CSIRO PUBLISHING
Animal Production Science, 2009, 49, 619–623
www.publish.csiro.au/journals/an
Bovine somatotrophin stimulates milk production
in red deer hinds
G. K. Barrell A,D, J. A. Archer B, M. Wellby A, M. J. Ridgway A and M. J. Evans C
A
Agriculture and Life Sciences Division, PO Box 84, Lincoln University, Lincoln 7647, New Zealand.
AgResearch Invermay, Private Bag 50-034, Mosgiel 9053, New Zealand.
C
Endolab, Department of Endocrinology, Christchurch Hospital, Christchurch, New Zealand.
D
Corresponding author. Email: barrell@lincoln.ac.nz
B
Abstract. To determine its potential as a tool for studies of growth in suckling red deer calves, bovine somatotrophin
(bST) was administered to lactating red deer hinds. The present study used twice-daily machine milking of bST-treated hinds
(n = 10, 54 mg bST for 2 weeks then 108 mg for 1 week) and compared the milk yield with that of saline-treated controls
(n = 9). Treatment with 54 mg bST tended to increase milk yield by ~16% and the 108-mg dose increased (P = 0.013) milk
yield by ~32%. Both doses of bST increased (P < 0.05 and P < 0.001, respectively) plasma insulin-like growth factor-1
concentration but did not affect total solids or fat content of the milk, nor was there any effect on body condition score or
liveweight of the hinds. This shows that milk production in red deer hinds is increased by administration of bST, which makes
it a suitable experimental technique for investigating the lactational biology of red deer.
Introduction
There is a difficulty in differentiating between the genetic
potential of a mother to produce milk and the potential of the
offspring to obtain milk (Treacher 1983). The major non-genetic
factors involved in determining the level of milk production are
the level of nutrition of the mother and the demand for milk
from her offspring, as reflected by the level of suckling
stimulus (Treacher 1983; Rattray 1992). Other factors include
the number or genotype of fetuses that may influence the size of
the udder at birth (Treacher 1983) and udder (teat) performance
can limit the growth of offspring (Hammond et al. 1996).
Although suckling demand did not appear to elicit extra milk
production in guinea-pigs (Laurien-Kehnen and Trillmich 2003),
evidence from studies of sheep has shown major (20–50%)
increases in milk yield in ewes suckling twin lambs v. those
suckling singles, and even more (a further 15–20%) for ewes
suckling triplets (Treacher 1983; Rattray 1992; Morgan et al.
2007). This indicates that a ewe with a single lamb has
considerable potential for extra milk production that is not
utilised by the lamb and a similar case may apply to deer,
where there is usually a single calf. Support for this in deer
comes from red deer hinds suckling red or wapiti-red crossbred
calves where the latter calves had superior growth performance
(Asher et al. 2005; Ward et al. 2007) although, surprisingly,
there did not appear to be any difference in time spent suckling
(Ward et al. 2007). Overall, these findings in sheep and deer
indicate that, provided a mother is adequately nourished,
there is no point in increasing, or selecting for, her potential to
produce milk if the benefit is not utilised by the single offspring.
However, this is a fundamental concept that remains to be
determined for red deer.
To address this question, it will be necessary to develop an
experimental regime that can alter the milk output of red deer
CSIRO 2009
hinds, preferably without involvement of nutritional deficits.
Because of its ability to stimulate lactation in sheep
(Fernandez et al. 1995), goats (Disenhaus et al. 1995) and
cattle (Davis et al. 1999b), bovine somatotrophin (bST) was
administered to red deer hinds to investigate its effect in this
species. The hinds were machine milked to provide a standardised
stimulus to both treated and control animals.
Materials and methods
Animals
Animals included 20 mixed-age (4–11 years) red deer (Cervus
elaphus subspecies scoticus) hinds managed on the Deer Unit
of the Lincoln University Research Farm in Canterbury,
New Zealand. The hinds were grazed as a single mob on
pasture consisting of predominantly ryegrass and white clover,
with water available ad libitum. They were mustered into a
handling facility and blood sampling by jugular venepuncture
and injecting procedures were carried out by using manual
restraint in pens holding approximately five animals at a time.
