ISRAEL JOURNAL OF
VETERINARY MEDICINE
PLASMA INSULIN CONCENTRATIONS AND
THYROID HORMONE IN FED AND UNDERFED BOER
GOAT BUCKS
A. M. Almeida1, L. M. Schwalbach2, H. O. deWaal2, J. P.
Greyling2 and L. A. Cardoso1
Vol. 57 (4) 2002
1. Centro de Veterinária e Zootecnia, Faculdade de Medicina Veterinária,
Rua Prof. Cid dos Santos, Polo Universitário do Alto da Ajuda, 1300-477 Lisboa,
Portugal
2. Department of Animal Science, Faculty of Agriculture - University of
the Free State, PO Box 339, Bloemfontein, Republic of South Africa
Abstract
Fifteen Boer goat bucks, 6 to 8 months old, average weight 28 kg, were allocated to two groups
of similar age and body weight, and fed ad libitum for a 30 day period. The underfed group (n=8),
received a diet consisting only of Themeda trianda hay (cut during the winter) from a natural pasture
(3,84 % crude protein-CP). The supplemented control group (n=7) received a diet consisting on 71%
Themeda trianda, 22 % maize, 5.5 % molasses and 1.5 % urea (8,1%CP). Blood was collected weekly,
and plasma concentrations of insulin, T3 and T4 were determined. Concentrations of Insulin were
significantly higher in the T group. Both groups had similar concentrations of plasma T3 and T4.
Introduction
Frequently the lack of feed supplementation during the dry season in extensive or traditional
animal production systems in the tropics and subtropics, leads to a seasonal weight loss of up to 40 %
[1]. This unavailability of feed and consequent undernutrition is a serious limitation to animal
production in several African countries, particularly South Africa [2].
Insulin is a hormone secreted by the ß cells of the Langerhans islets in the pancreas [3], and
plays a major role in the catabolism of glycogen, amino acids and fatty acids in situations of
undernutrition. Insulin plasma concentrations are proportional to nutrient intake, higher in ad
libitum fed animals than in those subjected to food restriction [4]. This was demonstrated by
Borrebaek et al. in observations on the insulin circadian rhythms of Norwegian red cattle [5]. In
short periods of undernutrition insulin concentration tends to diminish when compared to
normally fed lambs [6]. A similar situation can equally be observed in longer periods of
undernutrition as demonstrated in horses [7], cattle [8] and rats [9].
T3 and T4 are secreted by the thyroid and have a strong influence on the metabolism of
carbohydrates, proteins and lipids by favouring intestinal absorption of glucose and its deposition in
muscular and adipose tissue; increased essential amino acid absorption, reduced plasma cholesterol and
increased absorption of low density lipoproteins LDL [3]. In farm animals the concentrations of T3 and
T4 in undernourished animals are rather inconsistent. In new-born piglets, Kasser et al. [10] detected
decreased T3 and T4 concentrations as fasting progressed, whereas Campion et al. [11] detected only
differences in T3 concentrations of underfed swine when compared to control animals. Adult horses
showed reducing T3 and T4 concentrations as fasting progressed [12]. In lambs, Taveira registered
significative differences in T3 concentrations in animals with weight loss compared to controls [13].
The objective of this study is to increase the knowledge of some endocrinological parameters in
the goat, for which limited information is available. We aim specifically to identify differences in the
concentrations of insulin, T3 and T4 in the plasma of young Boer goat bucks under two levels of
nutrition: underfed and supplemented.
Materials and Methods
Fifteen Boer goat intact bucks, aged 6 to 8 months, were divided in two experimental groups.
Underfed group (SA; n = 8) fed Themeda trianda winter hay from a natural pasture in the Free State
province of South Africa. Control group (T; n = 7) was fed a diet of the same hay (71%) plus 22%
maize, 5,5% molasses and 1,5% urea (see composition in Table 1).
Blood samples were collected on days 2, 7, 14, 21 and 28 after the beginning of the experiment.
Blood was centrifuged at 2500 rpm in a Hettich Rotanta centrifuge. Serum was separated with a pipette
and stored in vials kept at -200 C.
