Frequency of calving in PGF2a estrous synchronized cattle
by Robert Jay Kautz
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in
Animal Science
Montana State University
© Copyright by Robert Jay Kautz (1985)
Abstract:
Three consecutive years of calving records were analyzed to evaluate the frequency of calving for
synchronized versus control cattle. Reproductive performance including mean day of calving , length
of the calving season and statistical differences between number of calves born during selected days of
the calving season were analyzed , for PGF2α. synchronized (n = 511 ) and non-synchronized control
(n=401) cows. Controls were artificially inseminated (AI) 8-12 hours after first observation of standing
estrus. Synchronized cattle received PGF2α (25 mg. free acid) either in the p.m. of day 4 ( 1 9 75 ) or
the a.m. of day 5 ( 1976 and 1977 ) of breeding unless they had been observed in standing estrus prior
to these times. Inseminations to detected estrus continued in treated cattle until 80 + 4 hours post
PGF2α treatment. After this time all remaining animals were inseminated and recorded as non-estrus
bred. Breeding seasons consisted of 25 days AI plus 20 days natural service ( 1 975 and 1 976 ) or 8.5
days AI plus 48.5 days natural service (1977). During the 1975 breeding season a group of
two-year-old first calf cows were also tested. During the 1977 breeding season the cattle were divided
into two synchronized groups and one control group. Treatment 1 (T1 = AILAIE) consisted of AI at
standing estrus up to day 5 of the breeding season, then on the a.m. of day 5 an injection of PGF2
followed by AI at standing estrus up to 80+4 hours post estrus detection. Treatment 2 (T2=LAIE)
consisted of an injection of PGF2α during the a.m. of day 5 of the breeding season followed by AI at
standing estrus up to 80+4 hours post estrous detection. Results for 1976 showed that the mean day of
calving was significantly different (p < . 05 ) for both groups of cows tested. The mean day of calving
for mature cows was 24.5 days for synchronized versus 28.3 days for controls. For synchronized
two-year-olds the mean day of calving was 21.5 days versus 27.9 days for controls. The mean day of
calving was not significantly different (p>.05) for the 1977 calving season. During 1978 the mean days
of the calving season were T1=22.2, T2 = 20.7, and C = 25.3 days respectively. A significant difference
(p<.05 ) occurred for Tg versus C only. Significant differences (p< . 05 ) occurred during days 11-20
and 21-50 for mature cows and during days 1-10 and 11-20 for two-year-old cows during the 1976
calving season. During 1977 significant differences were recorded during days 11-20 and 21-40 for AI
sired calves. A signiicant difference (p<.05 ) was recorded in 1 978 during days 1-5 for T2 versus T1
and C. FREQUENCY OF CALVING IN PGF2o<.ESTROUS
SYNCHRONIZED CATTLE
by
Robert Jay Kautz
A thesis submitted in partial fulfillment
of the requirements for the degree
of
Master of Science
in
Animal Science
MONTANA STATE UNIVERSITY
Bozeman, Montana
. April 1985
APPROVAL
of a thesis submitted by
Robert Jay Kautz
This paper has been read by each member of the thesis
committee and has been found to be satisfactory regarding
content, English usage, format, citations, bibliographic
style, and consistency, and is ready for submission to the
College of Graduate Studies.
Date
Chairperifan, Gr^srauate /Committee
Approved for the'Major Department
Head, Major Department
Approved for the College of Graduate Studies
Date
Graduate Dean
iii
STATEMENT OF PERMISSION'TO USE
In presenting this thesis in partial fulfillment of the
j
requirements
for
a m a s t e r ’s d e g r e e
at
Montana
State
University, I agree that the Library shall make it available
to borrowers
from
this
under
thesis
rules
are
of the Library.
allowable
without
Brief quotations
special
permission,
|
,E
’
u
provided that accurate acknowledgement of source is made.
Permission for extensive quotation from or reproduction
of this
his
i.j
thesis may be granted by my major professor, or in
j
absence, by the Dean of Libraries when, in the opinion
I
of either, the proposed use of the material is for scholarly
-I
purposes.
:I
for
Any copying or use of the material in this thesis
financial
permission.
S ignature
Date
gain
shall
not
be allowed without my written
:I
I|
]
I would like to dedicate this thesis to the memory of
my father, Kenneth L . Kautz, and Dr. E . L . Moody.
My father
was involved in agriculture his entire life and had a great
deal of influence on my college career. Dr. Moody was the
major influence on my attending graduate school and had a
special understanding of students and the problems they
encounter in college.
This thesis is written as much for
them as it is for me.
V
VITA
R o b e r t Jay K a u t z was born J a n u a r y 10, 1956, in
Estherville, Iowa.
He received elementary and secondary
education in Hamilton, Montana, graduating in May 1974.
He enrolled at Colorado State University in September
1974.
In the fall of 1975 he enrolled at Montana State
University and received a bachelor of science in animal
science in June 1979 . In September of 1979 he started work
towards a master of science degree in the Animal and Range
Science Department at Montana State University.
vi
ACKNOWLEDGEMENTS
I would
like
to thank
ray graduate
committee, P . J .
Burfening, R . P . Ansotegui, and L . L . Jackson.
have
instructed
courses
providing
and tests,
both
thanks
to
Thanks
not
a
several
insight,
learning
Kent
Higgins,
cribbage
undergraduate
thought
and
and
stimulating
enjoyable
Gail
good
and
Vennes
I would
Betty
and
like
George
Thanksgiving and Christmas
express
Stewart
assignments
experience.
and
conversation
to
graduate
They made graduate
Henry
in
the
to Rolinda Coffey for typing this thesis.
least
parents
in
and not all too often humor.
school
casino,
me
These people
sincere
for
Special
Connor
grad
putting
room.
Last,
thanks
me
for
but
to my
up
at
and for not asking too often why
it took so long to finish this thesis.
vii
TABLE OF CONTENTS
Page
LIST OF TABLES......................... .... ..........
LIST OF FIGURES...........
viii
ix
ABSTRACT......
x
1.
I
2.
3.
4.
INTRODUCTION....................... '.............
ESTROUS SYNCHRONISATION.........................
3
Progesterone Injections...................
Oral Progesterone Compounds....................
Subcutaneous Implants...........................
Prostaglandins.........
3
5
8
10
MATERIALS AND METHODS...........
15
RESULTS AND DISCUSSION...........................
19
1976 Results................
I977 Results.....................................
1978 Results.....................................
Conclusions......................................
25
28
36
LITERATURE CITED......................................
