Abstract:
Animal Production in Australia 1998 Vol. 22 EFFECT OF SEASON AND NUTRITION ON PLASMA GROWTH HORMONE (GH) AND INSULIN-LIKE GROWTH FACTOR-1 (IGF-1) CONCENTRATIONS IN GOAT BUCKS. S. W. WALKDEN-BROWNAB G.D. RAMANAHB, ZHU HAIB and G.B. MARTIN A B B Division of Animal Science, University of New England, Armidale, NSW 2351 Faculty of Agriculture, University of Western Australia, Nedlands, WA 6907 Australian feral goat bucks show seasonal cycles in testicular size and body weight that are closely associated, and testicular size is very responsive to nutritionally-induced changes in body weight (WalkdenBrown et al. 1994). The hormones of the somatotrophic axis might be involved in these effects so, as part of a study into the effects of season and nutrition on growth and reproductive function in feral goat bucks, we examined plasma concentrations of GH and IGF-1. Between September 1994 and April 1995, two experiments were conducted using mature feral bucks. In Experiment 1 five bucks were placed on a unchanging maintenance diet for the duration of this period. In Experiment 2, bucks were placed on half maintenance (0.5M), maintenance (M) or twice maintenance (2M) diets (n=6/diet) for periods of 42 days commencing on 2 September 1994 (Spring, non-breeding season), 7 December 1994 (Summer, transitional period) and 14 March 1995 (Autumn, breeding season). Bucks in both Experiments were fed a basal diet of 200 g oaten chaff with the balance of the ration made up of a high quality pelleted ration. On Days -1, 11 and 42 of each experimental feeding period blood samples were collected at 20 minute intervals over 24 hours. Pooled plasma samples for each buck were assayed for GH and IGF-1 by RIA. Data were analysed by ANOVA. Results are shown in Table 1 and Figure 1. Table 1. Mean (� s.e.) growth hormone and IGF-1 concentrations in Experiment 1. Date (season) Sept. 1 (Win/Spring) Dec. 6 (Summer) Mar. 13 (Autumn) ab Reproductive season Non-breeding Transitional Breeding Plasma GH (ng/ml) 2 3 . 4�6.7 b 7.5�1.1 b 4.4�1.8 a Plasma IGF-1 (ng/ml) 141�18 231�35 140�21 a b a Means not sharing the same superscript are significantly different P<0.05 Figure 1. Experiment 2. Mean (� s.e.) change in growth hormone and IGF-1 concentrations in response to 0.5M ( ), M ( ) and 2M ( ) diets at different times of the year (n=6/diet). Significant differences within a time period (P<0.05) a: 0.5M vs 2M; b: 0.5M v M; c: M vs 2M. These results are the first demonstration that both GH and IGF-1 concentrations show distinct seasonal variation in the goat, and that, as with other ruminants, GH concentrations are depressed and IGF-1 concentrations increased, with improving nutrition. WALKDEN-BROWN, S.W., RESTALL, B.J., NORTON, B.W., SCARAMUZZI, R.J. and MARTIN, G.B. (1994). J. Reprod. Fert. 102, 351-360. 412
