14
5
6
1
2
3
50.0
3
Total
Age of
ewe
Ram breed
Polypay
Columbia
Sex of
lambs
male
female
Birth
rank
Table 4. Least square means of body condition score as affected by body condition score
at lambing (BCSL), age of ewe, birth rank, mating sire and sex of suckling
(twin) lambs.
Days post partum
Category
30
60
_
x
90
_
x
Overall
mean
n
x
2.5
26
2.46a
.056
26
2.56
.062
26
3.10
.067
2.71
.041
3.5
15
2.666
.082
15
2.68
.090
15
3.15
.097
2.83
.059
12
2.92a
.094
2.61'
.057
3.14'b
.132
2.89b
.080
3.27b
.074
2.796
.045
3.19'6
.131
2.806
.080
SE
n
SE
n
SE
SE
BCSL
Age of ewe
4 yr
2.50ab
.079
12
2.40a
.087
12
5 yr
5
2.75'
.110
5
2.776
.121
5
6 yr
19
2.49b
.062
19
2.60'b
.068
19
2.50'b
.109
5
2.70b
.120
5
25
2.60
.058
25
2.75a
.064
25
3.19
.070
2.85
.042
16
2.52
.073
16
2.50b
.080
16
3.07
.087
2.69
.053
25
2.50
.054
25
2.56
.060
25
3.08
.065
2.75
.039
16
2.62
.074
16
2.54
.082
16
3.04
.089
2.79
.054
Males
7
2.60
.086
7
2.62'd
.094
7
3.13
.102
2.79
Females
.062
7
2.59
.099
7
2.73'
.108
7
3.19
.118
2.84
.072
27
2.48
.060
27
2.50d
.065
27
3.06
.071
2.68
.043
7 yr
Birth rank
2
3
Ram breed
Polypay
Columbia
Sex of
5
lambs
Male\Female
Overall mean
2.56
2.62
.052
.057
3.13
''b Means in column within a category with different superscripts differ (P<0.05)
cd Means in column within a category with different superscripts differ (P=0.06)
.062
I.
NJ
Table 5. Least square means of milk yield (ml) as affected by body condition score at
lambing (BCSL), age of ewe, birth rank, mating sire and sex of suckling
(twin) lambs
Days postpartum
Category
__30
n
60
90
Overall
mean
x
SE
n
x
SE
2385
2209
304.4
25
1347
207.6
465.9
15
1794
317.8
2331
2421
2127
2352
2369
269.6
n
x
SE
SE
BCSL
2.5
25
3262
369.1
25
3.5
15
3259
565.0
15
12
2921
515.8
12
1911
425.4
12
1547
5
3610
745.4
5
2159
614.7
5
1287
18
3328
417.0
18
2050
343.9
18
1729
290.1
419.3
234.6
5
3182
639.5
5
3069
527.4
5
1721
359.8
2657
334.3
2
24
3185
397.6
24
2554
1751
223.6
3335
485.4
16
2041
16
1391
273.0
2497
2256
207.8
16
327.9
400.3
24
a3
3239
366.0
25
2110
301.9
25
1557
521.4
15
2485
430.0
15
1584
205.9
293.3
2302
3282
2450
191.3
272.5
2987
547.1
7
2195
451.2
7
1577
307.7
2253
285.9
3662
622.2
7
2014
513.2
7
1602
350.0
2426
325.2
3132
370.6
26
2683
305.7
26
1534
208.5
2450
193.7
3260
342_3
2297
282_3
1571
392 6
Age of ewe
4 yr
5 yr
6 yr
7 yr
Birth rank
Ram breed
Polypay
25
Columbia
15
Sex of lambs
Males
7
Females
7
Male\
26
Female
Overall mean
192.9
295.3
389.6
217.9
253.7
Table 6. Least square means of percent fat in milk as affected by body condition
score at lambing (BCSL), age of ewe, birth rank, mating sire and sex
of suckling (twin) lambs.