Otherwise, hinds were placed into a side-loading mechanical
crush (Kean Deer Yards, Rangiora, New Zealand). They were
weighed with electronic scales (Model 700, Tru-Test, Auckland,
New Zealand) connected to load bars that supported the deer
crush. Body condition score was assessed on a scale of 0–5
(Audigé et al. 1998). On 9 January, calves were removed and
euthanased (at about Day 40 from birth) and thereafter,
commencing 10 January, the hinds were mustered from their
paddock and milked by machine twice per day (at 0700 hours and
1730 hours New Zealand Summer Time) for 3 weeks. All animal
procedures were approved by the Lincoln University Animal
Ethics Committee.
10.1071/EA08288
1836-0939/09/070619
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Animal Production Science
bST treatment
Before the commencement of bST treatment, hinds were
allocated to two groups (n = 10) balanced for liveweight, body
condition score and milk yield. Hinds in the treated group
received a single subcutaneous injection of 0.15 mL of a
suspension of zinc sometribove containing 54 mg of bovine
somatotrophin (Posilac, Monsanto, St Louis, MO, USA) in the
neck at commencement of the study and another injection of
108 mg bST 2 weeks later. Controls received an equivalent
volume of sterile 0.9% saline solution subcutaneously at the
same site on each occasion.
Milking procedure
Milk was extracted by machine, by using a similar procedure to
that described by Arman et al. (1974), except that only the rear
quarters of the udder were milked. Immediately before milking,
each hind received 1 mL intravenously of an aqueous solution
containing 10 IU of synthetic oxytocin (OxytocinEA, Ethical
Agents, South Auckland, New Zealand) and was then placed
in the crush. A milking machine (Duovac 300, Alfa-Laval,
Hamilton, New Zealand) set to a vacuum of 45 kPa was
connected to two single clear silicone rubber teat cups
(120 mm in length with an internal bore of 20 mm diameter,
Alfa-Laval Agri 988123-01, Alfa-Laval) that were inflated
intermittently (50 : 50 cycle) at 60 pulses per minute by a
pulsator. The cups were placed manually onto the two caudal
teats of the udder and milk was collected into a container. Once
the milk flow ceased, the cups were removed and the teats were
sprayed with dilute iodine solution (Vetadine Iodine Animal
Wash, Bomac Laboratories, Manakau City, New Zealand).
The volume of milk was recorded and a sample (~70 mL)
from each hind was transferred into a polypropylene storage
container and placed in a freezer (–20C) at the end of each
milking session. Milking sessions for the whole group typically
lasted ~100 min in total, although each hind was able to return
to pasture immediately on her release from the crush. One hind
in the control group that showed excessive loss of liveweight and
body condition was removed from the study after 1 week.
G. K. Barrell et al.
Plasma insulin-like growth factor-1 concentration
The concentration of insulin-like growth factor-1 (IGF-1) was
measured in plasma collected from all hinds on Days –1, 0
(the day of injection of 54 mg bST, sampled before injection),
1, 3, 7, 14 (the day of injection of 108 mg bST, sampled
before injection), and on Days 1, 3, 7 and 14 following
the day of injection of 108 mg bST.
For radioimmunoassay of IGF-1, plasma samples (100 mL)
were extracted by adding 400 mL of a mixture of hydrochloric
acid and ethanol (12.5 : 87.5% v/v) on ice, vortex mixing,
incubation for 30 min at 4C, then centrifugation for 15 min at
3000g at 4C. A 200-mL aliquot of the supernatant was added
to 80 mL of tris buffer (0.855 mol/L tris base), followed by
incubation for 60 min at –20 to –25C. After a further
incubation at 4C for 15–30 min, extracts were centrifuged
at 4C for 15 min at 2300g, then 100 mL of the supernatant
was added to 600 mL of assay buffer (0.05 mol/L phosphate
containing 0.05% alkali-treated casein). For the assay, 100 mL of
the diluted extract or human IGF-1 standards (receptor grade,
Novoenzymes GroPep, Adelaide, Australia) in assay buffer were
incubated with anti-human IGF-1 antiserum (1 : 6000,
Novoenzymes GroPep) together with an excess of IGF-2
(animal media grade, Novoenzymes GroPep) to bind any
residual IGF-binding proteins, and incubated overnight at
4C. IGF-1 (receptor grade, Novoenzymes GroPep) was radioiodinated by the chloramine-T method, with purification on
HPLC with acetonitrile and KH2PO4. After addition of 100 mL
125
I-IGF-1 in assay buffer and incubation overnight at 4C,
gammaglobulin (1.2% in assay buffer) was added and bound
radioactivity separated from free radioactivity by using 16%
polyethylene glycol 6000. After mixing and centrifugation for
15 min at 2300g at 4C, the supernatant was decanted and
radioactivity of the bound tracer counted. Bound counts (B)
were converted to a percentage of the counts bound (B0) in the
zero standard (i.e. B/B0 · 100) and plasma concentration (ng/mL)
was determined from the curve (Fig. 1) obtained by plotting
percentage B/B0 v. concentration of the human IGF-1 standard.
