Growth performance and hormonal status during feed restriction and compensatory growth of Small-Tail Han sheep in China

Abstract

Average daily gain (ADG), hormonal status and gain:feed intake ratio were determined in Small-Tail Han lambs (initially 24±1.8kg; 90±11days of age) during feed restriction and compensatory growth. An adaptation period of 14days was allowed during which time the sheep consumed feed (crude protein=148g/kg; metabolizable energy=15.9MJ/kg DM) ad libitum. This was followed by 30days of feed restriction in which three groups of lambs (n=10 per group) received approximately 85 (Tr1), 75 (Tr2) and 60% (Tr3) of ad libitum intake; a fourth group (control, CK; n=10) continued to receive ad libitum feed. After the restriction period, all lambs were fed with ad libitum intake for 60 days. During feed restriction, the control sheep had higher ADG than the other three groups (P<0.01). The gain:feed intake ratios of CK and Tr1 were higher than for Tr2 and Tr3 (P<0.01). But during re-alimentation, ADG of Tr2 and Tr3 were higher than control lambs (P<0.01) while final body weight (BW) was similar among groups. Gain:feed intake did not differ among the four groups. Following feed constriction, there was no difference in dry matter intake (DMI) among the four groups during the 60-days feed re-alimentation period. There was no difference in plasma concentrations of growth hormone, insulin and insulin-like growth factor 1, triiodothyronine, thyroxine or cortisol. Within restricted groups, GH generally decreased during the restricted feeding period and increased with ad libitum feed intake. In addition, plasma IGF-1 concentration of all experimental lambs generally increased in the latter stages of the ad libitum feed intake. These changes were most pronounced in the two most feed restricted groups. In conclusion, the lambs in the highest feed restriction group (60% of ad libitum intake) were able to compensate completely for the reduced BW. The total DMI over the whole period of the highest restricted feed intake group was 14.2% lower than the control group (P<0.05). Therefore, the strategy of restricted feed would be economical for fattening lambs in China.