#736
Proceedings, Western Section, American Society of Animal Science
Vol. 63, 2012
PLASMA PROGESTERONE CONCENTRATION IN BEEF HEIFERS RECEIVING EXOGENOUS GLUCOSE,
INSULIN, OR BOVINE SOMATOTROPIN
B. I. Cappellozza1, R. F. Cooke1, M. M. Reis2, F. N. T. Cooke1, D. W. Bohnert1, and J. L. M. Vasconcelos2
1
Oregon State University - Eastern Oregon Agricultural Research Center, Burns; and
2
UNESP – FMVZ/DPA, Botucatu, SP, Brazil
ABSTRACT: Three experiments evaluated plasma
concentrations of glucose, insulin, IGF-I, and progesterone
(P4) in pubertal beef heifers receiving exogenous glucose,
insulin, or sometribove zinc. All heifers utilized had no luteal
P4 synthesis but received a controlled internal drug releasing
device containing 1.38 g of P4 to estimate treatment effects
on hepatic P4 degradation. In Exp. 1, 8 nulliparous Angus
× Hereford heifers (initial BW = 442 ± 14 kg; initial age =
656 ± 7 d) were randomly assigned to receive, in a crossover
design containing 2 periods of 10 h: 1) intravenous (i.v.)
insulin infusion (1 μg/kg of BW; INS) or 2) i.v. saline infusion
(0.9%; SAL). Treatments were administered via jugular
venipuncture in 7 applications (0.15 μg of insulin/kg of BW
per application) 45 min apart (from 0 to 270 min). Blood
samples were collected immediately before each infusion,
as well as at -120, -60, 330, 390, and 450 min relative to the
first infusion. Heifers receiving INS had greater (P < 0.01)
plasma insulin, reduced (P ≤ 0.04) plasma glucose and IGF-I,
but similar (P = 0.62) plasma P4 concentrations compared
with SAL heifers. In Exp. 2, the same heifers were assigned
to receive, in a similar experimental design as Exp. 1: 1) i.v.
infusion containing insulin (1 μg/kg of BW) and glucose (0.5
g/kg of BW; INS+G) or 2) SAL. Heifers receiving INS+G
had greater (P ≤ 0.02) plasma insulin, glucose, and P4, but
reduced (P = 0.01) plasma IGF-I concentrations compared
with SAL heifers. In Exp. 3, the same heifers were assigned to
receive, in a crossover design containing 2 periods of 14 d:
1) subcutaneous injection containing 250 mg of sometribove
zinc (BST), or 2) SAL. Blood samples were collected 3
h apart (from 0900 to 1800 h) on d 6, 8, and 10 relative to
treatment administration (d 1). Heifers receiving BST had
greater (P < 0.01) plasma glucose and IGF-I, and similar
(P ≤ 0.67) plasma insulin and P4 concentrations compared
with SAL heifers. Results from this series of experiments
suggest that concurrent increases in glucose and insulin
are required to reduce hepatic catabolism and increase
plasma concentrations of P4 in bovine females.
demonstrate that energy intake can be positively associated
with hastened attainment of puberty, decreased postpartum
interval, and greater pregnancy rates (Wiltbank et al.,
1962; Schillo et al., 1992; Pescara et al., 2010). Moreover,
beneficial effects of energy intake on cattle reproduction
are regulated, at least partially, by circulating hormones and
metabolites such as glucose, insulin, and IGF-I (Wettemann
et al., 2003).
As an example, insulin modulates circulating
concentrations of progesterone (P4; Lopes et al., 2009),
a steroid required for resumption of estrous cycles and
establishment and maintenance of pregnancy (Looper et al.,
2003). More specifically, insulin stimulates luteal P4 synthesis
(Spicer and Echternkamp, 1995) and alleviates hepatic steroid
catabolism (Lemley et al., 2008). Our research group recently
reported that cows in adequate nutritional status receiving
intravenous (i.v.) glucose infusion to increase circulating
insulin concentrations had greater plasma P4 concentrations
compared with cohorts receiving saline, which was attributed
to reduced hepatic P4 degradation given that cows were
ovariectomized and supplemented with exogenous P4
(Vieira et al., 2010). However, glucose supplementation
also increases circulating concentrations of other hormones
associated with reproductive and hepatic functions, including
glucose itself and IGF-I (Jones and Clemmons, 1995).