Days postpartum
Category
30
n
_
x
60
SE
n
_
x
90
SE
n
_
x
SE
Overall
mean
SE
BCSL
2.5
25
11.50
.617
25
9.24
.707
25
9.08
.676
3.5
9.94
.550
14
11.90
.652
14
9.54
.747
14
8.29
.714
9.91
.581
11
12.07
.641
11
9.94
.734
11
9.18
.702
10.39
5 yr
.571
5
12.03
1.075
5
9.44
1.231
5
7.82 1.178
6 yr
7 yr
9.76
.957
18
11.06
.524
18
9.34
.601
18
9.26
.574
9.89
.467
5
11.64
1.105
5
8.84
1.266
5
8.48 1.211
9.66
.984
23
12.06
.498
23
9.80
.570
23
9.21
.545
10.36
.443
16
11.34
.777
16
8.97
.889
16
8.16
.851
9.49
.692
23
10.99'
.487
23
8.83
.558
23
8.69
.533
9.50
.434
16
12.41b
.674
16
9.95
.772
16
8.69
.738
10.35
.600
7
12.04
.964
7
10.02
1.104
7
9.42 1.056
10.49
.859
7
12.12
.781
7
9.30
.895
7
8.98
10.14
.696
9.14
.505
Age of ewe
4 yr
Birth rank'
2
3
Ram breed
Polypay
Columbia
Sex of
lambs
Males
Females
.856
Male\Female
25
10.93
.568
25
8.84
.650
25
.622
7.65
Overall
11.71
.481
9.38
.550
8.67
.526
a'b Means in column within a category with different superscripts differ (P<0.05)
c
(P=0.016)
Table 7. Least square means of percent protein in milk as affected by body condition
score at lambing (BCSL), age of ewe, birth rank, mating sire and sex of
suckling (twin) lambs
Days postpartum
Category
30
60
n
x
SE
n
BCSL
2.5
25
4.00
.080
25
3.5
14
4.05
.102
14
11
3.92
.104
5
3.98
18
Age of ewe
4 yr
5 yr
6 yr
7 yr
Birth rank
2
3
x
90
SE
Overall
mean
SE
5.22
.097
4.71
.068
5.29
.124
4.66
.087
11
5.01'
.125
4.53a
.088
5
5.02'
.172
4.57.1°
.120
5.30°b
.104
4.74ab
.073
5
5.68b
.198
4.90b
.139
.092
23
5.41°
.109
4.78
.076
.095
16
5.10b
.113
4.59
.079
.100
4.83'
.070
.124
4.54b
.087
.160
4.81
.112
.169
4.64
.118
.097
4.61
.068
SE
n
x
4.918
.081
25
4.64b
.104
14
11
4.64
.105
.142
5
4.73
.144
4.09
.086
18
4.83
.087
18
5
4.11
.164
5
4.89
.166
23
4.08
.090
23
4.85
16
3.97
.093
16
4.70
Ram breed
Polypay
23
4.10
.083
23
4.90c
.084
23
5.49°
Columbia
16
3.95
.103
16
4.64d
.104
16
5.01b
Sex of lambs
Males
7
4.12
.133
7
5.00a
.135
7
5.32
Females
7
3.97
.140
7
4.71ab
.142
7
5.23
Male\ Female
25
3.99
.080
25
4.62b
.081
25
5.21
Overall mean
4,02
.068
4.78
.069
5.25
Means in column within a category with different superscripts differ (P<0.05)
Means in column within a category with different superscripts differ (P=0.056)
.082
46
Table 8. Least square means of total weight born
(twin lambs) as affected by body
condition score at lambing (BCSL), age
of ewe, birth rank, mating sire and sex
of suckling (twin) lambs.
Category
Total weight born, kg
n
x
SE
2.5
27
8.3
.35
3.5
16
9.2
.53
4 yr
12
8.1
.49
5 yr
6
8.8
.62
6 yr
20
8.7
.36
7 yr
5
9.3
.58
2
26
9.5.
a3
17
8.0b
.45
Polypay
25
8.3
.36
Columbia
18
9.2
.47
Males
8
8.7
.49
Females
7
9.0
.61
28
8.6
.33
BCSL
Age of ewe
Birth rank
.35
Ram breed
Sex of
lambs
Male\
Female
a.b Means in column within a category with different superscripts
differ (P<0.05)
Table 9. Least square means of total lamb weights' (kg) at 30, 60 and 90 days postpartum
and at weaning (95 days) as affected by body condition score at lambing (BCSL),
age of ewe, birth rank, mating sire and sex of suckling (twin) lambs.
n
x
Days postpartum
rn
qn
Category
SE
n
x
90
SE
n
x
SE
n
x
SE
BCSL
2.5
21
21.9
.83
21
36.1
1.25
21
55.2
1.52
21
60.3
1.92
3.5
13
22.4
.76
13
36.6
1.14
13
52.3
1.39
13
55.9
1.76
10
20.7b
.78
10
35.68b
1.17
10
52.0
1.44
10
55.5
1.81
5
21.2b
1.06
5
35.08b
1.60
5
54.7
1.95
5
58.6
2.47
17
20.9b
.60
17
34.5b
.91
17
52.4
1.11
17
58.8
1.41
2
25.88
1.61
2
40.28
2.42
2
55.8
2.96
2
59.6
3.75
21
21.1'
.68
21
35.6
1.02
21
53.3
1.25
21
58.6
1.58
13
23.2d
.86
13
37.0
1.30
13
54.1
1.58
13
57.6
2.01
20
22.9
.73
20
37.5
1.09
20
55.78
1.34
20
60.9'
1.69
14
55.46
1.70
4
59.7'1'
3.05
6
60.1°
2.25
24
54.56
1.58
Age of ewe
4 yr
5 yr
6 yr
7 yr
Birth rank
2
3
Ram breed
Polypay
Columbia
14
21.5
.73
14
35.2
1.10
14
51.76
1.34
Sex of lambs
Males
4
20.5
1.31
4
35.3
1.97
4
54.8
2.41
Females
6
23.4
.97
6
38.3
1.46
6
55.0
1.78
Male\
24
22.6
.68
24
35.3
1.02
24
51.3
1.25
Female
ab Means in column within a category with different superscripts differ (P<0.05)
Means in column within a category with different superscripts differ (P=0.054)
Only ewes that weaned twin lambs are included in the analysis.
'
Table 10. Correlation coefficients for ewe and lamb characteristics (Exp. 1).