39
19
viii
LIST OF TABLES
Page
1.
2.
3.
Influence of Day of Calving Season on Number
of Cows Calving, 19 76....-....................
21
Influence of Day of Calving Season on Number
of Cows Calving, 19 77 .........................
29
Influence of Day of Calving Season on Number
of Cows Calving, 1978.........................
■ 33
LIST OF FIGURES
Page
1.
1976 Cows Percent Calving Five-Day Intervals...
23
2.
1976 Two-Year-Olds Percent Calving FiveDay Intervals . ..................................
24
3.
19 76 Cows Al Sired Five-Day Intervals..... .
26
4„
1976 Two-Year-Olds Al Sired Five-Day Intervals.
27
5.
1977 Cows Percent Calving Five-Day Intervals...
30
6.
19 77 Cows Al Sired Five-Day Intervals....-......
31
7.
19 78 Cows Percent Calving Five-Day Intervals. . .
34
8.
19 76 Cows Al Sired Five-Day Intervals..........
35
X
ABSTRACT
Three
c o n s e c u t i v e . years of calving records were
analyzed
to e v a l u a t e the f r e q u e n c y of c a l v i n g for
synchronized
versus
control
cat tl e.
Reproductive
performance including mean day of calving , length of the
calving season and statistical differences between number of
calves born during selected days of the calving season were
a n a l y z e d , for PGFgc^ s y n c h r o n i z e d
(n = 5 I I ) and nonsynchronized
control
( n = 4 0 I ) cows .
C o n t r o l s were
artificially inseminated
(Al)
8-12 ■ hours after first
observation of standing estrus.
Synchronized cattle
received
mg. free acid) either in the p.m. of day
4 (1975 ) or the a.m. of day 5 (1976 and 1977 ) of breeding
unless they had been observed in standing estrus prior to
these times.
Inseminations to detected estrus continued in
treated cattle until 80+4 hours post PGFg^treatment.
After
this time all remaining animals were inseminated and
recorded as non-estrus bred.
Breeding seasons consisted of
25 days Al plus 20 days natural service (1975 and 1976) or
8.5 days Al plus 48.5 days natural service (1977).
During
the 1975 breeding season a group of two-year-old first calf
cows were also tested.
During the 1977 breeding season the
cattle were divided into two synchronized groups and one
control group. Treatment I (T1 = AlLAIE) consisted of Al at
standing estrus up to day 5 of the breeding season, then on
the a.m. of day 5 an injection of PGF2 followed by Al at
standing estrus up to 80+4 hours post estrus detection.
T r e a t m e n t 2 (T2 =LAIE) c o n s i s t e d of an i n j e c t i o n of
PG F2 ^ during the a.m. of day 5 of the breeding season
followed by Al at standing estrus up to 80+4 hours post
estrous detection. Results for' 1976 showed that the mean day
of calving was significantly different (p < .0 5 ) for both
groups of cows tested.
The mean day of calving for mature
cows was 24.5 days for synchronized versus 28.3 days for
controls.
For synchronized two-year-olds the mean day of
calving was 21.5 days versus 27.9 days for controls.
The
mean day of calving was not significantly different (p>.05)
for the 1977 calving season.
During 1978 the mean days of
the calving season were T 1=22.2, T2 =20.7, and C =25.3 days
respectively.
A significant difference (p< .05 ) occurred for
T2 versus C only.
Significant differences (p<.05 ) occurred
during days 11-20 and 21-50 for mature cows and during days
1-10 and 11-20 for two-year-old cows during the 1976 calving
season.
During 1977 significant differences were recorded
during days 11-20 and 21-40 for Al sired calves.
A
signiicant difference (p < .05 ) was recorded in 1978 during
days 1-5 for T2 versus T 1 and C .
I
CHAPTER I
■ INTRODUCTION
Beef
and dairy producers
employing prostoglandin, Fg
estrous
double
injection
injection
during
12 days
1-4
is
and
systems
apart)
the
conjunction
studied
One
that
it
17-21
fails
of
(involving
that
included
disadvantage
to
two
artificial
single
of the
manipulate
the estrous
cycle.
injections
H o w e v e r , a double
number
of
times
increase costs during breeding.
sh o w n
have
with
for
and
single
cattle
Double
of PGFgoc IQ to
have been developed to allow manipulation of
groups.
increase
in
systems.
system
days
injection
these
Systems
are now
(PGFg =>< ) and its analogues
synchronization
insemination.
in the United States
a
single
injection
animals
are
system
will
handled
and
Several recent studies have
injection
of
25
mg.
P G F g c^
intramuscularly produces more calves per unit of semen,
and
is lower in total cost and cost per pregnancy than a double
injection
system
(Vennes
1981;
artificial
insemination pregnancy
Whitman,
1981).
Total
rates are comparable for
single and double injection systems
(Vennes,
1981).
However
data concerning the frequency of calving during the calving
seasons
compare
is
obscure.
The
synchronized
to
objectives
of this
control
calving
study were
seasons
to
and
2
statistical
selected
differences
days
of
the
in
numbers
calving
of
calves
season,
synchronized versus non-synchronized cows.
born
for
during
PGFg=*
3
CHAPTER 2
ESTROUS SYNCHRONIZATION
Progesterone Injections
Christian
and
Casida
(1948)
showed
that
14
daily
injections of progesterone in corn oil suppressed estrus and
prevented
(1950)
ovulation
conducted
during
a similar
the
treatment
period.
Willett
study to determine the fertility
of yearling heifers artificially inseminated at first estrus
following progesterone injections.
Beginning on the 14th or
15th
continuing
day
days,
were
of
daily
bred
later.
the
The
observed
average
were
in
and
estrus
from
and
for
13 to
the last
effective
in
study
observed, that
inhibiting
estrus
before estrus occurred.
g r o w t h , injections
cycle.
Smaller
however,
follicles
treatment
ceased.
must
doses
be
started
prevented
developed
Dosages
and
24
hours
treatment
a range of 4 to 7 days.
17
Animals
again
11 pregnancies were obtained.
a similar
administered
standing
interval
5 days with
total breeding
(1951)
cycle
injections of 50 to 100 mg. were used.
at
estrus was
estrous
to
Out of 22
Ulberg et al.
dosages
and
of 50 mg.
ovulation
if
To inhibit follicular
before
estrus
ovulation
day
and
15 of the
ovulation;
occurred
when
less than 12.5 mg. were reported
to have little if any effect.