Therefore, we hypothesized that the insulin- stimulated
decrease in hepatic P4 catabolism may also be dependent
on circulating glucose and IGF-I. Based on this rationale, 3
experiments were conducted to evaluate plasma concentrations
of glucose, insulin, IGF-I, and P4 in beef females receiving
exogenous insulin, insulin + glucose, or ST.
Materials and Methods
Animals utilized were cared for in accordance with
acceptable practices and experimental protocols reviewed and
approved by the Oregon State University, Institutional Animal
Care and Use Committee. All experiments were conducted at
the Oregon State University – Eastern Oregon Agricultural
Research Center (Burns, OR) from January to March 2011.
Experiment 1. Eight pubertal, nulliparous Angus x
Hereford heifers (initial BW = 452 ± 12 kg; initial age = 656
± 7 d) were assigned to an estrus synchronization protocol
(d -16 to 0 of the study). On d -16 heifers received a 100-µg
treatment of GnRH (Cystorelin, Merial Ltd., Duluth, GA)
and a controlled internal drug releasing device containing
Key words: beef heifers, glucose, insulin-like growth factor-I,
insulin, progesterone
Introduction
Nutrition, more specifically energy intake, is the
environmental factor that most influences reproductive
function in beef females (Mass, 1987). Several studies
225
1.38 g of P4 (CIDR, Pfizer Animal Health, New York, NY),
PGF2α treatment (25 mg Lutalyse, Pfizer Animal Health) and
CIDR removal on d -9, and a second GnRH treatment (100
µg) on d -7. On d 0, heifers received another PGF2α treatment
(25 mg) and a CIDR that remained in heifers throughout Exp.
1 (d 0 to 14). Transrectal ultrasonography examinations were
performed immediately and 48 h after the second GnRH (d 7) and PGF2α (d 0) treatments to verify ovulation and corpus
luteum (CL) regression, respectively. All heifers utilized in this
experiment responded to the hormonal treatment.
Heifer BW was recorded at the beginning and end of
the experiment (d 0 and 14). On d 5, heifers were randomly
assigned to receive, in a crossover design containing 2 periods
of 10 h each (d 6 and 8): 1) i.v. insulin infusion (1 µg/kg of
BW; INS), or 2) i.v. saline infusion (0.9%; SAL). Bovine
insulin solution was dissolved into 10 mL of physiological
saline immediately prior to infusions and administered via
jugular venipuncture in 7 applications (0.15 µg/kg of BW
per application) 45 min apart (0, 45, 90, 135, 180, 225, and
270 min), whereas SAL heifers concurrently received 10
mL of physiological saline. Blood samples were collected
immediately before each infusion, as well as at -120, -60,
330, 390, and 450 min relative to the first infusion. All
heifers were fasted for 12 h prior to the beginning of each
period, and remained fasted during sampling, to prevent
any confounding effects between feed intake and infusion
treatments on circulating concentrations of P4 (Vasconcelos
et al., 2003).
Experiment 2. Immediately after the end of Exp.1 (d
14), the same heifers (mean BW = 456 ± 14 kg) received a
new CIDR and evaluated via transrectal ultrasonography to
confirm the absence of a CL.