TWBF
BCSL
-.25*
TWBF
TWBA
TWBA
-.05
.42"
WWT
HR
AGE
RANK
TRN
DL12
-.02
.01
.22*
-.25*
-.27"
.08
-.08
.26"
.08
-.09
.07
.44"
.13
.02
.32"
.09
-.17
.34"
-.16
.34"
-.21*
-.03
-.14
-.07
.00
.08
.64"
-.36"
-.33
-.02
.08
-.04
.16'
-.02
.07
-.07
-.16
.09
-.05
.02
.04
-.11
.29 **
.33"
.07
-.37"
.01
-.04
WWT
IgG
-.46"
HR
AGE
.75"
-.17a
RANK
TRN
DL12
P<0.01;
IgG
DED
-.07
P<0.05; a P<0.10
BCSL = Body condition score at lambing; TWBF = unadjusted total birth weight of lambs; TWBA
adjusted total birth weight of lambs; WWT = total weaning weight of lambs; IgG =
immunoglobulin concentration; HR = time from lambing to colostrum collection; AGE = age of
the ewes; RANK = birth rank; TRN = number of lambs turned out to pasture; DL12 = number of
lambs died before bumming; DED = number of lambs died after turned out to pasture.
49
Table 11. Correlation coefficients of some ewe and lamb characteristics during lactation (Exp. 2).
BCSL
BCSI
BCS2
LMB
WTI
LMB
WT2
LMB
WWT
.19
35*
.36*
.24
.16
-.28*
.31*
.20
.06
-.01
-.29'
-.29*
-.11
31*
34*
.40*
.29a
.04
.36*
-.10
-.12
.25
.42 **
A5**
39*
.26
.13
.10
.08
-.06
.06
.20
31'
.31"
.29"
-.29'
-.26'
.21
-.23
.21
.26
31*
.26
28*
.28'
.22
-.11
-.08
.13
-.14
-.09
.21
.30'
34*
.21
.21
.07
.43**
.21
33*
.25
-.23
-.10
.19
32*
32"
.22
-.10
-.15
.12
.12
.12
.03
.21
-.05
-29'
-.03
-.12
-.12
.01
.20
.00
.01
.55**
.08
.464.4,
_Spit.
....23
-.18
35*
.37*
32
.28
.16
.55**
A3**
.18
.18
-.17
-.10
-.27*
-.13
.20
-.13
-.15
-.14
-.03
.724*
.14
.16
.10
-.04
-.27"
-.08
35*
.02
-.10
-.12
-.08
.08
.14
.19
.00
-.23
-.11
.26'
-.09
-.18
-.16
-.03
.49**
.47**
.40**
-.38*
.03
.33*
.48**
.56**
39*
.27
.30"
-.02
.02
-.13
-.04
.07
A5**
.32'
.25
.22
-.09
-.02
.17
.19
.10
-.07
-.20
-.19
-.01
.43**
.48**
.30`
.27
32'
-.24
-.63-
-.38*
-.26
-.32'
-.25
.14
.11
-.05
-.07
-.06
.71"
.57"
.63"
.84"
.88"
37*
BCS1
BCS2
BCS3
MKY1
MKY2
MKY3
PRTI
PRT2
PRT3
FATI
FAT2
FAT3
SCC1
SCC2
scC3
AGE
RANK
SIX
TWB
.44**
.42**
.40**
.24
.09
.41**
.28"
-.21
.20
-.03
.03
-.02
.14
-.04
.19
.25"
-.23
-.21
.62**
37*
-.03
.03
.42**
.24
-.22
.02
.12
.22
.11
.10
.08
.19
.02
-.21
.61**
.10
.06
.38*
.43**
-.28*
.19
.11
.19
-.00
-52**
.20
.22
.294
.20
.03
36*
.42**
-.06
.35*
.04
.06
-.02
.51**
.22
.25
.15
-.04
.21
-.12
-.06
.01
.22
.17
.03
.18
.22
-.26'
-.41**
-.17
-.02
.11
-.14
-.10
.02
-.27'
-.20
.22
.05
.14
.14
.48**
-.15
.13
.48**
.09
-.11
BCS3
MKY I
MKY2
MKY3
PRT1
PRT2
PRT3
FATI
FAT2
FAT3
SCC1
SCC2
SCC3
AGE
RANK
SEX
TWB
LMBWT1
LMBWT2
LMBWT3
.91**
wT3
.61**
.72**
.84**
** P<0.01; * P<0.05; a P<0.10
BCSL = Body condition scores at lambing; BCS1 =-first month; BCS2 = second month; BCS3 = third month of lactation; MKY1 = average daily milk yield at first month; MKY2 =-second month; MKY3 = third month of lactation; PRT1 = percentages of
protein in milk at first month; PRT2 = second month; PRT3 = third month of lactation (PRT3); FAT' = percentages of fat in milk at first month; FAT2 = second month oflactation; FAT3 = third month; SCC1 = somatic cell count at first month; SCC2 =
second month; SCC3 = third month of lactation; AGE = age of ewes; RANK = birth rank; SEX = sex of the nursed (twin) lambs; TWB = total birth weight of the nursed (twin) lambs; LMBVsT1 = total (twin) lamb weight at first month; LMBWT2 = second
month; Ll'ABWT3 = and third month of lactation; WWT = total weight of the weaned lambs (twin).
50
Figure 2. Linear regression of ewe colostrum immunoglobulin
(IgG) concentrations on time of collection after
parturition (Exp. 1).