Hansel and Trimberger
(1952)
4
showed
that
small
a d m i n-i s t e r e d
dosages
at
the
of progesterone
beginning
of
the
(5 to
10 mg.)
estrous
cyc le
significantly reduced the length of estrus and the time from
end of estrus
to ovulation.
that
injection
a single
progesterone
estrus
the
of
and
in
ovulation
estrous
the
starch
cycle
heifers
controlled
injection
1120 mg.
was
(1956)
of
capable
administered
at
occurred
heifers
examined
low
shown
to
have
conception
of
(17
preventing
time
during
In 95 percent
following
at
single
rate
showed
crystalline
any
ovulation
All
were
a
and Cole
treatment was given.
examined,
but
to
emulsion
when
estrus
ovulations,
of 540
when
estrus.
Nellor
the
or
the
post
multiple
percent)
was
obtained with this method of treatment.
Ulberg
and
of 12.5 mg.
Lindley
(I960)
of progesterone
found
that
inhibited
daily
injections
estrus and ovulation,
but had a depressing effect upon pregnancy rates in animals
inseminated
injection
days
during
of
after
0.5
the
estrus
to
last
following
1.0 mg.
treatment.
estradiol
injection
A
benzoate
(EB)
of progesterone
single
three
initiated
estrus and ovulation without a further detrimental effect on
pregnancy rate.
estrous
cycle
Twenty-six
period.
Of
the
service.
of
Hansel et a l . (1961) attempted to alter the
using
27
Fourteen
26
progesterone
heifers
came
of
26
animals
these
bred
50
and
into
oxytocin
estrus
expressed
percent
injections.
in
estrus
conceived
an
8 day
in 3 days.
at
first
Pregnancy was checked by rectal palpation 60 days
5
after
Al,
and
calving
dates
confirmed
earlier
pregnancy
diagnoses.
Wiltbank
progesterone
and
et a I . (1965 ) conducted
and
acetophenone
progesterone
estradiol
to
was
estradiol
either
enanthate
lower
than
showed that
reduced
controls
of
alone
(ENT).
100 percent, however,
trials
combination, and
derivative
(AD)
three
a
a progesterone
16«-* - I?=*. d i h y d r o x y -
or
in
combination
Synchronization
fertility
using
in the
in all trials.
varied
with
from 70
treatment
groups
Woody et al.
(1967)
ten daily injections of 100 mg. of progesterone
estrus
cycle
length
from
20.7
days
in
controls
to
16.7 days in treated cows.
Oral Progesterone Compounds
Oral progestatinal
to
try
to
injections
circumvent
for estruos
compounds were studied
the
labor
of
synchronization.
daily
in the 1960s
progesterone
The four compounds
most studied were:
1.
6
-methyl-1 7«-*-acetoxy progesterone
(MAP).
2.
6-chloro- A ^- 17 acetoxy progesterone
(CAP).
3.
6 ^ -methyl
6-dehydro-1 I-methyIene-17-acetoxy-
progesterone (MGA).
4.
16«_*-17 = dihydroxy
progesterone
acetophenonid.e
(DHPA)
Nellor
the
normal
et a l . (I 960 ) observed
ration
at
levels
that MAP
ranging
fed as part of
from 0.2 to 0.8 mg.
MAP/pound body weight daily by twice a day feeding for 15 to
6
20
days
inhibited
regardless
started.
0.2 mg.
However,
all
levels
of
treatment
level,
ovulation without estrus occurred at the
and at levels of 0.4 mg. or greater complete
of
follicular
treatment period.
the
at
of the stage of the estrous cycle when treatment
inhibition
of
estrus
growth
occurred
during
the
Estrus occurred 4 to 5 days after the end
treatment
period
with
the
0.4 mg.
dosage.
As
the
dosages increased, the duration from the end of treatment to
start of estrus increased.
Nelms
and Combs
(1961),
Similar results were reported by
Zimbelman
(1961 ) and Fahning et al .
(1966) all using MAP.
Graves
trophin
and
(HCG)
Dzuik
(1968)
used
human
after treatment with MAP.
chorionic
gonado­
A 60 hour interval
from withdrawl of MAP to the HCG injection with an interval
from HCG to insemination showed the best results.
al.
(1974) observed
Graves et
good results feeding MAP in conjunction
with an intramuscular injection of estradiol IT^5, .
seven
of 29
cows
exhibited
Twenty-
estrus between 24 and 216 hours
after MAP withdrawl.
Van
to
Blake
0.025
effective
estrus
animals
post
et al.
( 1962 ) fed CAP at varying
m g ./pound/head/day.
in
inhibiting
in a range
in the
treatment
estrus.
All
Treated
of 4 to I3 days
lower
levels
period.
No
levels
showing
animal
levels 0.3
proved
animals
to
be
exhibited
after w i t h d r a w l , with
estrus
earlier
in
conceived
when
bred
synchronized estrus in the 0.3 m g . group.
the
at
7
Studies
al.
(1963)
done
by Van Blake et al . (1963 ) and Wagner
showed
similar
results
as
those
stated
et
above.
Wagner et al. (1968) observed that CAP treated heifers had a
lower fertilization rate and a lower 60-day pregnancy rate.
Hansel et al . (1966 ) reported that in cows fed -MAP and
CAP
satisfactory
fertility
at
cattle than
estrous
the
synchronization
syncronized
estrus
in those fed CAP.
was
was
obtained, but
higher
in MAP
fed
Fertility was uniformly high
at the estrus subsequent to synchronization.
Wiltbank
estrus
and
Kasson
by feeding DHPA
estradiol
valerate
(1968)
successfully
in conjunction
(E V ) .
Results
synchronized
with an injection of
showed that approximately
the same percentages of treated animals were in estrus in a
3-day
period
21-day
the
as
compared
period.
The
synchronized
to control
conception
estrus
was
rate
lower
animals
after
than
in estrus
one
in a
breeding
at
that of the control
animals.
Zimbelman
and
Smith
(1966)
route of administration of M G A .
MGA daily inhibited
studied
dosage
effect
and
Oral doses of 0.25 to 8 mg.
estrus and ovulation.
Intravenous
(IV)
injections of 0.4 mg. daily were shown, to inhibit ovulation.
Lower
doses
by either
IV or oral
administration were shown
to inhibit estrus but not ovulation.
MGA was reported to be
approximately 300 to 900 times as potent as MAP, but only 10
to 15 times as potent when compared by IV.
8
Young
minimal
et al.
(1967)
effective
dose
reported
for
that 0.4 mg. MGA was the
suppression
of estrus.