The intra-assay coefficient of variation was 10%. Serial
dilutions of cervine IGF-1 (kindly donated by Dr Lloyd Moore,
100
Human IGF-1
80
Cervine IGF-1
B/B0
Milk composition
Total solids (g/100 g) of milk were determined by weighing
~35 mL of each milk sample, lyophilising in a freeze-drier and
reweighing. Total lipids (mL/100 mL) were measured by a
modification of the creamatocrit method (Collares et al. 1997).
For this, 0.8 mL water and 0.4 mL of ammonium hydroxide
(28% w/w NH3) were added to 0.8 mL of each milk sample. The
mixture was warmed to 37C in a water bath, then transferred
to microhaematocrit capillary tubes (75 mm by 1.1 mm internal
diameter) in duplicate. The capillary tubes were centrifuged
at 14 000g for 15 min in a microhaematocrit centrifuge
(Haemofuge A, Thermo Fisher Scientific, Waltham, MA,
USA) and the lipid and aqueous layers measured with a
microhaematocrit reader. The value for the total lipids (v/v)
was converted to the weight/weight value by multiplying by
1.16, based on gravimetric data for bovine milk (Walstra et al.
2006).
Deer plasma 1
60
Deer plasma 2
40
20
0
5
10
15
IGF-1 (ng/mL)
Fig. 1. Standard curve for plasma insulin-like growth factor-1 (IGF-1)
concentration, showing parallelism of the human assay standard with
cervine IGF-1 and two serially diluted cervine plasma samples. B/B0 =
percentage counts bound/counts bound in the zero standard.
bST stimulates milk production in red deer hinds
(a)
1300
bST treated
Control
100
90
80
Condition score
4
54 mg bST
108 mg bST
621
108 mg bST
1100
1000
54 mg bST
900
800
700
600
(b)
500
8 Jan.
3
18 Jan.
13 Jan.
23 Jan.
28 Jan.
2 Feb.
Fig. 3. Daily milk yield (mean s.e.) of red deer hinds treated (arrows)
with bovine somatotrophin (bST) (n = 10) or saline (control, n = 9). Values
are means s.e. The area under the curve was higher (P = 0.013) for the
108-mg bST treatment.
2
1
8 Jan.
bST treated
Control
1200
Milk yield (mL)
Liveweight (kg)
110
Animal Production Science
15 Jan.
22 Jan.
29 Jan.
5 Feb.
Fig. 2. (a) Liveweight and (b) body condition score (scale 0–5) of lactating
red deer hinds that were treated (arrows) with bovine somatotrophin (bST)
(n = 10) or saline (control, n = 9). Values are means s.e.
AgResearch,NewZealand)andplasmasamplesfromdeershowed
parallelism with the human IGF-1 standard (Fig. 1).
Statistical analyses
Liveweight and body condition score data were analysed by twofactor ANOVA with replication. Area under the curve for the
daily milk yield data and loge-transformed plasma IGF-1
concentrations of each hind was calculated for the 2 weeks
following injection of 54 mg bST, and from Day –1 until
Day 6 in relation to injection of 108 mg bST. Differences in
the mean area under the curve between bST-treated and control
hinds were compared with Student’s t-test. Means s.e. are
reported.
after injection of 108 mg bST to treated hinds, mean daily milk
yield had increased to 1202 93.1 mL compared with
877 59.3 mL in control hinds.