Figure 3. Least square means of body condition score during
lactation of ewes of different body condition scores
at lambing (BCSL) and of different birth rank at
lambing (Exp. 2).
51
Figure 2
120
,
E
cm
E
CD
cm
1-4
100
80
60
40
20
2
8
6
Time Postpartum (Hr)
4
12
10
Figure 3
3.5
o 2.5 BCSL
3.5 BCSL
Birth rank=2
a)
L_
0
(.)
v)
c
0
Birth rank3
3.0
43
0c
00
>,
-0
2.5
0
cc)
2.0
30
60
Days Postpartum
90
52
Figure 4. Least square means of body condition score during
lactation of ewes of different ages at parturition
(Exp. 2).
Figure 5. Linear regression of least square means of daily
milk yield of ewes of different body condition score
at lambing (BCSL) (Exp. 2).
53
Figure 4
3.5
O 4 years of age
A 5 years of age
O
* 6 years of age
o 7 years of age
0
U)
3.0
2.5
2.0
30
60
Days Postpartum
90
Figure 5
+
...--.
L
6000
x
Y = 4181
3.5 BCSL
27.4X
R2 = 0.3273
-0
0
2.5 BCSL
Y = 3726
27.7X
R2 = 0.3239
4000
_.v
--±'
>-.
° 2000
a__
oo
30
60
Days Postpartum
90
54
Figure 6. Linear regression of actual daily milk yield of ewes
of different body condition score at lambing
(BCSL) (Exp. 2).
Figure 7. Least square means of percent fat and protein in
milk during lactation of ewes of different body
condition score at lambing (BCSL)(Exp. 2).
55
Figure
2.5 BCSL
E
Y = 3726
27.7X
R2 = 0.3239
6000
x
3.5 BCSL
Y = 4181 - 27.4X
R2 = 0.3273
-o
a)
>- 4000
_y
>,
(Is 2000
0
30
Figure
12
10
I
60
Days Postpartum
90
O 2.5 BCSL
35 BCSL
Milk Fat
a)
0
a)
CL
Milk Protein
30
_a
60
Days Postpartum
90
56
Figure 8. Least square means of total lamb weight during
lactation of ewes of different body condition score
at lambing (BCSL)(Exp. 2).
57
Figure 8, continued.
60
50
40
30
20
10
30
60
Days Postpartum
90 W
58
CHAPTER 5
DISCUSSION
Colostrum Experiment
Colostrum
The concentration of immunoglobulins in colostrum
decreases rapidly with time.
Correlation coefficient
analysis indicated that colostral IgG concentration was
negatively correlated to time of sample collection (r=
0.46; P<0.01; Table 10).
Linear regression analysis of the
data, collected from 0 to 11 hr postpartum, projected a
level of 76 mg/ml at parturition (Figure 2), and with a
slope of -3.28, colostrum IgG levels would decrease to 0 at
about 23 hr postpartum.
Shubber et al.
(1979) collected
colostrum over a 48 hr period and observed that
concentrations of total immunoglobulins (IgG, IgM, IgA) had
decreased to low levels by 36 hr postpartum.
A study of
dairy cattle (Stott et al., 1981) over the first 6 milkings
(12 hr intervals) postpartum also indicated a linear decline
(semilog plot) in milk IgG concentration with time (slope
-0.293).
Although the unadjusted concentration of colostral IgG
(57 ± 2.3 mg/ml) is not directly comparable since samples
were collected up to 11 hr postpartum, they compare
59
favorably with Thomas et al.
(1988) and Gilbert et al.
(1988) who collected colostrum at parturition and reported
concentrations of IgG similar to mine (64 ± 7.6 and 80 ± 2.4
mg/ml, respectively).
Hunter et al.
(1977) also collected
colostrum at parturition but observed IgG concentrations 2-
fold higher (115 ± 10.1 mg/ml) than mine and, similar to my
8-fold range between individual ewes (14-114 mg/ml),
observed a 6-fold range (43-260 mg/ml) between ewes.
Shubber et al.
(1979) reported mean levels of total
immunoglobulins ranging from 71 ± 11 to 203 ± 28 mg/ml in
colostrum collected from 1 to 12 hr after parturition.
Different reagents for the radial immunodiffusion assay and
the variability between ewes probably account for the major
differences between studies.
I did not observe differences in colostral IgG
concentrations due to BCSL, age of ewe, breed of mating sire
or birth rank (Table 2).
Similarly, Thomas et al.
(1988),
in a study involving 3-yr-old Finn-Targhee ewes, failed to
detect differences in colostral IgG concentrations of ewes
having BCSL of 2.5 or 3.5 (64 ± 7.6 vs 67 ± 7.5 mg/ml).
Although Thomas et al.
(1988)
(twins vs triplets) and
Halliday (1974)(singles vs twins) did not observe an effect
of birth rank, Gilbert et al.
(1988) reported a linear
increase in colostral IgG concentrations as birth rank
increased (singles, twins and triplets).
I observed an
60
opposite trend in our study; colostral IgG concentrations
were lower (P =0.06) in ewes having multiple lambs (3) than
in ewes having twins.
However, our analysis did not include
singles and all multiple litters were pooled.
In a large
study (N =1686) involving several breeds and ages of ewes,
Gilbert et al.