Roussel
and Beatty (1969) reported a 93 percent occurrence of estrus
after
feeding
MGA
days,
and
overall
an
at
1.0 mg./head/day
conception
for
rate
14
consecutive
(first
and
second
service) of 60 percent as compared to 53 percent for control
animals.
Subcutaneous Implants
Subcutaneous
pessaries
implants,
and
using progestational
with injections
intravaginal
compounds,
sponges
and
or in conjunction
of estradiol were studied in order to learn
the feasibility of this type of estrus synchronization.
Dzuik
implants
et
al.
(1966)
impregnated
percent
of
the
70
observed
with MGA
cows
that
silicone
synchronized
tested.
rubber
estrus
A subcutaneous
in 64
implant
containing 17-ethyl 19 nortestosterone (Nilevar) was studied
by Wiltbank et al . (1971) to determine its effectiveness at
estrous
synchronization
estrus.
Of the
87 percent
fertility
at
15 heifers that were
showed
estrus
16 days
after implant removal
implanted
for 9 days and received‘an injection of EV on the
implantation.
The
the
for
to
of
of
synchronized
implanted
in 96 hours
percent
the
compared
day
93
and
42
percent
heifers
of
heifers
which
were
pregnant
at
synchronized estrus was greater in the group implanted for 9
days.
same
Pregnancy
as
in
the
9-day
that of the controls.
group
was
approximately
An injection
of
2 mg.
the
of
9
estradiol
which
17^ into
had
injection
percent
been
heifers
present
24
for
hours
after
9 days
and
implant
had
removal ,
received
an
of EV on the day of implantation caused 98 to 100
of
cycling
heifers
to
show
estrus
in
a 48-hour
period and 100 percent to ovulate in 36 hours.
Whitman
et
al . (I 9 72 ) reported
that
estrus
effectively synchronized using an ear implant
an
injection
level
of
6.5 mg.
of 7.5 mg.
fertility.
EV
EV
without
improved
Similar
results
lowering
shown
by
be
(SC21009)
and
fertility.
A
synchronization
were
could
but
decreased
Burrell
et
al .
(1972).
Woody
and
Pierce
of
treatment
initiation
using
norethandrolone
implanted
prior
to
(1974 ) studied
on
estrous
implants
10 days
and
the
effect
cycle
of day
Synchronization
EV injections.
postestrus
of
had
Heifers
longer
return
intervals than those implanted after 10 days postestrus.
Intravaginal
sponges
containing
studied by Garrick and Shelton
found
to
be
retained
longer
(1967).
than
progesterone
were
Bunched sponges were
cylindrical
sponges .
Sponges containing 100 mg. progesterone inhibited estrus and
ovulation
in the majority of the animals.-
Within five days
of cessation of treatment estrus occurred in 55.6 percent of
the animals.
Fertility after treatment with the sponges was
reported as unsatisfactory .and was not superior to fertility
reported
after
progesterones .
intramuscular
Sreenan
and
treatment
Mulvehill
or
feeding
of
( 1 975 ) reported
10
differences in percentages of retention of pessaries between
20
and
10
days
respectively.
(86.7
percent)
(93*6
percent )
Lower calving rates were observed in heifers
inseminated
in
estrus' following
those
at
in t e r v a I with
bred
and
the
the
20-day
10 — day
period, while
treatment
were
slightly higher than those of control heifers.
Prostaglandins
Prostaglandins
first
detected
They
are
in
(PGs)
are
seminal
now known
so
plasma
to be present
named
from
because
the
they
prostate
were
gland.
in most mammalian tissues
in very small amounts.
Th e i r
bas ic
structure
is
that
of
a
20
c a rbo n
monocarboxylic acid containing an internal cyclopentane ring
(Bohinski, 1979).
B* c» D> E>
F ) which
differences
synthesis
There are six different series of PGs (A,
in
the
occurs
from
are
differentiated
pentane
fatty
ring
by
structural
(Lehninger,
1977)
PG
acids with PGF2 ck being derived
from linoleic acid.
Since
Babcock
luteolytic
involving
factor
PG.
stated
that
PG
may
Trials
run in the
early 70s
showed
al.
the
occurred
( 1973 ) showed
that
by
the ips!lateral horn to the C.L. luteal
(Louis
et
a I.,
1972)
progesterone levels dropped (Liehr et al., 1972).
et
be
in the bovine many studies have been done
infusing PGF2o^into
regression
(1966)
that
IM
injections
and
blood
Stellflug
of PGF2ck.decreased
11
blood progesterone.
fertility
of
Lauderdale
cattle
et al. (1973 ) reported that
inseminated
at estrus
was comparable
to control animals.
reported
subcutaneous
cycle
that
caused 'animals
treatment.
using
Heersche
to
et al
estrus
(1974)
synchromate B implants
PGF2o4.
Hearnshaw et al. (1974)
injections
show
following
of
72
PGF2o4^during
to
reported
seven
days
80
hours
similar
prior
mid
after
results
to injection
of PGF2^ .
Graves
et
effectively
al.
( 19 7 5 ) reported
synchronized
that
with Norgestomet
estrus
can
be
implants followed
by administration of PGF 2c< the day prior to implant removal.
Administration
of
GNRH
reduced
the
mean
interval
from
implant removal to ovulation, reduced the variability in the
interval
from
implant
to
o v u l a t i o n , and
suppressed
occurrence of estrus.
Innskeep
in
cows
(EB)
et
al.
synchronized
(1975)
with
showed
PGF12 ^
higher
and
than when treated with PGF2o^only.
higher
percentage
after
treatment.
conception
estradiol
rates
benzoate
He also reported a
of EB cows showing estrus 48 to 84 hours
Welch
et
al.
(1976)
reported
similar
results using EB with PGF2cyt.
Lambert
et
al.
(1975)
reported
that
the
percent
of
cattle conceiving during the first ten days of the Al season
in a PGF2o^treatment group was greater than in a non-treated
control
group.
conception
would
This
move
trial
toward
showed
the
that
the average
beginning
of the
day
of
breeding
I2
season.
Higgins
(19 81 ) demonstrated that the same pregnancy
rates were achieved
for cattle
in. a 10 day PGF2 ^
as in a 21 day conventional system.
system
The calves produced by
synchronized cows were older and heavier than those produced
by
control
cows.
significantly
Cumulative
different
preganancy
(p <.0 5)
at
day
rates
10
were
but .total
pregnancy rates were not.
