Fat-tailed and thin-tailed lambs responses to glucose and insulin challenges during different energy balances

The proportion of adipose depots varies considerably between fat-tailed (FT) and thin-tailed (TT) sheep breeds. FT breeds accumulate majority of body fat in fat-tail depot, whereas TT breeds deposit considerable proportion of body fat in visceral depots. These differences in proportion of adipose depots seem to affect body metabolism due to differences in metabolism of different depots. Hence, the current research aimed to evaluate the response of fat-tailed lambs (FTL) and thin-tailed lambs (TTL) to glucose and insulin challenges during negative energy balance (NEB) and positive energy balance (PEB). Glucose tolerance and insulin challenge tests were conducted on randomly selected lambs from each genotypes at the end of induced NEB and PEB. Glucose injection during NEB caused greater plasma glucose concentration in TTL, whereas in PEB, the enhancement in glucose concentration as a consequence of glucose injection was higher in FTL (P≤0.09). The area under the glucose curve was higher in FT compared to TT lambs during glucose tolerance test regardless of energy balance (EB; P≤0.03). The clearance rates of insulin (P≤0.09) and glucose (P≤0.006) in the respective insulin and glucose tolerance tests were higher during PEB compared to NEB regardless of the genotypes. These results demonstrated that induced NEB can enhance insulin resistance in both FT and TT lambs, severity of which is greater in FT than in TT lambs.