(1988) found that yearling ewes had
concentrations of colostral IgG (100 ± 7.3 mg/ml)
significantly higher than older ewes (2-7 yr) but found no
difference due to age among the older ewes.
Gilbert et al.
(1988) also observed higher concentrations of colostral IgG
in Polypay ewes (80 ± 2.4 mg/ml) than in Columbia ewes (64 ±
2.1 mg/ml); I did not observe any difference (P>0.10)
between Polypay ewes mated to Polypay rams (59 ± 3.6 mg/ml)
and Polypay ewes mated to Colombia rams (57 ± 4.4 mg/ml).
Lamb Mortality
Lamb mortality was not affected by BCSL, age of ewe,
breed of mating sire, sex of lamb, or birth rank (Table 3).
The majority (81%) of the natural death loss (10.9%)
occurred at birth (stillborn) or within 2-3 hr after birth.
Predator kill was 6.7% which, when added to the natural
death loss, yielded a total death loss of 17.6% from birth
to weaning.
Gilbert et al.
(1988) reported a death loss of
12.3% and found that 52% of the deaths resulted from
61
infectious diseases.
They observed differences due to breed
(higher in Targhee, lower in Polypay and Finn) and found
that death loss was 3-4x greater in lambs having serum IgG
levels slO mg/ml.
from 7.71%.
1992).
Others have reported death losses ranging
(Young and Dickerson, 1987) to 15.796 (Otesile,
Previous studies at Oregon State University (Khan,
1994; Nawaz and Meyer, 1992; Nawaz et al., 1992), observed
differences in lamb survival due to the effect of breed in
some, but not all, trials.
They also reported a positive
relationship between body condition of the ewe and lamb
survival.
Our narrow range of BCS's (2.5 to 3.5) may have
precluded us from observing this effect.
Kleemann et al.
(1993), however, reported that lamb survival was not
influenced by the nutritional status of the ewe during mid
and late pregnancy.
A negative relationship (r= -0.21; P<0.05) was observed
between early death loss (DL12) and adjusted total birth
weight (TWBA), indicating that neonatal death loss was lower
in lambs having a heavier birthweight (Table 10).
Similar
findings by others (Alexander, 1964; Mellor, 1990; Jordan
and Feuvre, 1989) have been attributed to the failure of
smaller birthweight lambs to compete successfully for milk.
The positive correlation (r=0.13; P>0.10) between neonatal
death loss (DL12) and unadjusted total birth weight (TWBF)
was expected since the smaller birthweight lambs were in the
62
larger birth ranks.
This is reflected in the large positive
correlation (r=0.33; P<0.01) between early death loss (DL12)
and birth rank (RANK).
The negative correlation (r= -0.33;
P<0.01) between death loss in pasture (DED)(largely predator
kill) and total weaning weight (WWT) can be attributed to
the higher weaning weight of surviving lambs.
The negative correlation (r= -0.25; P<0.05) between
BCSL and unadjusted total birth weight (TWBF) can be
attributed to the negative relationship between BCSL and
birth rank (RANK)(r. -0.25; P<0.05); ewes with higher BCSL
had a lower birth rank, yielding a lower TWBF (Table 10).
The correlations between the number of lambs turned out to
pasture at 2-3 weeks postpartum (TRN) and birth weight
(TWBF, TWBA) and weaning weight (WWT) were positive and of
the opposite sign of early death loss (DL12) as expected,
since TRN and DL12 are opposites.
Heavier birth weight
lambs have a lower death loss.
Lactation Experiment
Body Condition Score
Body condition score of ewes with a higher BCSL (3.5)
decreased significantly (240) from lambing to first milking
(30 days postpartum) whereas the BCS of ewes with a lower
63
BCSL (2.5) only decreased by 1.6% during this interval
(Table 4).
Peart (1970) observed even a greater loss in
condition score (390) in ewes with a high BCSL (3.1) whereas
ewes with a low BCSL (1.1) did not decline in BCS.
Similarly, Gibb and Treacher (1980, 1982) observed that ewes
with a higher BCSL (3.2) lost condition more rapidly early
in lactation (first 10 weeks) than ewes with a lower BCSL
(2.8), but that by 16 weeks postpartum, the condition loss
was the same between the two groups.
Since we failed to
detect differences in milk yield at 30 days of lactation
between the 2 treatment groups (Table 5), the greater loss
of BCS in ewes with the higher BCSL (3.5) was likely due to
decreased DMI, since Cowan et al.
(1980) has shown that DMI
decreases as body fatness increases.
After the initial decrease in BCS from parturition to
30 days, the BCS increased in both treatment groups from 30
to 90 days postpartum (Figure 3), although ewes with the
lower BCSL (2.5) gained body condition more rapidly during
lactation and were only 1.6% lower than the high BCSL group
by 90 days of lactation.
Although not significant, we found that ewes with a
higher birth rank had a lower BCSL (r= -0.23; Table 11),
indicating that ewes with a higher birth rank had a larger
demand for nutrients by the fetuses during pregnancy,
resulting in a lower BCSL.
This is similar to the
64
significant correlation (r= -0.25; P<0.01) we observed in
Experiment 1 (Table 10) between these two factors.
Similarly, Khan (1994) observed a significant decrease in
birth rank in ewes having a higher BCSL in 1 of 7 trials he
conducted.