A
major
utilizing
the
PGF2o^is
estrous
injection
to
disadvantage
cycle
systems
12 days
apart
with
that
cows
fail
to
single
within
days
respond
involving
have
a
the
been
1-4
and
administration
system
17-21
to treatment.
developed
of these groups of animals.
injection
of
Double
of PGF2
10
to allow manipulation
Although all trials involved in
this sudy are single injection breeding systems it should be
noted that a double injection system may have affected some
of the results of this study.
cause
more
earlier
will
in the
shorten
number
of
injection
the
cows
breeding
the
times
season
available
season.
breeding
cows
system.
calving
single
to be
must
of cows
to be bred
season
but
handled
More
calves
may
when
compared
of the two PGF2c^treatments.
and
will
increase
compared
be born
system
the
to a single
earlier
during
to a conventional Al or a
s y ste m,
cycling
and conceive
A double injection
be
P G F 2^ treatment
percentage
A double injection system may
if
these
there
wer e
cows responded
a high
to one
13
Moody and Lauderdale
(1977)
compared
fertility of non-
treated control and two PGF2ca-treated (2x-25 mg. Tham salt)
groups.
Controls
were
bred
at observed
estrus
and treated
cattle were bred once at 80 hours following second treatment
or
by
estrous
detection.
First
service
conception
rates
were significantly lower (p<.001)
in appointment bred anmals
than
animals
in
controls ,
or
treated
bred
at
estrus.
Burfening et al . (1978) compared conception rates of treated
and
non-treated
control
cows
bred at observed estrus.
to
an
observed
Cattle
failing
estrus
to
were reinjected
(cows)
and
heifers.
first
following
exhibit
initial
estrus
within
co,ws
and
treated
heifers
cattle
controls.
next
11
that
appointment
were
by
estrus
(1978)
following
due
to
were
after
lower
bred
first
suggested
second
treatment
relatively
days
and 84
Analysis indicated
rates
bred
synchronization
comparable
the
conception
Johnson
treatment) was
PGF2oc treatment.
and appointment bred at 60 (heifers)
service
were
Treated heifers' and cows were bred
hours post post PGF2^in jection.
that
Controls
more
(p < .01 ) for
than
injection
the
and
enhanced
(versus
animals
both
initial
being
at
a
stage of the estrous cycle at the time of second
treatment.
Han
was
(1981)
improved
1 5 . mg.
dose
approximately
demonstrated
with
when
80
a dose
all
hours
of
that
25 mg.
cattle
after
estrous
the
synchronization
PGF2c:X_ compared
were
second
inseminated
injection
to
a
at
without
estrus detection.
system
to
Vennes
a double
injection
produced
per
unit
than
the
double
rates
in
were
reported
systems
not
of
semen
in
injection
significantly
similar
were
(1981) compared a single injection
results
lower
in
system.
the
single
system.
cost
that
and
pregnancy than double injection systems.
calves were
injection
Total
different.
showing
total
More Al
Al
pregnancy
Whitman
single
lower
in
system
(1981)
injection
cost
per
15
CHAPTER 3
MATERIALS AND METHODS
Records
from, estrous
synchronization
trials
conducted
by the Animal and Range Sciences Department of Montana State
University
in conjunction
Ranch
used
were
from
the
estrous
aged
for
spring
this
calving
synchronization
2 to
11
years
with
study.
The
herd
trials
that
the Montana
for
State
calving
1 976
-
records
1 978 .
involved mature
were
over
4 5 days
Prison
were
Yearly
suckled cows
post
partum.
Records from 1976 - 1978 also included virgin heifers age 12
to
20
months.
treatment
Mature
based
on
cows
previous
were
randomly
calving
dates
assigned
while
to a
yearling
heifers were assigned based on birth date (age).
Predominant breeds used in the trials were Hereford and
Hereford/Angus
crosses.
These
typical Montana range conditions.
hay
was
fed
on
an
as
needed
cattle
were
managed
under
During the winter alfalfa
basis.
All
animals
were
together on native range during the breeding season.
Cattle
were assigned to. either a treatment or a control group.
controls
were
artificially
after observed
PGF 2^ 25 mg.
( 1975 ) or
in
standing
free
the
acid
inseminated
estrus.
IM
morning
either
of
day
(Al)
8 to
run
All
12 hours
Treatment animals received
in
the
evening
of
day
4
5 ( 1976-1 977 ) of breeding
16
unless
they
times.
had
been
Breeding
cattle
until
remaining
to
80^4
bred.
days natural
service.
Two
Treatment
I
showed
morning
until
80
the
morning
estrus
estrus
post
animals
were
prior
continued
P G F 2 TX
of
8.5
days
treatment
standing
Al
groups
and
all
cows
all
of 25 days Al plus
20
plus
were
During
48.5
1977 the
days
tested
natural
in
1977.
inseminated
injected
not
iri treated
as
of day 5, Al then continued
when
these
recorded
artificially
estrus, then
to
w h i c h ' time
at
bred
consisted
(T^ ; AlLAIE) was
hours
inseminated.
in
service during 1975 and 1976 .
consisted
the
hours
Breeding
breeding
cows
detected
undetected
nonestrus
observed
with
PGF2 CX
if
in
at standing estrus
showing
estrus
were
Treatment 2 (T2 ; LAIE) cows were given PGF2^in
of
day
5 and
then
artificially
inseminated
at
standing estrus.
Initial
Al
with
individual
each
year.
services
Al
During
bulls
utilized
randomly
1975 and
Hereford
or Angus
assigned
to
1976 cattle observed
semen,
treatments
in estrus
within 15 days of initial Al service were reinseminated with
Red Angus
semen.
This was used as a genetic marker to aid
in determining which Al service resulted in conception.
For
1977 breeding season all repeat inseminations were with Red
Angus semen in conjunction with observation and recording of
natural
service
breeding
dates
for
an additional
for a total of 21 days estrus detection.
12.5
days
17
Day
of
olds)
was
cows
or
conception
based
280
Calculated
on
for
all
cattle
(cows
and
two-year-
actual calving dates minus 285 days for
days
for
conception
two-year-olds
dates
falling
gestation
within
+10
length.
days
of Al
breeding dates were considered as Al conceptions.
Length
birth
dates
season.
of
the
calving
of the first
The
first
calf
season
was
determined
by the
and the last calf born during the
born
was
assigned
season with following days numbered
day
I of the
consecutively until the
last calf was born.
