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Influence of feeding and diet on diurnal patterns of plasma
growth hormone and insulin in calves
Can. J. Anim. Sci. Downloaded from by on 10/24/17
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Mears, G. J. 1993.Influence of feeding and diet on diurnal patterns of plasma growth hormone
and insulin in calves. Can. J. Anim. Sci. 73: 987-991. Plasma GH concentrations were lower after
feeding than before (newborn calves, P < 0.05; steers, P < 0.01). Calves fed concentrate had higher
plasma insulin concentrations than those fed hay (P < 0.01). Meal feeding milk or concentrate, but
not hay, elevated plasma insulin (P < 0.05). Diet type and feeding time relative to sampling time must
be considered when measuring GH and insulin.
Key words: Diurnal patterns, growth hormone, GH, insulin, calves
Mears, G. J.1993.Influence du r6gime alimentaire et de la distribution des aliments par repas
sur I'6volution diurne des concentrations de GH et d'insuline chez les veaux. Can. J. Anim. Sci.
73:987-991. Les concentrations plasmatiques de GH 6taient plus basses aprbs le repas qu'avant (veaux
nouveaux-n6s P < 0,05; bouvillons P < 0,01). Les veaux recevant des concentr6s affichaient des
teneurs plasmatiques en insuline plus hautes que ceux qui consommaient du foin (P < 0,01). Le type
d'aliment et l'heure de la distribution par rapport )r I'heure des pr6ldvements sanguins doivent Otre pris
en compte dans les mesures des teneurs en GH et en insuline du plasma.
Mots cl6s: Evolution diurne. hormone de croissance. GH. insuline. veaux
The basal concentrations of circulatins
hormones in ruminants fluctuate due to i
number of intrinsic factors such as episodic
hormone release and diurnal rhythm. Other
factors such as ambient temoerature. diet and
feed intake can also influenie basal hormone
concentrations. Researchers measuring circulating hormones must consider the diurnal
patterns of concentrations of these hormones
and the effects of factors such as feedins and
diet on these patterns. Growth hormone fGH;
is released in an episodic manner in ruminants
resulting in peak plasma GH concentrations
every 1.3-2.0 h in Angus steers (Wheaton et
al. 1986). Superimposed on this pattern is a
diurnal rhythm (Ringberg 1978) that may
(Vasilatos and Wangsness 1980; Wheaton et
al. 1986) or may not (Chamley et al. 1974
Ringberg 1978) be influenced by meal
Plasma insulin concentrations in ruminants
also follow a diurnal pattern, which can be
markedly influenced by meal feeding
(Vasilatos and Wangsness 1980; Trenkle
Can. J. Anim. Sci. 73: 987-991 (Dec.
1981). Ruminants respond to high levels of
dietary grain or protein with greater concentrations of plasma insulin (Trenkle 1981), but
it is not known if the type of diet influences
the level of insulin response following meal
The objectives of this study were to determine the effects of diet and meal feedine on
diurnal GH and insulin patterns in
Five newborn Holstein bull calves (range
2-10 d old) and 15 Holstein steer calves
123-296 d old) were bled every 2 h
12-h period beginning at 07:00 h.
Newborn calves were bucket-fed mllk at l0%
of body weight (BW) at 08:00 and 15:00 h.
Steer calves were fed solid feed at 08:00 and
15:00 h, with all feed consumed within I h
of feeding on the day of this experiment.
Within each group of three calves at birth,
each calf was randomly assigned to one of
three dietary groups. After 100 kg BW they
received one of three diets: Diet 1, 85% grass
hay and 15% barley-based
Diet 2, same as diet
but with enough rumen
undegradable protein (formaldehyde-treated
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canola meal) added to raise the crude protein
content by 10 g kg-'; and Diet 3, 85%
barley-based concentrate and15% grass hay.
Calves were restricted-fed to 95% of estimated daily ad libitum feed intakes (for details
of feeding see Bailey (1989)). The amounts
of the three diets offered were designed to
provide equal qmounts of digestible energy
per unit BWU'/). The amounts of digestible
energy actually consumed were similar
(P > 0.1) for the three diets (Bailey 1989).
Calves were bedded on wood shavings in
individual pens in a heated barn with water
and trace-mineralized salts continuously avail-
in accordance with the
guidelines of the Canadian Council on Animal
able and handled
Blood samples were collected into
heparinized vacutainer tubes by jugular
venipuncture while gently restraining the
calves in their pens. The steers were also used
in another experiment in which they were frequently handled and sampled for blood. Consequently, they displayed little stress during
sampling for the present study, allowing all
samples to be collected during a 12- to 14-min
interval at each sampling time. Blood samples
were stored on ice between collection and centrifuging. Plasma was stored at -40'C until
assayed for GH and insulin using standard
double antibody homologous bovine radioimmunoassay (RIA) procedures (Mears et al.