Heifer BW was recorded at the beginning and end of
the experiment (d 14 and 28). On d 20, heifers were randomly
assigned to receive, in a crossover design containing 2 periods
of 10 h each (d 20 and 22): 1) i.v. infusion containing insulin
(1 µg/kg of BW) and glucose (0.5 g/kg of BW; INS+G), or 2)
i.v. saline infusion (0.9%; SAL). Glucose and bovine insulin
solution were dissolved into 10 mL of physiological saline
immediately prior to infusions. Similarly to Exp. 1, infusion
was administered via jugular venipuncture in 7 applications
(0.07 g/kg and 0.15 µg/kg of BW per application for glucose
and insulin, respectively) 45 min apart. Blood samples were
collected immediately before each infusion, as well as at -120,
-60, 330, 390, and 450 min relative to the first infusion. As in
Exp. 1, heifers were fasted for 12 h prior to the beginning and
during the sampling.
Experiment 3. Immediately after the end of Exp. 2 (d
28), heifers (mean BW = 462 ± 14 kg) received a new CIDR
and were evaluated via transrectal ultrasonography to confirm
the absence of CL.
Heifer BW was recorded at the beginning and end of
the experiment (d 28 and 55). On d 28, heifers were randomly
assigned to receive, in a crossover design containing 2 periods
of 14 d each (d 28 to 42 and 42 to 56): 1) s.c. injection
containing 250 mg sometribove zinc (BST; Posilac, Elanco,
Greenfield, IN), or 2) subcutaneous (s.c.) saline injection
(0.9%; SAL). Treatments were applied once, at 0800 h, during
the first day of each period (d 28 and 42). Heifer also received
a new CIDR at the beginning of the second period concurrently
with treatment administration (d 42).
Four blood samples were collected, 3 h apart (from 0900
to 1800 h) from heifers on d 33, 35, and 37 (period 1) and
47, 49, and 51 (period 2) of the experiment. Similarly to Exp.
1 and 2, all heifers were fasted for 12 h prior to the beginning
and during each collection day.
Diets. During all experiments, all heifers were individually
offered (as-fed basis) 12 kg of mixed alfalfa- grass hay, 1.0 kg
of ground corn, and 0.5 kg of camelina meal in the morning
(0700 h). Heifers also received a complete commercial mineral
and vitamin mix and water for ad libitum consumption.
Blood Analysis. All blood samples were harvested for
plasma and stored at −80°C until assayed for concentrations
of glucose (#G7521; Pointe Scientific, Inc., Canton, MI),
insulin (B1009; Endocrine Technologies Inc., Newark, CA),
IGF-I (SG100; R&D Systems, Inc., Minneapolis, MN), and P4
(11-PROHU-E01; Alpco Diagnostics, Salem, NH).
Statistical Analysis. All data were analyzed using
the PROC MIXED procedure (SAS Inst. Inc., Cary, NC) and
Satterthwaite approximation to determine the denominator
degrees of freedom for the tests of fixed effects. Heifer was
considered the experimental unit for all analysis. The model
statement used for Exp. 1 and 2 contained the effects of
treatment, time, the resultant interaction, in addition to period
as independent variable. Data obtained prior to treatment
application (-120, -60, and 0 min prior to infusion) were averaged
and used as covariate. Heifer was used as random variable. The
specified term for the repeated statement was time, and heifer
(treatment × period) was included as subject. The covariance
structure utilized was autoregressive, which provided the lowest
Akaike information criterion and hence the best fit for all
variables analyzed. Results are reported as covariately adjusted
least square means if the covariate was significant (P ≤ 0.05),
and were separated by LSD. The model statement used for Exp.
3 contained effects of treatment, day, time, and all interactions,
in addition to period as independent variable. Heifer was
used as random variable. The specified term for the repeated
statement was time, and heifer (treatment × day × period)
was included as subject. The covariance structure utilized was
autoregressive, which provided the lowest Akaike information
criterion and hence the best fit for all variables analyzed. Results
are reported as least square means and separated using LSD.
For all analysis, significance was set at P ≤ 0.05 and tendencies
were determined if P > 0.05 and ≤ 0.10. Results are reported
according to treatment effects if no interactions were significant
or according to highest-order interaction detected.