In the spring of 1976 the season started April
continued until May 30th for a length of 60 days.
calving
19 th
for
season
started
a length
of
April
5th
4 5 days.
and
The
continued
1st and
The 1977
until
1 9 7 8 calving
May
season
started April IOth and continued until May 31st for a length
of 52 days.
All cows were checked daily and calving dates
were recorded as first visual sighting of calf.
The median (50'percent of total calf crop born) calving
date was
calculated
for each calving season for treated and
control groups.
Chi
square
differences
selected
tests
(p< .05)
days
were
used
to
analyze
significant
in the frequencies of calving tested at
of the
calving
season.
Histograms were used
treated
versus
to illustrate:
I.
The
percentage
of
calving at 5-day intervals.
control
cows
18
The
percentage
intervals.
of
Al
sired
calves
born
at 5-day
19
CHAPTER 4
RESULTS AND DISCUSSION
The
spring
cow
herds
divided -into' treatment
there
old
for
versus
was
also
a treated
first
calf
cows.
1 9 7 6 , 1977
control
versus
and
groups.
1978
were
During
1976
control group of two-year-
Two treatments
were used
during
1978
AILAIE (T1), and LAIE (T2 ).
1976 Results
Two hundred and twenty calves were born to mature cows,
118 to treated cows and 102 to control cows.
the
calving
season
in the treated
55 days for the control group.
mean
day
of
for treated
calving
group was 60 days versus
PGF2o<treatment affected the
(p < .05 ) , which
was 24.5
and control groups respectively.
Al sired calves (61 percent)
to 63 Al sired calves
One
The length of
hundred
and
and
28.3
days
There were 72
in the treatment group compared
(62 percent) for the control group.
sixty-seven
calves
were
born
to two-
year-olds in 1976, 82 calves from treated cows and 85 calves
from
control
cows.
Since
there
were
no
differences
in
either the way ^the treatment was administered or the lengths
of the
Al
season
for
treatment
or control
groups we can
assume that due to synchronization the length of the calving
20
season
in
the
days
for the
mean
day
treated
treatment
control
of calving
and
control
group
group.
which
cows
was
52
days
Treatment
was
21.5
compared
affected
(p< .05)
versus 27.9
respectively.
to
There
the
days
were
68
for
56
Al
sired calves (68 percent) born in the synchronized group and
52 Al sired calves (62 percent) born in the control group.
Chi
square tests were used to determine if significant
differences
in the
calving season.
frequency
of calving
for
both
percentage
calvig
groups
of mature
cows
Cumulative
had
compared
to 34 percent
calves were
considered
group
had
control
group.
year-olds
when
calved
occur
only
synchronized
did
Al
by
day
51
20
during
calves
( p <. 0 5)
for
Fifty-five
percent
of
day 20 of the
for
mature
cows
of all treated
for controls.
to
54
cows
When only
for
all
percent
of the
(p<.05 ) for
cows
considered.
earlier
tested
Again
twoand
more
in the calving season than
effects
both
A higher
83 percent of the treated
1-10
were
the
by
differences
days
Cumulative
difference
percent
compared
Significant
cows calved
controls.
20,
effects
that
sired
by day
cows tested.
calved
illustrate
Al
the
11-20 and 21-50 of the calving
of synchronized
sea so n.
calved
during
Table I illustrates significant differences
(p < .05 ) occurred during days
season
existed
illustrate
groups
treated
during
a significant
days
11-20.
two-year-olds
calved
compared to 36 percent of the controls.
When Al calves were
Table I
Influence of Day of Calving Season on Number of Cows Calving,
All 1976 Cows
1976 (%)
Al Sired
Days of
Calving
Season
n
days
I I-2 0
days
Treated
II8
13
(11)
47
(40)3
54
Control
101
8
(8)
26
( 2 6 )b
63
Treated
■ I 18
13
(ID
60
(51 ) a
Control
101
8
8)
34
( 34 ) b
21-50
I 1-20
days
21-40
days
( 46 ) a
72
14
(19)
46
( 64 ) a
12
(
I7 ) a
( 63 ) b
63
8
(1.3)
26
(41 ) b
28
(
44)b
I 14
(97)
72
14
(19)
'CO
0-10
n
O
kO
0-10
72
(100)
9.7
(96)
63
8
(13)
34
62
(
days
days
Cumulative
Effects
All
Days
Two- Year-Old
Cows
Al
m
CO
(
(54 ) b
98)
Sired
of
Calving
Season
n
n
0-10
I 1-20
days
days
21-50
days
n
n
0-10
days
11-20
days
21-35
days
Treated
82
22
( 2 7 )a
23
(28)
34
(41)
56
22
(39 ) a
23
(41)
11
( 20 )
Control
84
10
(12)b
20
(24)
46
(55)
52
10
(
I9 ) b
20
(38)
19
( 35)
Treated
82
22
(27 ) a
45
( 55 ) a
79
(96)
56
22
( 3 9 ) a
45
(80)3
56
(100)
Control
84
10
( 12 ) b
30
( 36 ) b
76
(90)
52
10
(
CO
51
(100)
Cumulative
Effects
bearing
different
super sc riots
are
m
columns
O
within
on
* Means numbers
different.(p<.05)
19)b
significantly
22
considered, 80 percent
of
the
treated
group
had
calved
by
day 20 compared to 58 percent of the control group.
The
calving
percentage
at
5 day
Twenty-six
11-15,
percent
versus
difference
to
intervals
of
the
a peak
in
days
did
season.
for
the
The
four
peaks
is approximately
the
calving
for
calved
distinct
for
after
difference
7 percent.
Figure
during
I.
days
This
(p = . 0 5 6 ) .
This
treatment
group
(13 percent) occurs
group.
The
peak during
the
(all)
group.
the
peak
cows
in
control
treatment
birthrate
greatest
cows
A second
one
The
illustrated
for
the
have
steady
is
control
significance
not
relatively
season.
40-45
versus
treated
percent
synchronization.
during
group
treatment
approaches
illustrates
due
16
of
control
day
control
the calving
group
show
a
15 of the calving
in peaks
for the controls
The peaks that occur
for both
groups at day 45 may be due to the repeat breeding that was
used
as
service
a genetic
resulted
marker
to
aid
in conception.
in determining which Al
The peak for the treatment
group would be smaller due to synchronization
because more
cows became pregnant early in the breeding season thus fewer
of the treated cattle were available to come into estrus and
be bred for subsequent calving at this time.
Figure
year-olds.
day
2
illustrates
relationship
for
two-
Again the treatment groups first major peak is a
15, however,
control
a similar
group
the second peak runs from days 35-40.
shows
two
definite
peaks
at days
25
The
and 45.
