Insulin : regulation of growth potential?

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 18 INSULIN - REGULATION OF GROWTH POTENTIAL? P.A. SPECK*, V.H. ODDY** and P.C. WYNN* One of the major challenges in animal science is to identify physiological parameters that correlate highly with mature live weight at an early age. The use of these parameters as selection criteria is likely to increase the accuracy of modern breeding technology such as BLIP and thus increase the efficiency of genetic improvement in livestock industries. At Trangie, N.S.W., Merino flocks have been selected for 10 generations for (W+) and against (W-) weaning weight and as a result differ in mature live weight by 30%. The aim of the present study was to identify differences in metabolic hormone status between the two genotypes at different ages with a view to establishing endocrine criteria for possible use as selection markers for growth. Groups of W+ and W- wethers (n=lO) were weaned at 16 weeks and offered a At 6 months of age each 1ucerne:oats (60:40) pelletted ration ad libitum. group was split into 5 groups of 2, which were offered calculated energy intakes of either 0.4, 0.8, 1.2, 1.6 or 2.0 times maintenance of the same ration. After a 10 day equilibration period, serial blood samples were collected at 20 min. intervals for 5 h via jugular catheters. The animals were reallocated to another dietary energy level and the protocol repeated 10 days later. All animals were returned to ad libitum intakes and the same procedure repeated at 12 months of age. Plasma hormone levels were measured by RIA. Plasma IGFl and GH levels did not differ with change in energy intake in either genotype at either age, but there were significant differences between Plasma insulin levels also differed genotypes in mean plasma IGFl levels. significantly (P~0.05) between genotypes at both ages. In addition a significant interaction (P<O.Ol) existed between plasma insulin and intake in The slope of the relationship between each genotype by age treatment group. insulin and level of intake differed significantly (P<O.OS) between genotypes at 12 months but not at 6 months of age. Table 1 Live weight and hormone concentrations Speck et al. (1989) showed a positive relationship between protein gain and insulin but not IGFl in W+ but not W- sheep. The results suggest that insulin plays an important role in the regulation of the growth process and thus appears to be a useful metabolic hormone for the identification of genetically superior lambs. The role of IGFl warrants further investigation. SPECK, P.A., ODDY, V.H. and WYNN, PC. (1989). Proc. Nutr. Soc. Aust. 14i108. * ** CSIRO, Division of Animal Production, Prospect, N.S.W. 2149. Elizabeth Macarthur Agricultural Institute, Glenfield, N.S.W. 2167. 552