Milk solids and milk fat
At the onset of machine milking, there was an initial increase in
total solids and lipid content of the milk (from 20.6 0.52% to
25.0 0.94% and from 8.0 0.70% to 10.9 0.73%, for total
solids and fat, respectively) and, thereafter, the values remained
relatively constant. There was no effect on milk composition
attributable to bST treatment of the hinds. Daily means for total
solids ranged from 23.3 0.48% to 25.7 1.18% and from
24.1 0.23% to 25.0 0.31% for hinds treated with 54 and
108 mg bST, respectively, and those for control hinds ranged
from 23.6 0.47% to 25.0 0.31%. Corresponding values for
lipid content were 8.3 0.68% to 10.4 0.90% and 8.7 0.76%
to 10.1 0.84% for hinds treated with 54 and 108 mg bST,
respectively, and 9.1 1.23% to 12.1 1.08% for controls.
Plasma IGF-1 concentration
Liveweight and body condition score
Mean liveweight and body condition score of all hinds fell slightly
during the first part of the study, then increased (Fig. 2), being
overall lower (P < 0.001 for liveweight and P = 0.016 for
condition score) in control hinds than in the bST-treated hinds.
Although both measures were slightly lower in control hinds
at its onset, control hinds appeared to suffer a slightly greater
loss of body condition than bST-treated hinds during the study
period (Fig. 2).
Milk yield
Treatment with bST produced a non-significant (P = 0.103),
although notable, increase (i.e. ~16%) in daily milk yield during
the 2 weeks following injection of 54 mg, and the 108-mg dose
produced a larger (~32%) and significant (P = 0.013) increase
during the following week (Fig. 3). At the onset of machine
milking, there appeared to be a temporary reduction of milk yield
in both groups (Fig. 3); thereafter, peak mean daily milk yields
in bST-treated and control hinds reached 974 101.7 mL and
801 60.8 mL, respectively, in the initial 2 weeks. Seven days
Mean plasma IGF-1 concentration increased from 75.6 8.48
to 118.8 13.90 ng/mL (P < 0.05) and to 295.8 25.48 ng/mL
(P < 0.001) at 24 h after 54 mg and 108 mg bST, respectively
(Fig. 4). Following treatment, the area under the curve for
500
Plasma IGF-1 (ng/mL)
Results
bST treated
Control
400
108 mg bST
300
54 mg bST
200
100
0
8 Jan.
13 Jan.
18 Jan.
23 Jan.
28 Jan.
2 Feb.
7 Feb.
Fig. 4. Plasma insulin-like growth factor-1 (IGF-1) concentration of
lactating red deer hinds treated (arrows) with bovine somatotrophin (bST)
(n = 10) or saline (control, n = 9). Values are means s.e. The area under the
curve was higher (P < 0.001) for the bST-treated hinds at both doses.
622
Animal Production Science
plasma IGF-1 concentration in bST-treated hinds was higher
than that in controls (P < 0.001, Fig. 4).
Discussion
These results show that the higher dose (108 mg) of bST
stimulated the production of milk in lactating red deer hinds
and thus provides a tool for investigating the importance of milk
yield on the growth of suckling young in this species.
Increase in plasma IGF-1 concentration is regarded as a
sensitive indicator of bST action in ruminants (Davis et al.
1987, 1999b; Breier et al. 1991) and the results for plasma
IGF-1 concentration are strong evidence that bST was
biologically active in these deer at both of the doses used in
the present study. Also, since IGF-1 is an important component
in the stimulatory action of bST on milk production in cows
(Molento et al. 2002), the increase in milk yield of the bST-treated
hinds recorded here can be partly attributed directly to the
elevated plasma IGF-1 concentrations recorded in bST-treated
hinds. This point was made in a similar study of bST-treated
lactating ewes that were also repeatedly machine milked
(Fernandez et al. 2001). In their study, Fernandez et al. (2001)
recorded dose-related increases in milk yield that were highly
correlated with plasma IGF-1 concentration.
The daily milk yields recorded here are ~25–50% lower than
those reported by others, e.g. Arman et al. (1974) and Loudon
et al. (1983, 1984) for Scottish red deer, Krzywinski et al. (1980)
for Polish red deer and Landete-Castillejos et al. (2000) for
Iberian red deer. However, the yields measured in the present
study were taken only from the caudal pair of teats and are
unlikely to represent the total production of the whole udder.