23
F i g u r e I. 1 9 7 6
Cows
Percent
_______________T r e a t e d = S o l i d L i n e ,
O
Calving
Five
Day
Intervals.
Control = Das h l i n e .
—
LU
DAY OF C A L V I N G SEASON
24
Figure 2. 1 976
Two-Year-Olds
P e r c e n t C a l v i n g Five Day
___________ Intervals.__Treated=Solid Line, Control=Dash Line
DAY OF C A L V I N G SEASON
25
Again
this
second
peak
may
be
due
to repeat
breeding with
the genetic marker.
Figure 2 also illustrates a difference
of
5 of
9 percent
correspond
at
day
to Table
the
I which
calving
shows
season.
this
a significant
would
difference
(p<.05) by day 10 of the calving season.
Figures
versus
olds
3 and 4 illustrate the relationship of treated
control cows, and treated
percent
illustrate
Al
sired
that
due
to
were
born
every
5 days
than
controls.
Peaks
treatment
groups.
at 5 day
versus control two-yearintervals.
synchronization
of the
occur
From Table
calving
during
Both
more
treated
season
days
cows
up to day
11-15
I and Figures
figures
for
15
both
1-4 we can see
that synchronization caused more calves to be born by day 20
of the calving season.
Synchronization caused a significant
difference
cumulative
(p< .05)
in
results
for
both
mature
cows and two-year-olds by day 20 of the calving season.
1977 Results
Two
the
hundred
1 977
control
and
calving
s e a s o n , I 4 3 to
treated
cows
born
during
and
13 0 to
in treated
cows was 43 days versus 45 days for control cows.
Treatment
23.7
not
affect
days
for
The
calves were
length of the calving season
did
cows.
seventy-three
the
mean
treated
day
cows
of
calving
versus
(p< .05 ) which
24.2
days
for
was
the
controls. There were 100 Al sired calves (70 percent) in the
treatment
group
versus
98 Al
sired
calves
(75
percent) in
26
Figure
3•
1976
Cows
Al
Sired
Five
_______________T r e a t e d = C r o s s h a t c h ,
Day
Intervals.
Control=Open
Block
PERCENT OF CALVES
f
••i----------—
O
n
-------------------------------------------------------------“
5
10
15
20
“
T ---------- ------------------------
25
30
—
i --------------------- ;-------------------------1-----------------------1
35
OAY OF C A L V I N G SEASON
40
45
SC
27
F i g u r e 4•
1976 T w o — Y e a r — O l d s Al S i r e d F i v e
_______________ T r e a t e d = C r o s s h a t c h ,
Control=Qpen
Bay Intervals.
B l o ck
PERCENT OF CALVES
in
O
5
I- - - - - - - I
I
I- - - - -
*, O
20
C5
i5
'
30
I
35
DAY OF C A L V I N G SEASON
40
45
50
28
the
control
group.
Table
2 illustrates
that a significant
difference (p < .05 ) occurs during days I 1-20 and 21-40 for Al
sired
calves.
Cumulative
effects
illustrate
a significant
difference during days 11-20 for Al sired calves.
Due to synchronization 77 percent of the treated calves
were born by day 20 versus 58 percent of the control calves.
Figure 5 illustrates the relationship of treated cows versus
control cows
occur
for percent calving at 5-day intervals.
for both
groups
at day 20
and
day 4 0.
Peaks
Although
difference is not significant due to synchronization
more treated
did
peak
but
for
genetic
(p>.05 )'
cows calved earlier in the calving season than
controls .
results
the
Control
the
peaks
controls
marker.
may
results
to
are not
as sharp.
be
to
Figure
5-day
tend
due
repeat
6 illustrates
intervals
Again
treated
the second
breeding
with
percent
Al
cows.
No treated calves were born during the first 5 days
20,
due
to
difference
For every 5 days after
synchronization,
born than controls.
versus
sired
during
day
treated
the
calves
of the calving season.
for
mirror
more
treated
control
day 5 up to
calves
were
This would account for the significant
(p . < 0 5 ) by
day
20
of
the
calving
s e aso n
illustrated in Table I.
1978 Results
Two hundred and fifty-two calves were born to treatment
and control cows during the 1978 calving season.
There were
Table 2
Influence of Day of Calving Season on Number of Cows Calving,
All
Days
1977
Cows
Al
of
Season
Treated
0-10
I 1-20
21-50
0-10
I I-20
n
days
days
days
n
days
days
143
13
64
66
I00
13
(13)
64
(64)3
23
(
23)
98
14
(14)
44
( 45 ) b
40
(
40)
100
13
(13)
77
(77)3
98
14
(14)
(11)
(46)
44
(34)
77
(54)
1 43
( 1 00 )
58
(44)
131
(100)
CO
14
(45)
=T
131
(9)
m
C-
Control
Sired
Ul
Calving
1977 (%)
21-40
C u m u l a t i ve
’ Means
numbers
14
within
(
9)
(11)
columns
bearing
different
superscripts
are
significantly
100
(100)
98
(100)
CT
131
13
CD
Control
143
Ul
Treated
CO
Effects
different
30
Intervals.
Line
PERCENT OF CALVES
F i g u r e 5•
1977 Cows Percent C a l v i n g F i v e - D a y
_______________T r e a t m e n t = S o l i d L i n e ,
C o n t r o l = D a sh
DAY OF C A L V I N G SEASON
Figure 6. 1977 Cows Al Sired Five-Day Intervals.
___________ Treated=Crosshatch, Control=Qpen B lock
PERCENT OF CALVES
in
in
D-
S-
S-
O
O5
10
20
25
30
35
DAY OF C A L V I N G SEASON
<
32
82
cows
in Treatment
I (T1) AILAIEt 86 in Treatment 2 (T2 )
LAIE and 84 Control (C) cows.
The length of the calving season in T 1 was 56 days, T2
was 46 days and C=52 days.
The mean day of calving was 22.2
days
for
for
T 1 , 20.7
Treatment
versus
affected
C only.
days
T2
the
mean
day
There
were
47 Al
and
of
25.3
calving
sired
days
for
C.
(p<.05 ) for
T2
calves
in T 1 (57
percent) , 45 in T2 (52 percent), and 32 in C (38 percent).
Table
3
illustrates
(p <. 05 ) occurred
for
Al
sired
percent
of
during
days
calves.
the
that
a
1-10
significant
difference
for
tested
Cumulative
T 2 calves
were
sired
born
by
show
day
and
that
31
10 versus
23
Cumulative effects for
calves show that 60 percent of the T2 calves were
born by day 10 versus 40 percent
C.
cows
effects
percent for T 1 and 14 percent for C .