Results and Discussion
Experiment 1. Heifer BW did not change (P = 0.51; data
not shown) during the experimental period, indicating that
heifers were in adequate nutritional status. As expected,
mean plasma insulin concentration during the experimental
period was greater (P < 0.01) for INS compared with SAL
(Table 1).
226
(Lemley et al., 2008) and resultant plasma P4 concentrations
(Vieira et al., 2010) included glucose infusion into the
experimental design.
!
!
!
!
!
90.0
A treatment × time interaction was detected (P = 0.01) !
!
!
!
!
85.0
!
**
for plasma glucose (Figure 1). After the initial infusion,
** **
!
!
**
*
**
**
plasma glucose decreased for INS heifers (time effect; P <
!
80.0
*
!
0.01) and did not change for SAL heifers (time effect; P = !
75.0
!
0.53). Moreover, mean plasma glucose concentration during !
!"#$
70.0
the experimental period was reduced (P < 0.01; Table 1) !
%&!!
65.0
for INS compared with SAL heifers. In agreement, Kegley
!
et al. (2000) also reported that i.v. insulin infusion reduced
60.0
circulating glucose concentrations in beef cattle, given that !
55.0
insulin directly estimates the uptake of glucose by body !
50.0
tissues (Nelson and Cox, 2005).
45
90
135
180 225 270
330 390 450
Mean plasma IGF-I concentration was reduced (P =
Minutes relative to first treatment infusion
0.04) for INS heifers compared with SAL heifers during the
Figure 1. Plasma glucose concentrations of heifers receiving
experimental period (Table 1). The goal of Exp. 1 was to
Figure
1. Plasma
glucose concentrations
of heifers receiving
i.v. infusions
containing
10 mL of physiological
saline
evaluate if insulin administration would increase plasma P4
i.v.
infusions
10 mL
of physiological
salineA
(0.9%;
SAL) containing
or 0.15 !g/kg
of BW
of insulin (INS).
concentrations in beef heifers in adequate nutrient balance, by
interaction
wasBW
detected
(P < (INS).
0.01).
treatment
" time
(0.9%;
SAL)
or 0.15
µg/kg of
of insulin
reducing hepatic P4 catabolism, independently of circulating
Treatment
within time:
** detected
P < 0.01,(P
* P<= 0.01).
0.01.
A
treatmentcomparison
× time interaction
was
concentrations of glucose and IGF-I. However, no treatment
Similarly
to PExp.
1, BW
not
TreatmentExperiment
comparison 2.
within
time: **
< 0.01,
* P =did
0.01.
effects were detected (P = 0.62) for plasma P4 concentrations
change (P = 0.55; data not shown) during the experimental
(Table 1). Therefore, insulin itself may not be capable of
period. As expected by the experimental design, mean
IGF-I,
IGF-I
alsoinsulin
influences
hepatic functionduring
and could
alleviating hepatic P4 catabolism and consequently increasing
plasmawhereas
glucose
and
concentrations
the
potentially
modulate
hepatic
steroid
catabolism
(Jones
and
circulating concentrations of this hormone. Accordingly,
experimental period were greater (P # 0.01) for INS+G
Clemmons,
1995).
Nevertheless,
results
fromhad
Exp.
2 suggest
research
studies
the role ofwith
insulin
hepatic
(P < 0.01;
Tabledocumenting
1) for INS compared
SALon
heifers.
In
to
Exp. 1,(Table
INS+G
heifers
reduced
(P
comparedSimilarly
with
SAL
heifers
2).
that
i.v.
insulin
infusion
increased
plasma
P
concentrations
expression
of
P
catabolic
enzymes
(Lemley
et
al.,
2008)
agreement, Kegley
et al. (2000) also reported that i.v. insulin
= 0.01) mean plasma IGF-I concentrations 4compared with
4
by
reducing
hepaticthe
P4 experimental
catabolism only
when
supplemental
and
resultant
plasma
P4 concentrations
(Vieira et al.,in2010)
infusion
reduced
circulating
glucose concentrations
beef
SAL
heifers during
period
(Table
2). Other
glucose
is provided.
results
from Exp.