The positive correlations between BCSL and the BCS's at
30, 60 and 90 days and between the BCS's at those times
(Table 11) indicates that the scoring was repeatable when
performed each time by the same individual.
Milk Yield
The lactation period in sheep varies in length,
depending on the environment and management.
Lambs may be
weaned as early as 40 days or as late as 130 days
postpartum.
In this study, since adequate forage was
available, we chose to wean the lambs at 95 days postpartum.
Milk production normally peaks at 3-4 weeks postpartum
and then exhibits a linear decline during the remainder of
the lactation (Peart, 1967).
example, observed
Reynolds and Brown (1991), for
peak daily milk yield (2,459 ml/day) at
2-4 weeks of lactation and then a decline to 1,142 ml/day at
106 days of lactation.
(Since many of the studies report
milk yield in units of grams, we have converted these data
to milliliters using a factor of 1 ml = 1.035 g (Torres-
65
Hernandez and Hohenboken, 1979).
Ramsey et al.
(1994)
reported peak milk yield at 14 days of lactation.
In their
study, ewes nursing twins produced more milk (3,108 and
4,176 ml/day) than ewes nursing singles (2,136 and 2,664
ml/day) on days 4 and 14, but not on days 50 (2,352 vs 2,112
ml/day), 89 (1,260 vs 1,584 ml/day) or 106 (1,056 vs 1,056
ml/day, respectively) of lactation.
The objective of this study was not to determine peak
milk production but to begin the milking study after the
peak of production (day 30) so that we could study the rate
of decline in milk yield during the lactation.
Daily milk
yield at 30 days of lactation (3,260 ± 342 ml)(Table 5) was
higher than that reported by Reynolds and Brown (1991) at 30
days (2,376 ± 130 ml), Shabbir et al.
(1992) at 30 days
(2,204 ml), Torres-Hernandez and Hohenboken (1979) at 21
days (1,795 ml), Brown and Hogue (1985) at 28 days (1,414
ml) and Langlands (1973) at 31 days (1,728 ml).
Others,
however, have reported milk yields slightly higher (Snowder
and Glimp, 1991
3,434 ml at 28 days; Ramsey et al., 1994
3,336 at 14 days) than ours.
Our estimate of total milk yield (231 1) for the 95-day
lactation (2.43 l/d) is higher than the estimates of 189 1
in 89 d (2.12 l/d) by Gardner and Hogue (1964), 142 1 in 70
d (2.03 1/d) by Snowder and Glimp (1991), 129 1 in 70 days
(1.84 l/d) by Peart (1970), and 137 1 in 70 d (1.96 l/d) by
66
Peart (1967).
Our estimate is based on a linear regression
equation (Y = 4035 -30.1607X) calculated from the overall
least square means (Table 5).
An examination of the milk yield data (measured over a
comparable time period) from other experiments revealed that
they observed a similar rate of decline (negative regression
slope) in milk yield (Langlands, 1973, b= -18.9; Snowder and
Glimp, 1991, b= -36.7; Reynolds and Brown, 1991, b= -16.6;
Torres-Hernandez and Hohenboken, 1979, b= -15.1) as we found
(b= -30.2).
Simultaneous with the decline in milk yield,
Langlands (1973) reported a linear increase in grass
consumption with age of the lambs.
Geenty (1985) observed
that milk production is a good predictor of lamb growth up
to 4 weeks of age, after which grass consumption becomes an
important variable.
We did not observe differences in milk yield due to
BCSL, age of ewe, birth rank, breed of mating sire or sex of
lambs (Table 5).
The adjusted milk yields were the same the
first month but the ewes having the higher BCSL (3.5)
produced 33% more milk (P=0.24) at 90 days of lactation.
An
analysis of the simple means indicated that the ewes having
the higher BCSL produced more milk each month, although the
difference was only significant (P<0.05) at 90 days of
lactation (Figure 6).
Gibb and Treacher (1980), in
agreement with our data, also observed a slight advantage in
67
milk yield in ewes having a higher BCSL (3.2 vs 2.4), and
this difference was only significant later in lactation
(weeks 9-12).
Others have failed to observe a difference in
milk yield between ewes of different BCSL (Jordan and Hanke,
1991; Peart, 1968; Gibb and Treacher, 1982).
Peart (1967)
reported that ewes, severely undernourished during
pregnancy, produced less milk the first week of lactation,
but produced similar amounts of milk at the peak of
lactation and for the entire lactation as ewes that were
well nourished during pregnancy.
In a later study, Peart
(1970) found that milk yield was influenced by BCSL but only
when the forage supply was restricted.
Since our ewes were adjusted to twin lambs shortly
after parturition, we failed to note the increased milk
yield in ewes nursing twins compared to ewes nursing singles
as reported by Gardner and Hogue (1964), Ramsey et al.
(1994), Slen et al.
(1963), Snowder and Glimp (1991),
Torres-Hernandez and Hohenboken (1979), and Gibb and
Treacher (1982).
Torres-Hernandez and Hohenboken (1979) observed that
age of ewe (3- vs 4-yr-old) had no effect on milk yield and,
in a later study (Torres-Hernandez and Hohenboken, 1980),
they found that sex of lamb was not a factor.
Birth rank
was not a factor influencing milk yield in a study by Knight
and Bencini (1993).