Al
all
for T 1 and 50 percent for
Figure 7 illustrates treated versus control cows percent
calving at 5-day intervals.
A significant difference occurs
during
compared
group
days
has
decline.
peaks
to
when
another
T2 is
major
10, 20,
30,
at
and 45.
T 1 and T2 at day
at
suitable
day
30,
C
Figure
10,
mirrors
explanation
significant differences
5.
peak
to T 1 and
30
days
C„
then
The T2
starts
to
T 1 records peaks at days 10 and 20 while C records
at. days
both
while
1-5
for
but
T2 .
this
Peaks
for C are similar
at day 20 C mirrors T 1
I do
not
occurrence.
know
No
of
any
othe r
(p < .05 ) are noted other than days I-
8 illustrates, the
percent Al
sired
calves
born
Table 3
Influence of Day of Calving Season on Number of Cows Calving, 1978 (%)
Ml_Lll§._Cows
Al
D a y s of
Calving
Season
0-10
I 1-20
n
days
days
T 1
82
19
(23)3
28
(34 )
31
86
27
(3 I ) b
16
(19)
84
12
(14 ) c
23
82
19' ( 2 3 ) 3
T2
86
27
C
84 .
12
T2
C
.21-50
days
Sired
0-10
1 1-20
21-50
n
days
days
days
(38)
47
19
(40)3
25
(53)
3
(
6)
43
(50 )
45
27
( 6 0 ) b
14
(31 )
4
(
8)
(27)
47
(56)
22
II
(50)°
8
(36)
3
(
14 )
47
(57)
78
(95)
47
19
(40 ) a
44
(94 )
47
(100)
(31 ) b
43
(50)
86
(100)
45
27
( 6 0 ) b
4I
(91 )
45
(100)
(14)°
'35
(42)
82
(98)
22
II
(50)°
19
(86)
22
(100)
Cumulative
Effects
T1
a,t),GM e a n s
( p <,. 0 5 ) .
numbers
within
columns,
bearing
different
superscripts
are
significantly
different
34
PERCENT OF CALVES
Figure 7- 1978 Cows Percent Calving Five-Day Intervals.
T .=L arg e Da s h W i t h Ho u r Glasses, T o = Q m a l l Dash
___________ With Triangles, C=SoIid Line With Squares__________
DAY OF C A L V I N G SEASON
55
1978 Cows Al Sired Five-Day Intervals.
T1=Crosshatch, T2 =Open Block, C=Slash
PERCENT OF CALVES
Figure 8.
I
45
I
36
born
during
5-day
intervals.
The
highest
percentages
for
all three groups occur during days 6-10 with 45 percent for
percent
C , 35
significant
for
T 2 , and
(p<.05 ) occurs
for
T1 .
only
1-5 when
T2 (24 percent) was tested against T 1 (6 percent),
and C (4
A significant
difference
during
The
days
percent).
difference
3 4 percent
(pC.OI)
occured
during
days 16-20 for T 1 (35 percent) versus T2 (9 percent).
There
was not a significant difference (p<.05) when T 1 and T0 were
tested
ended
against
on
day
C during
30
and
days
no
other
16-20.
The Al calving season
significant
differences
were
noted.
Conclusions
Synchronization with PGF2c^will
a
producers
calving
season, but
affect many aspects of
will
it
cause
management
problems by having to many calves born early in the calving
season?
This
does
synchronization
synchronization
and
19 77
more
controls.
not
with
seem
to
be
PG F2ot. when
a major
problem
employing
systems used in this study.
synchronized
During
1976
cows
the
calved
the
due
to
types
of
During 1976
by day 20 than
difference
was
did
significant
(p< .05) for all mature cows and Al sired cows tested and for
all two-year-olds
was
a
(days
significant
11-2 0),
differences
and Al sired two-year-olds, tested.
difference
during
(p<.05 ) were
1 9 77 .
(p <.05 ) for
During
recorded
cows and for Al sired calves.
during
Al
19 7 8
days
sired
There
calves
significant
1-10
for
all
37
Synchronization with PGF2ck affected the mean day of the
calving
1976
season
mature
for
two
cows
and
of
significant
versus
non-synchronized
differences
difference was 3.8 days
tested„
first
calf
For
During
cows
both
synchronized
mature
cows
the
(T=24.5. versus 28.3 C ) and for two-
it
1978
in the T2 group
difference
6.4
years
(p< .05 ) for
animals.
year-olds
cows
three
two-year-old
showed
was
the
days
(1 =21.5
versus
(20.7 days)
27.9
showed
C ).
During
a significant
(p< .05) when tested against C (25.3 days) of 4.6
days.
Synchronization with PGF2cj4 only affected the length of
the
calving
year-olds
season
for one year.
completed
calving
During
in 52
days
1976 treated two-
versus
68
days
for
non-treated two-year-olds.
The
versus
numbers
of
Al
sired
non-synchronized
calves
cows
did
born
not
to
vary
synchronized
greatly.
The
largest difference recorded was 19 percent in 1978 for T 1 47
calves
(57 percent)
versus C 32 calves
(38 percent).
The
highest percentage of Al sired calves born in this study (75
percent)
was
for
calving season.
percentage
comparing
cows
during
the
1977
This was also the same year for the highest
of Al
70 percent.
non-synchronized
sired
calves
born
to synchronized cows at
Many variables must be taken into account when
number
of
Al
sired
calves.
Number
cycling, management, type of Al system used,
of
cows
and experience
of technicians are some important factors to consider.
38
Producers
wishing
to
utilize
system with Al should consider
of
the
system.
cycling
cows
They
to
Synchronization
obtain
will
the
breeding
season „
the
PGF2 ^ .
Even
born
earlier
in
must
the
PGFgoi synchronization
advantages and disadvantages
currently have
the
intensify
best
more
calving
a high
results
management
There will
though
a
number
with
and
labor
of
PGF2 ^ .
during
also be an added cost for
synchronized
season
the
calves
numbers
will
be
would
probably not be great enough to put a burden on the producer
during
calving.
If
producers
currently
have
a natural
breeding or Al system with relatively high conception rates
and
are
seasons,
for them.
satisfied
then
with
their
a synchronization
current
calving
system may not
rates
and
be suitable
39
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of
J.
M ONTANA STATE UNIVERSITY LIBRARIES
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