Insulin concentrations were determined by radioimmuno assay (RIA), with Ciba - Corning Coat
- A - Count equipment and reagents. T3 and T4 analysis were performed with Chiron Diagnostics
equipment and reagents.
Data were compared by ANOVA repeated measures.
Table 1: Feed composition
Crude Protein
(g/kg)
Crude Energy
(kJ/100g)
Hay
Maize
Molasses
Urea
38.4
91.0
49.0
2857.0
1508
1583
1309
897
Results
Results are presented in Table 2. The supplemented group showed higher concentrations of
insulin than those observed in the underfed group on days 2, 14 and 28. No significant difference was
registered regarding T3 and T4 concentrations at the same collection dates.
Table 2: Insulin, T3 and T4 concentrations in the plasma of Boar goats.
Day 2
Day 7
Day 14
Day 21
Day 28
T*
SA**
T
SA
T
SA
T
SA
T
SA
Insulin
9.1b
4.5c
7.3bc
5.9c
11.8a
7.4bc
8.7b
7.9b
9.3b
6.9c
(µIU/ml)
(0.9)
(0.4)
(0.6)
(0.9)
(1.3)
(0.6)
(1.1)
(1.9)
(0.8)
(0.7)
T3
1.12bc
1.03bc
0.9bc
0.9c
1.4a
1.2ab
1.3ab
1.3b
1.14ab
1.19ab
(nmol/l)
(0.1)
(0.07)
(0.06)
(0.06)
(0.1)
(0.13)
(0.1)
(0.13)
(0.05)
(0.12)
T4
56.8b
58.5b
47.6b
46.1b
68.8ab
73.1a
54.2b
62.6ab
58.7b
56.9b
(nmol/l)
(4.43)
(5.92)
(3.8)
(2.6)
(5.3)
(5.7)
(4.3)
(3.3)
(4.1)
(5.5)
Results with different superscripts in the same row indicate statistical significance (p<0.05);
Standard Error of Mean values in parenthesis
* T = Control group
** SA = Underfed group
Discussion
As seen in Table 1, supplemented group animals had access to highly important sources of
nitrogen (urea) and carbohydrates (maize and molasses), whereas SA group animals had access to a
ration of very poor nutritional characteristics, rich lignin and extremely fibrous. Under these
conditions, animals fed the supplemented diet were able to increase their bodyweight during the
experimental period by approximately 10 % (data not shown). In such conditions, significative
differences were registered between insulin concentrations of the two experimental groups. The
underfed group showed concentrations of between 4.5 to 7.9 µIU, corresponding to approximately 65
to 75 % of those observed in supplemented animals (7 to 12 µIU). The marked differences between
the two diets explain the different insulin concentrations. Such differences have been described
by Brockman and Laarveld [4], Cole et al. [6], Glade et al. [7], Rule et al. [8] and Cardoso and
Stock [9]. The insulin concentrations obtained in our assay seem to indicate significant
differences between glucose levels in both groups, hence characterising the nutritional status of
both groups and indicating reduced protein synthesis and an increased catabolism [14].
It would be expected that, under situations of undernutrition, such as the described for group
SA, T3 and T4 concentrations would decrease as observed in wild deer under food shortage [15]. This
could be explained as an attempt by the organism to increase its lipid and protein catabolism. Inversely
in adequately fed animals such as those of group T, higher concentrations of T3 and T4 would be
expected to increase absorption of intestinal glucose, essential amino acid and lipoprotein.
Nevertheless, no significant differences were registered regarding T3 and T4 concentrations of both
experimental groups. In fact T3 concentrations for both groups ranged from 0.9 to 1.4 nmol / l, and T4
concentrations had values within the 45 to 75 nmol / l interval. These results are similar to those of
Kasser et al. [10] and Campion et al. [11] that describe extremely high inconsistencies between the
results of adequately fed and underfed animals. Our results therefore indicate that in the male Boer goat
breed and under the conditions of the experiment, undernutrition does not influence T3 and T4
concentrations which remain similar to adequately fed animals.
