Although several studies have implicated cortisol in the control of body composition in sheep, the precise mechanisms are unclear. Cortisol basal concentration and response to an ACTH challenge was studied in Coopworth wethers selected for (Fat) or against (Lean) fatness in both the fed and 48 hour fasted states at two stages (15 and 33 weeks). The aim was to investigate whether fasting, age or genotype would influence cortisol secretory parameters. Mean basal cortisol concentration was higher for fasted than fed lambs (13.6 versus 8.9 ng/ml, p<0.001), but did not differ significantly with genotype or overall stage of development. Maximal cortisol response to ACTH was greater for the fat than the lean genotype, at both 15 weeks (86.3 versus 65.3 ng/ml, p<0.01) and 33 weeks (108.2 versus 91.1 ng/ml, p<0.01) of age. Maximal cortisol response was also significantly greater with fasting and increasing age, but the effect of fasting on cortisol increase was greater at 15 than 33 weeks of age. Clearance of cortisol was significantly slower after fasting, but unaffected (p>0.05) by genotype and development. Basal cortisol concentrations was not associated with differences in body composition between the fat and lean genotypes. However the larger maximal response in the fat genotype may indicate that the adrenal gland plays a role in determining body composition.

DB, Binnie, JN Clarke, JB Clayton, CM Mowat, and RW Purchas

Proceedings of the New Zealand Society of Animal Production, Volume 55, , 104-107, 1995
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