2 combined
included
glucose
infusion
the experimental
design.
cattle, given
that
insulininto
directly
estimates the
uptake of
researchers
reportedTherefore,
that cattle
receiving
i.v infusion
of
glucose
by body 2.
tissues
(Nelson
and Cox,
2005).
insulin
andreported
glucosebyhad
similar
2002)
with
those
Lemley
et (Molento
al. (2008) et
andal.,Vieira
et or
al.
Experiment
Similarly
to Exp.
1, BW
did not change
!(P = 0.55; data not shown) during the experimental period. As
greatersuggest
circulating
IGF-I concentrations
compared
with
(2010)
that circulating
glucose modulates
the effects
of
Table 1.byPlasma
concentrations
of glucose,
insulin,glucose
IGF-I,
cohortson
receiving
saline (Butler
et al.,
insulin
hepatic steroid
catabolism
and2003).
subsequent circulating
expected
the experimental
design,
mean plasma
During the
period,
INS+G heifers
had
andinsulin
p r o g econcentrations
s t e r o n e ( P4during
) in beef
receiving
i.v.
P4 concentrations
in experimental
bovine females
in adequate
nutritional
and
the heifers
experimental
period
greater (P = 0.02) mean P4 concentration compared with
infusion
of insulin
(1!g/kg
BW; INS;
n = 8)with
or saline
status.
were
greater
(P ≤ 0.01)
for of
INS+G
compared
SAL
SALExperiment
heifers (Table
The goal
Exp.
was2,toBW
evaluate
if
(0.9%;(Table
SAL; 2).
n = 8) in Exp. 1
3. 2).
Similarly
to of
Exp.
1 2and
did not
heifers
supplemental
glucose
modulates
the
effects
of
insulin
change (P = 0.72; data not shown) during the experimental
Similarly to Exp. 1,INS
INS+G SAL
heifers had
Item
SEMreduced
P =(P =
infusionAs
on expected,
plasma P4 BST
concentrations
by greater
reducing(Phepatic
P4
period.
heifers had
< 0.01)
0.01) mean plasma IGF-I concentrations compared with
Glucose, mg/dL
68.20
79.00
1.30
< 0.01
catabolism.
In
fact,
we
also
expected
that
INS+G
heifers
mean plasma IGF-I concentrations compared with
SAL heifers during the experimental period (Table 2).
would have greater plasma IGF-I, whereas IGF-I also
Insulin,
ng/mL reported
1.40that cattle
0.99 receiving
0.10 i.v <infusion
0.01
SAL heifers (Table 3), given that sometribove zinc has
Other
researchers
influences hepatic function and could potentially modulate
been
shown to increase IGF-I synthesis and circulating
of IGF-I,
insulinng/mL
and glucose145.00
had similar
(Molento
2002)
hepatic steroid catabolism (Jones and Clemmons, 1995).
154.00
3.00et al.,0.04
or greater circulating IGF-I concentrations compared with
concentrations
in cattlefrom
(Bilby
et al.,
1999). Heifers
Nevertheless, results
Exp.
2 suggest
that i.v.receiving
insulin
3.74 et 3.84
0.65
P4, ng/mL
cohorts
receiving saline (Butler
al., 2003).0.27
BST
had increased
greater (Pplasma
< 0.01)
glucosebybutreducing
similar
infusion
P4 plasma
concentrations
During the experimental period, INS+G heifers had greater
(P
= 0.76)
plasma insulin
concentrations
compared
!
only when
supplemental
glucosewith
is
hepatic
P4 catabolism
(P = 0.02)Mean
mean plasma
P4 concentration
compared with
heifers
IGF-I concentration
was SAL
reduced
(P
SAL
heifers
(Table 3).