Aknowledgements
Authors would like to thank the Science and Technology Foundation of Portugal / Fundação
para a Ciência e a Tecnologia (PRAXIS XXI/BM/17921/98) for financial support. The kind cooperation of Miss D. duBrüyn, Mr. T. Muller and Mr. W. Combrink is acknowledged.
LINKS TO OTHER ARTICLES IN THIS ISSUE
References
1.
[1] Clariget, R.P., Forsberg M. and Rodriguez-Martinez H.: Seasonal variation in live weight,
testes size, Testosterone, LH secretion, Melatonin and Thyroxine in Merino and Corriedale rams in
SubTropical climate. Acta Vet. Scand. 39: 35-47, 1998.
[2] Lusweti, E.C.: The performance of the Nguni, Afrikander and Bonsmara cattle breeds in
developing areas of Southern Africa. South African J. Anim. Sci. 30 S1: 28-29, 2000.
[3] Cunnigham, J.G.: Endocrine glands and their function. In: Cunningham, J.G. (Editor):
Textbook of Veterinary Physiology. Saunders, London, pp. 655-699, 1992.
[4] Brockman, R.P. and Laarveld, B.: Hormonal regulation of metabolism in ruminants; a
review. Livestock Prod. Sci. 14: 313-334, 1986.
[5] Borrebaek, B., Halse, K., Tveit, B., Dahle, H.K. and Ceh, L.: Plasma glucose, ketone bodies,
Insulin, Glucagon and Enteroglucagon in cows: Diurnal variations related to ketone levels before
feeding and to the ketogenic effects of feeds. Acta Vet. Scand. 31: 5-15, 1990.
[6] Cole, N.A., Purdy, C.W. and Halford, D.M.: Influence of fasting and postfast diet energy
level on feed intake, feeding pattern and blood variables of lambs. J. Anim. Sci. 66: 798-805, 1988.
[7] Glade, M.J., Gupta, S. and Reimers, T.J.: Hormonal responses to high and low planes of
nutrition in weanling thoroubreds. J. Anim. Sci. 59: 658-665, 1984.
[8] Rule, D.C., Beitz, D.C., de Boer, G., Lyle, R.R., Trenkle, A.H. and Young, J.W.: Changes in
hormone and metabolite concentrations in plasma of steers during a prolonged fast. J. Anim. Sci. 61:
868-875, 1985.
[9] Cardoso, L.A. and Stock M.J.: Effect of clenbuterol on endocrine status and nitrogen and
energy balance in food-restrictd rats. J. Anim. Sci. 76: 1012-1018, 1998.
[10] Kasser, T.R., Martin, R.J., Gahagan, J.H. and Wangness, P.J.: Fasting plasma hormones
and metabolites in feral and domestic newborn pigs. J. Anim. Sci. 53: 421-426, 1981.
[11] Campion, D.R., McCusker, R.H., Buonomo, F.C. and Jones Jr., W.K.: Effect of fasting
neonatal piglets on blood hormone and metabolite profiles and on skeletal muscle metabolism. J. Anim.
Sci. 63: 1418-1427, 1986.
[12] Messer, N.T., Johnson, P.J., Refsal, K.R., Nachreiner, R.F., Ganjam, V.K. and Krause,
G.F.: Effect of food deprivation on baseline iodothyronine and cortisol concentrations in healthy adult
horses. Am. J. Vet. Res. 56: 116-121, 1995.
[13] Taveira, O.S.: Estudo da intervenção metabólica do clenbuterol em ovinos submetidos a
restrição alimentar (Study of the influence of clenbuterol in underfed sheep). MSc thesis, Faculty of
Veterinary Medicine, Lisbon, 1998
[14] Moldawer, L.L., Bistrian, B.R. and Blackburn, G.L.: Factors determining the preservation
of protein status during dietary protein deprivation. J. Nutr. 111: 1287-1296, 1981.
[15] Willard, S.T., Neuendorf, D.A. and Randel, R.D.: Voluntary feed intake, growth
characteristics and serum concentrations of thyroid hormones in males and females axis fawns (Axis
axis). Small Rum. Res. 30: 19-27, 1998.