1988). For the
(0.81 IU mg-1) was used as the reference
GH and for chloramine-T iodination, with
rabbit-antibovine GH, lot 3-28-VII (supplied
by the late Dr. I. Geschwind, University of
California, Davis, CA) as the primary GH
antibody. For the insulin RIA, bovine insulin
(I-5500. 26.8IU mg-r. Sigma St. Louis,
MO) was used as the reference insulin and for
chloramine-T iodination, with guinea pigantibovine insulin (65-101, Miles Laboratories, Elkhart, IN) as the primary insulin antibody. A11 samples were assayed in one RIA
for each hormone. Intra-assay coefficients of
variation were 6.2% for the insulin and7 .6%
for the GH RIA.
Mean plasma hormone concentrations for
the treatrnent groups were compared using the
SAS General Linear Model Procedure for
analysis of variance with time of collection
and treatment group (Newborns, Diet 1,
Diet2. Diet 3) as the main effects. When
there was a significantF (P < 0.05) for time
of collection the Student t test was used to
determine which collection time mean hormone concentrations were different from one
Plasma GH concentrations for steer calves
fed Diets 7 , 2 and 3 were similar (P > 0. 1)
and are pooled for presentation in Fig. 1.
They were much lower than those for newborn calves (P < 0.001). An effect of calf
age on plasma GH concentrations has previ-
ously been shown (Roy et al. 1983). Therefore, the higher plasma GH concentrations for
newborn calves were probably a result of their
younger age, rather than their milk diet. The
diurnal pattern of plasma GH concentration
for both newborn calves and steers was
influenced by meal feeding (Fig. 1). Plasma
GH concentrations were lower (P < 0.01) in
steers for all diets after both the morning and
afternoon feedings, as was found by Vasilatos
and Wangsness (1980) for Holstein cows,
Wheaton et al. (1986) for Angus steers, and
Trenkle (1989)
sheep. Newborn bull
(P < 0.05)
plasma GH concentrations after the morning milk feeding
with a trend (P < 0.1) towards lower concentrations at the time of the afternoon milk
feeding. The 15:00 h blood samples were
taken only a few minutes after the afternoon
feeding. As a result the next samples were
taken nearly 2 h after feeding. If the depression in GH concentration in newborn calves
was of short duration, as found by Bassett
(1914) for lambs only a few days old, it may
have been missed with our sampling schedule.
calves had lower
On the other hand, Ringberg (1978)
Driver and Forbes (1981) found
a depression
in GH concentration even before the afternoon
feedings for bull calves and sheep. The small
depression in plasma GH concentration in
newborn calves by the time of afternoon
feeding indicates that this may also have
occurred in the present study. A drop in
GH prior to feeding could be
accounted for by the involvement of neural
P- - -.q \
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g ,t2
Diets 1, 2, 3
Diets 1, 2
Diet 3
7:00 09:00
1 1
:00 13:00 15:00 17:00
Time of day (h)
1 . Plasma GH (upper panel) and insulin (lower panel) concentrations over a 12-h period for five
newborn Holstein bull calves fed milk and 15 Holstein steer calves fed Diets 1.2. and 3. Arrows indicate
times of feeding. Symbols indicate the probability of the values being different from the value obtained
prior to the last feeding ( o , P
> 0.05;
< 0.05; r , P <
pathways (Driver and Forbes 1981; Trenkle
no indication of a diurnal pattern and were
Plasma insulin patterns in newborn calves
demonstrated a meal feeding effect (Fig. 1)
pooled for presentation
feedings. A similar increase in plasma insulin
was reported for young lambs following milk
ingestion (Bassett 1974). Plasma insulin concentrations in steers fed Diets 1 and 2 save
born calves. By contrast, plasma insulin concentrations for steers fed high concentrate
Diet 3 were significantly (P < 0.01) higher
than those for Diets 1, ard2. and demonstrated
with elevated (P < 0.05) plasma insulin
concentrations following both daily milk
similar (P
> 0.1). Therefore they
in Fig. 1. Overall
mean plasma insulin concentrations for
Diets 1 and 2 were similar (P > 0.1) to the
overall mean insulin concentration for new-
a meal feeding effect with elevated plasma
insulin (P < 0.05) following both daily
feedings. This is similar to the reported effect
on plasma insulin concentrations of meal
Can. J. Anim. Sci. Downloaded from by on 10/24/17
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feeding high concentrate diets to mature cattle
and sheep (Vasilatos and Wangsness 1980;
Trenkle 1981). Elevated plasma insulin following milk ingestion in young ruminants
occurs as a result of absorbtion of carbohydrates as the end-products of digestion
(Bassett 1974). With the development of a
functional forestomach in older ruminants,
elevated plasma insulin following ingestion of
high concentrate diets occurs as a result of
circulating volatile fatty acids, the endproducts of digestion (Trenkle l98l). Lack
of an insulin response to meal feeding hay
diets in this study could be explained by the
slower ruminal digestion of roughage, which
in the rate of
In conclusion, these results clearly indicate
that type of diet and time of feeding must be
considered, along with the usual factor of
diurnal patterns of hormone release, when
planning experiments involving the measurement of GH and insulin. Depending on the
diet fed, meal feeding may play a major role
in altering the diurnal patterns of GH and
insulin concentration. Plasma GH concentrations are lower within 2 h of feeding either
hay or concentrate diets to steers. They are
also lower within 2 h of feeding milk to newborn calves, at least for the morning feeding.