In the
present
the increase
provided.
Therefore,
results
from
Exp. study,
2 combined
with
(Table
2).for
The
goal1)
offorExp.
2 compared
was to with
evaluate
if heifers
supplemental
= 0.04)
INS
heifers
compared
SAL
during
(P
< 0.01;
Table
INS
with
SAL
heifers.
In
Similarly
Exp. 1, et
INS+G
heifers
had
reduced
in
plasma
glucose
concentrations
in BST
heifers
despite
those
reported
bytoLemley
al. (2008)
and
Vieira
et(Pal.
the experimental
period
(Table
1). reported
The
goalthat
ofonExp.
1 was
agreement,
Kegleythe
et al.
(2000)
also
i.v.
insulin
=similar
0.01) suggest
mean plasma
IGF-I concentrations
compared
with
glucose
modulates
effects
of insulin
infusion
plasma
P4
insulin
concentrations
can
be attributed
tothe
decreased
(2010)
that circulating
glucose
modulates
effects
to evaluate
if by
insulin
administration
would increase
infusion
reduced
circulating
glucose
inplasma
beef
SAL
heifers
during
the
experimental
period
(Table
2).
Other
concentrations
reducing
hepatic
P4 concentrations
catabolism.
In fact,
we
of
insulin
on
hepatic
steroid
catabolism
and
subsequent
insulin sensitivity caused by sometribove zinc administration
P4 expected
concentrations
in beef
heifers
inhave
adequate
nutrient
cattle,
given that INS+G
insulin
directly
estimates
the
uptake
of
researchers
reported
receiving
i.v infusion
of
circulatingetP
in bovine
females
in adequate
also
heifers
would
greater
plasma
4 concentrations
(Dunshea
al.,
1995).that cattle
balance,byby
reducing
glucose
body
tissues hepatic
(Nelson Pand
Cox, 2005).independently
insulin
and status.
glucose had similar (Molento et al., 2002) or
4 catabolism,
nutritional
! of circulating concentrations of glucose and IGF-I. However, greater
circulating IGF-I concentrations compared with
!
no treatment
effects
were detected
= 0.62)insulin,
for plasma
P4
Table
1. Plasma
concentrations
of (P
glucose,
IGF-I,
cohorts
(Butler et al.,
2003). insulin, IGF-I,
Table receiving
2. Plasmasaline
concentrations
of glucose,
concentrations
insulin receiving
itself may i.v.
not
During
the
experimental
period,
INS+G i.v.
heifers
had
and
p r o g e s t e(Table
r o n e 1).
( P4Therefore,
) in beef heifers
infusion
and progesterone (P4) in beef heifers receiving
be capable
of alleviating
P4 ncatabolism
and
compared
withof
greater
(P insulin
= 0.02)(1mean
infusion
of insulin
(1!g/kg of hepatic
BW; INS;
= 8) or saline
4 concentration
containing
!g/kg Pof
BW) and glucose
(0.5 g/kg
consequently
concentrations of this
SAL
of Exp.
(0.9%;
SAL; n increasing
= 8) in Exp.circulating
1
BW;heifers
INS+G;(Table
n = 8)2).
or The
salinegoal
(0.9%;
SAL;2 nwas
= 8)toinevaluate
Exp. 2 if
hormone. Accordingly, research studies documenting the
supplemental
glucose
modulates
the
effects
of
insulin
Item
INS
SAL
SEM
P=
Item
INS+G
SAL
SEM
P=
role of insulin on hepatic expression of P4 catabolic enzymes
infusion on plasma P4 concentrations by reducing hepatic P4
(Lemley
al., 2008) and
resultant
plasma1.30
P4 concentrations
Glucose,etmg/dL
68.20
79.00
< 0.01
catabolism.