Snowder and Glimp (1991) compared the
68
Rambouillet, Columbia, Polypay, and Suffolk breeds and
concluded that milk yield was not affected by breed of ewe.
Torres-Hernandez and Hohenboken (1979) reported a
negative correlation (r= -0.25; P>0.10) between BCS at the
end of lactation and total milk production.
Our
correlations were positive between milk yield and BCS at 90
days of lactation (r=0.36; P<0.05) and between BCSL and milk
yield at 30 (r=0.24; P>0.10), 60 (r=0.09; P>0.10), and 90
days (r=0.41; P<0.01) of lactation (Table 11).
The
significant correlation at 90 days of lactation is in
agreement with our analysis of simple means for milk yield
in which ewes with the higher BCSL (3.5) produced more milk
each month but the difference was only significant at 90
days of lactation (Figure 6).
We failed to detect significant correlations between
milk yield and lamb growth.
The correlations ranged from
r=0.20 at day 30 to r=0.26 at day 60 and r=0.21 at day 90
(P>0.10) of lactation (Table 11).
Others have noted
significant correlations between these two factors but
primarily early in lactation (Geenty, 1980; Geenty et al.,
1985; Reynolds and Brown, 1991; Snowder and Glimp, 1991) and
primarily in ewes nursing single lambs (Torres-Hernandez and
Hohenboken, 1980; Ramsey et al., 1994).
Brown et al.
(1987)
observed that milk yield was only a good predictor of lamb
growth until the third or fourth week of lactation.
Gardner
69
and Hogue (1964), however, reported a correlation
coefficient of 0.83 between total milk yield and 90-day lamb
weights.
A decline in these correlations during lactation
was not observed in my experiment because milk yield and
lamb weights were not measured until 30 days of lactation,
when the lambs had already begun supplementing their diets
with forage.
Ramsey et al.
(1994) stated that milk yield is
a more limiting factor for twins whereas singles have ad lib
access to milk which can express itself more directly in
growth of lambs.
Langlands (1973) reported that lambs
increase forage intake to compensate for reduced milk
supply, thus maintaining an equivalent growth rate.
Milk Composition
Milkfat percentage decreased from 11.71 ± 0.481% at 30
days to 8.67 ± 0.526% at 90 days of lactation (Table 6),
averaging 9.92% during the entire lactation.
These levels
are considerably higher than 6.48% reported by Brown and
Hogue (1985), 6.99% reported by Brown et al.
(1987), and
6.65% reported by Torres-Hernandez and Hohenboken (1979).
Our milkfat percentages would change only slightly
(Corrected fat% = -1.09 + 1.11(IRMA %fat)) if corrected for
infrared analysis as suggested by Reynolds and Brown (1991).
Percent milkfat was not significantly correlated with milk
70
yield; some correlations were positive and some negative
(Table 11).
In contrast to the decrease in percent milkfat
that we found, Torres-Hernandez and Hohenboken (1979)
observed an increase in percent milkfat during the
lactation, but they only reported values at 8
(7.13%) weeks of lactation.
Shabbir et al.
(6.17%) and 12
(1992), in a
study involving various levels of dietary calcium, reported
milkfat percentages (11.6%) as high as ours in some of their
dietary groups, and a decrease in milkfat percentage in some
dietary groups from the first to the second month of
lactation.
Milk protein, however, increased during lactation from
4.02 ± 0.068% at 30 days to 5.25 ± 0.082% at 90 days (Table
7).
1985
Others have reported similar levels (Brown and Hogue,
4.49%; Brown et al., 1987
Brown, 1991
4.81%; Reynolds and
4.51%; Torres-Hernandez and Hohenboken, 1979
4.90 %) during lactation.
Our results agree with Torres-
Hernandez and Hohenboken (1979) who reported an increase in
percent milk protein during the lactation.
Snowder and
Glimp (1991) found that milk protein percentage was high
immediately after parturition, decreased to a low at 8
weeks, and then increased again at 12 and 14 weeks of
lactation.
In our study, ewes mated to Polypay rams had a
higher milk protein percentage (4.83 ± 0.070%) than ewes
mated to Columbia rams (4.54 ± 0.087%); Snowder and Glimp
71
(1991) did not detect differences due to breed of the ewe's
sire.
Torres-Hernandez and Hohenboken (1979) observed a
significant effect of the breed of the ewe's sire on
percentage milk protein but not on the percentage milkfat.
Also in our study, milk protein percentage was higher in 7yr-old ewes than in 4-yr-old ewes at 90 days and over the
entire lactation; Torres-Hernandez and Hohenboken (1979)
found no difference in milk composition between 3- and 4-yrold ewes.
There was a slight positive relationship between
percentage milkfat and milk yield each month, whereas
percentage milk protein was negatively correlated with milk
yield at 60 (r= -0.41, P<0.01) and 90 days (r= -0.20,
P>0.10) of lactation (Table 11).
Somatic cell count (SCC) may be an indication of an
inflammatory response in the udder, but it is not a direct
indicator of mastitis.
In dairy cattle, there is a negative
regression of SCC on milk yield.
We observed a negative
correlation (r= -0.29; P<0.10) between milk yield and SCC at
60 days, but not at 30 or 90 days of lactation (Table 11).