Plasma GH may even begin
before the afternoon feeding in young calves.
Plasma insulin concentrations are higher in
calves fed a high concentrate as compared to
a high hay diet. Meal feeding of a milk or con-
products into the circulation and fail to stimu-
centrate diet elevates calf plasma insulin
late production of insulin.
The episodic release ofhormones, coupled
with infrequent blood sampling, may have
concentration, whereas meal feeding of a hay
diet does not. Therefore, samples for GH and
insulin determinations should be obtained at
the same time each day, relative to feeding
times. Also, calves should all be on the same
diet for measurement of plasma insulin, unless
diet is a variable in the experiment. Failure
to consider the effect that diet and the time
of feeding relative to time of sampling have
would modulate flow
influenced these results since the samples may
have been taken at any point from the peak to
the trough of a release. Although unlikely, such
fluctuations may have contributed to the lack
diet-generated differences observed for
plasma GH. However, an influence on the hormonal response to meal feeding was most likely
minimal, since meal feeding synchronizes
random episodic releases of GH in groups
on the diurnal pattern of GH and insulin
release may explain some reports of apparent
discrepancies in hormone levels.
1986). As the time
between feeding and sampling was uniform for
all calves in the present study, the effect ofepisodic release would be minimized. In our
experience. plasma insulin concentrations
exhibit little episodic release pattern in steers.
Technical assistance provided by F. A. Brown, calf
care provided by our animal herdsmen, the gift of
antisera to bovine GH by the late Dr. I Geschwind,
University of California, Davis, CA, and the gift
Hence, these results would be influenced very
little by the release pattern of insulin.
Plasma concentration of a hormone is the
Maryland School of Medicine, Baltimore, MD are
deeply appreciated.
steers (Wheaton et
net result of secretion into the circulatory
system minus clearance from the blood.
Decreased secretion of GH (Trenkle 1989)
and increased secretion of insulin (Bassett
1974; Trenkle 1981) occur following eating.
Therefore, the decrease in plasma GH and the
increase in plasma insulin following meal
feeding reported here are more likely due to
of NIH-GH-BI8 through the National Hormone
and Pituitary Program of NIDDK, University of
Bailey, C. B. 1989. Rate and efficiency of gain,
from weaning to slaughter, of steers given hay, hay
supplemented with ruminal undegradable protein,
or concentrate. Can. J. Anim. Sci. 69t 691-705.
Bassett, J. M. 1974. Early changes in plasma
insulin and growth hormone levels after feeding
in lambs and adult sheep. Aust. J. Biol. Sci. 27:
Chamley, W.A., Fell, L. R., Alford, F. P. and
Goding, J. R. 1974. Twenty-four hour secretory
profiles of ovine prolactin and growth hormone.
J. Endocrinol. 61: 165-166.
Trenkle, A. 198f. Endocrine regulation ofenergy
Driver, P. M. and Forbes, J. M. 1981. Episodic
growth hormone secretion in sheep in relation to
hormone-releasing factor in sheep. J. Nutr. 119:
time of feeding, spontaneous meals and short term
fasting. J. Physiol. 317: 413-424.
Can. J. Anim. Sci. Downloaded from by on 10/24/17
For personal use only.
Mears, G. J., Vesely, J. A. and Cheng, K.-J.
L988. Plasma insulin and growth hormone in
growing lambs fed monensin. Can. J. Anim. Sci.
68: 165-171.
Ringberg, T. 1978. Diurnal variation of growth
hormone in bull calves. Acta Agric. Scand. 28:
Roy, J. H. B., Hart, I. C., Gillies, C. M., Stobo,
I. J. F., Ganderton, P. and Perfitt, M. W. 1983.
A comparison of preruminant bull calves of the
Hereford x Friesian, Aberdeen Angus x Friesian
and Friesian breeds. Plasma metab-olic hormones
in relation to age, and the relationship of metabolic
hormone concentration with dry-matter intake and
heart rate. Anim. Prod. 36:237-251.
metabolism in ruminants. Fed. Proc. N: 2536-2541.
Trenkle, A. 1989. Influence of feeding on growth
hormone secretion and response
R. and Wangsness, P.
Changes in concentrations ofinsulin, growth hormone and metabolites in plasma with spontaneous
feeding in lactating dairy cows. J. Nutr. 110:
Wheaton, J, E., Al-Raheem, S. N., Massri,
Y. G. and Marcek, J. M. 1986. Twenty-fourhour growth hormone profiles in Angus steers.
J. Anim. Sci. 62: 1267-12'12.
G. J.Mears
Reseorch Stqtion, Agriculture Canada, P.O.
Box 3000, Main, Lethbridge, Alberta,
Canada TI J 481. Contibution no. 3879284,
received 4 January 1993, accepted 12 July
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