In fact, we
also expected
INS+G0.01
heifers
Glucose, mg/dL
133.90
76.80 that
16.40
(Vieira et al., 2010) included glucose infusion into the
would have greater plasma IGF-I, whereas IGF-I also
Insulin, ng/mL
1.40
0.99
0.10
< 0.01
Insulin, ng/mL
3.65
2.12
0.32
< 0.01
experimental design.
influences hepatic function and could potentially modulate
! IGF-I, ng/mL
hepatic
and Clemmons,
1995).
145.00 154.00
3.00
0.04
IGF-I, steroid
ng/mL catabolism
134.00(Jones
142.00
2.00
0.01
!
!
!
!
!
90.0
Nevertheless,
results from Exp. 2 suggest that i.v. insulin
!
!
! P4, ng/mL
! 0.27
3.74
0.65 !
2.88 P concentrations
2.52
0.11 by reducing
0.02
P4, ng/mL
! 3.84
infusion
increased plasma
4
!
85.0
!
**
** **
!
!
!
**
hepatic
P4 catabolism only when supplemental glucose is
!
*
**
**
!
80.0
*
Mean plasma
IGF-I concentration was reduced (P
Experiment
Similarly
Exp.21 combined
and 2, BWwith
did
provided.
Therefore, 3.
results
from toExp.
!
!
75.0for INS heifers compared with SAL heifers during 227those
= 0.04)
reported
by
Lemley
et
al.
(2008)
and
Vieira
et
al.
not
change
(P
=
0.72;
data
not
shown)
during
the
!
!
the experimental
period (Table 1). The goal of Exp. 1 was
!"#$
(2010)
suggestperiod.
that circulating
glucose
modulates
the effects
experimental
As expected,
BST
heifers had
greater
70.0
! to evaluate if insulin administration would increase plasma
%&!!
of(P insulin
hepatic
steroid
catabolism
and subsequent
< 0.01)onmean
plasma
IGF-I
concentrations
compared
65.0
P concentrations
in beef heifers in adequate nutrient
Glucos
Insulin
IGF-I,
! P4, ng/m
!
!
!
not cha
experim
(P < 0.
with SA
been sh
concentr
receiving
similar (
with SA
increase
despite
decrease
administ
circulati
consequ
directly
Clemmo
were sim
(Table 3
!
!
!
!
!
!
catabolism in bovine females in adequate nutritional status
is not directly regulated by circulating IGF-I.
Table 3. Plasma concentrations of glucose, insulin, IGF-I,
and P4 in beef heifers receiving s.c. injection containing 250
mg sometribove zinc (BST; n = 8) or saline (0.9%; SAL; n =
8) in Exp. 3.
Item
BST
SAL
SEM
P=
Glucose, mg/dL
73.00
69.60
1.60
< 0.01
Insulin, ng/mL
1.44
1.65
0.51
0.76
IGF-I, ng/mL
248.00
143.00
6.00
< 0.01
3.07
3.13
0.15
0.67
P4, ng/mL
Implications
The main goal of Exp. 3 was to determine if circulating
Results
collectively
suggest
that the
effects of
IGF-I also
modulates
hepatic P
and consequent
4 catabolism
insulin
on hepatic
P4 that
degradation
anddirectly
circulating
P4
P
given
this hormone
regulates
4 concentrations
concentrations
in bovine
in adequate
hepatocytes
activity
(Jones females
and Clemmons,
1995).nutritional
However,
statusplasma
are dependent
on circulating
glucose,
notbetween
IGF-I.
mean
P4 concentrations
were similar
(P =but
0.67)
In addition,
results
reported
indicate that
BST
and SAL
heifers
(Tableherein
3), suggesting
that nutritional
hepatic P4
alternatives in
to bovine
increasefemales
circulating
concentrations
of glucose
catabolism
in adequate
nutritional
status
and
insulin
may
benefit
reproductive
function
of
females
in
is not directly regulated by circulating IGF-I.
adequate nutritional status by increasing circulating
concentrations of P 4.
Implications
!
Results collectively
suggest that
the effects of insulin on
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