The positive correlations between the SCC at 30 days with
the SCC at 60 days (r=0.49, P<0.01) and 90 days (r=0.47,
P<0.01) of lactation indicates that ewes with a high SCC at
30 days tended to have high SCC's at 60 and 90 days of
lactation.
Older ewes had higher SCC at 30 days (r=0.40;
P<0.01) and 90 days (r=0.22; P>0.10) but not at 60 days (r=
72
-0.02; P>0.10) of lactation.
Torres-Hernandez and
Hohenboken (1979) observed decreased milk yield (11.5%) in
ewes with mastitis in half of the udder and a larger
decrease (58.3%) in milk yield in ewes with mastitis in both
halves of the udder.
They reported an overall mastitis
incidence of 11.5% in their study.
Lamb Weights
There was no effect of BCSL on birth weight of lambs
born (adjusted to twins), although birth weights were
slightly heavier (P =0.15) for ewes with a higher BCSL (Table
8).
Similarly, Gibb and Treacher (1980, 1982) found no
difference in lamb birth weights in their studies, which
compared ewes of high (3.2-3.3) and low (2.4-2.6) BCSL.
Peart (1968) and Khan (1994) found the same relationships
whereas Russel et al.
(1977) observed that birth weights
declined when ewes were undernourished during gestation.
Kleemann et al.
(1993), however, found that birth weights
were unaltered by the level of nutrition during mid and late
pregnancy.
Thomas et al.
(1988) reported that lamb birth
weight was greater (P<0.10) for ewes with a higher BCSL
(3.5) than for ewes with a lower BCSL (2.5).
But ewes in
that experiment had similar birth ranks in both treatment
groups whereas, in our study, ewes with a lower BCSL had a
73
higher birth rank (r= -0.23; P>0.10; Table 11).
This
relationship was significant in the first experiment (r=
0.25; Table 10).
Older ewes had fewer (r= -0.19; P>0.10) but heavier
lambs at birth (r=0.43; P<0.01; Table 11).
High birth ranks
consisted of lambs with lower birth weights (r= -0.63;
P<0.01), similar to the results reported by Kleemann et al.
(1993).
Nawaz and Meyer (1992a) observed a curvilinear
effect of ewe age on lamb birth weight; birth weights were
the lowest in yearling ewes.
In my experiment, lambs sired by Columbia rams tended
to be heavier (P>0.10) at birth than those from ewes mated
to Polypay rams (Table 8), but, during lactation and at
weaning, lambs sired by Polypay rams were heavier.
This
difference was significant at 90 days and at weaning.
Nawaz
and Meyer (1992) observed that lambs were smaller at birth
from Polypay- and Coopworth-sired ewes than lambs from
Suffolk-sired ewes.
Ewes with multiple births (3) had
lighter lambs at birth than ewes with twins (Table 8).
Since all litters were adjusted at birth to twins, litters
of twins born as twins would be heavier than twins selected
from multiple-birth litters.
Neither growth of lambs nor weaning weights were
affected by BCSL (Table 9).
This is in agreement with Gibb
and Treacher (1982) who reported that the nutritional status
74
of ewes during pregnancy had no affect on the growth rate of
lambs.
Khan (1994), however, who had a wider range of BCSL
(2.5-4.0), reported that ewes with a higher BCSL weaned
heavier lambs.
Our lack of differences due to BCSL is not
surprising, given that milk yield did not differ between
treatment goups.
Although only significant at 30 and 60 days of
lactation, lambs of 7-yr-old ewes were heavier at birth
(Table 8) and at each period of lactation and at weaning
(Table 9).
Nawaz and Meyer (1992) reported that yearling
ewes weaned the lightest lambs and that weaning weight
increased with parity.
Similar to birth weights, they also
found that weaning weights from Polypay-sired ewes were
intermediate between Suffolk- and Coopworth-sired ewes.
We
observed that twin female lambs were heavier than twin male
lambs at 30, 60, and 90 days of lactation, whereas twin
males were heavier at birth (Table 8) and at weaning.
After
60 days, twin males gained weight faster than twin female
lambs.
It is interesting to note that, although lambs from
twin-bearing litters were heavier at birth than lambs of
multiple litters (Table 8), lambs of multiple litters were
heavier at 30 days (P=0.054) and slightly heavier at 60 and
90 days of lactation (Table 9).
75
Conclusion
Under these conditions (multiparous ewes and spring
lambing)
I conclude that, in the colostrum experiment, a
BCSL ranging from 2.5 and 3.5 had no affect on colostral IgG
concentration, mortality rate or weaning weights of lambs.
In the lactation experiment, BCS of the ewes after the first
month of lactation was similar for ewes with 2.5 and 3.5
BCSL. The BCS of ewes that had a BCSL of 3.5 decreased by
24% during the first month of lactation while the BCS of
ewes with a BCSL of 2.5 only decreased 1.6% during the same
time.
Milk yield and milkfat percent were not affected by
the difference in BCSL but milk protein percent was higher
at the second month of lactation in ewes with 2.5 BCSL.
Milk protein percent, however, was similar between the two
groups at the first and third months of lactation.
Ewes
mated to Polypay rams secreted a higher percent milk protein
than ewes mated to Columbia rams.
Body condition score at
lambing had no affect on the total weight of lambs born or
the growth rate of lambs during the lactation period.
76
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