On the basis of regional differences in udder volume recorded
by Arman et al. (1974, caudal gland volume was 71% of the total
udder volume), the caudal glands would be expected to account
for the majority of the total milk output in red deer and this
has been confirmed by direct measurement of comparative
milk production (Landete-Castillejos et al. 2000, caudal glands
produced 61% of the total milk yield). Also, it is likely that nonremoval of milk from the cranial pair of quarters would have led to
cessation of secretion by these glands. The regular daily machine
milking of the caudal quarters may have shifted milk production
to this region of the udder, probably causing the steady increases
in milk yield recorded here. However, this may not have been
sufficient to match the full production potential of the whole
udder. Nevertheless, all hinds in the present study were milked in
a standardised manner, so the technique used here allows a direct
comparison of milk production to be made between the two
treatment groups. Thus, there can be no doubt about the
effectiveness of bST treatment in raising milk yield in these hinds.
Milk composition was similar to that recorded in other deer
studies (Arman et al. 1974; Krzywinski et al. 1980; LandeteCastillejos et al. 2000) for both total solids and lipid content and
did not appear to be influenced by the treatment of hinds with
bST. We were not able to measure protein levels in the present
study; however, data from an earlier study conducted by ourselves
(unpubl. data) showed no effect of bST treatment (108 mg per
hind fortnightly for 8 weeks) on protein levels in the milk
(7.9 0.28% and 8.0 0.21%, treated and control group,
respectively, n = 10). This is consistent with the results of
G. K. Barrell et al.
studies on the use of bST in other ruminants such as sheep
(Fernandez et al. 1995; Aaron et al. 1998; Sallam et al. 2005),
goats (Disenhaus et al. 1995; Davis et al. 1999a) and cattle
(Dohoo et al. 2003), in which effects on milk composition, if
significant, have been either inconsistent or very small. The initial
increase in total solids and lipid content of the milk might have
been a response of the mammary gland to greater emptying from
machine milking than from suckling.
Individual hind data for milk yield (not shown) indicated
that milk production in some animals did not respond to
stimulation by bST; hence, there was higher variability of the
mean values in the treated group (Fig. 3). A high variability in
milk yield response to bST in goats was recorded by Disenhaus
et al. (1995) who referred to other reports of such unexplained
individual variation in ruminants in their paper. It is interesting
that the higher milk yield following treatment of hinds with bST
was accomplished with a minimal reduction in body condition
score, which tended to be even less than that recorded in the
control hinds. This contrasts with the generally universal
reduction in body condition experienced by dairy cows under
bST treatment (Dohoo et al. 2003) and indicates that the treated
hinds may have increased their intake of feed to achieve the extra
milk yield without penalty in terms of body condition, unless the
treatment induced some fundamental increase in efficiency of
milk synthesis. Initially, there was a small reduction in liveweight
of both groups of hinds; however, this was followed by gain in
liveweight when milk yield was increasing. Throughout the
present study, the hinds were periodically moved to different
paddocks to ensure that the best available pasture was provided.
Therefore, it is not possible to determine the extent to which
changes in feed intake and/or feed quality may have influenced
these effects on liveweight and body condition score. Also, there
is a possibility that the hinds may have experienced some stress
from the experimental procedure, especially at the beginning, and
there was a minor, transient incidence of lameness in both groups
that could be attributed to the extra handling imposed by the study.
This condition responded well to antibiotic and anti-inflammatory
therapy, although one control-group hind displayed an excessive
loss of liveweight and a concomitant drop in milk production,
which resulted in her removal from the study after 1 week.
Acknowledgements
We thank Monsanto Co. (St Louis, MO, USA), especially Gregg Bogosian, for
generous donation of bST. Dr Lloyd Moore of AgResearch, New Zealand, is
thanked for his generous donation of cervine IGF-1. Omega Amoafo, Victoria
Barrell, Long Cheng, Alastair Nicol and Craig Trotter are thanked for their
help with the milking procedure. We are indebted to Alastair Nicol for his
knowledgeable advice on the conduct and interpretation of these studies. This
project was funded as a subcontract to AgResearch Contract C10X0202 from
the Foundation of Research, Science and Technology, New Zealand.
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Manuscript received 25 November 2008, accepted 17 February 2009
http://www.publish.csiro.au/journals/an