Abstract: The purpose of this experiment was to study the effect of adding Bacillus subtilis to milk replacer on the growth performance, tissues and organs development, diarrhea rate and fatty acids deposition in muscle in 7-28 days old Hu lambs. Thirty 7-day-old Hu male lambs (twins) with well-developed body conditions were selected and divided into 2 groups randomly according to the principle of homogeneity, 15 lambs in each group and each one as a repeat. Lambs in the two groups were fed milk replacer with a Bacillus subtilis content of 0 and 0.2%, respectively. The test lasted for 21 days. The lambs were weighed before morning feeding at 7, 14, 21 and 28 days of age, and then the average daily gain (ADG) of each growth stage was calculated. The feces conditions were observed during the whole feeding trial, and the lamb diarrhea rate was calculated. At the age of 28 days, 8 lambs in each group were randomly selected for slaughter. After slaughter, the weight of each tissue and organ was weighed, and the relative index was calculated. The longissimus dorsi and biceps brachii of lamb were collected to measure the intramuscular fat content. The results showed that:1) Bacillus subtilis significantly reduced the final weight of 7-14 days old lambs (P<0.05), significantly increased the ADG of 15-21 and 22-28 days old lambs (P<0.05). Bacillus subtilis increased the ADG of 7-28 days old lambs (P=0.100). Bacillus subtilis had no significnat impact on the diarrhea rate of lambs (P>0.05). 2) Bacillus subtilis significantly reduced the pancreas weight of 7-28 days old lambs (P<0.05), and significantly increased the proportion of hooves weight to live weight before slaughter (P<0.05). Bacillus subtilis had no significant effect on other tissues and organs of lambs (P> 0.05). 3) Bacillus subtilis had no significant effect on the skin and wool development of 7-28 days old lambs (P>0.05). 4) Bacillus subtilis significantly reduced the content of unsaturated fatty acid (UFA), monounsaturated fatty acid (MUFA), palmitic acid, stearic acid, eicosanoic acid, palmitoleic acid, oleic acid and MUFA:polyunsaturated fatty acid (PUFA)(P<0.05), and significantly increased saturated fatty acid (SFA):UFA and content of pentadecane acid, myristoleic acid and nervonic acid in longissimus dorsi of lambs (P<0.05). Bacillus subtilis significantly reduced the contents of UFA, SFA, MUFA, palmitic acid, stearic acid, eicosanic acid, palmitoleic acid, oleic acid and MUFA:PUFA(P<0.05), and significantly increased the content of PUFA, n-6PUFA, myristoleic acid, nervonic acid and SFA:UFA, PUFA:SFA in biceps brachii of lambs (P<0.05). Supplementing Bacillus subtilis to milk replacer did not affect the diarrhea rate, organs and skin development of 7-28 days old Hu lambs, however, the ADG and carcass weight of lambs tended to increase. Supplementing Bacillus subtilis significantly reduced the content of UFA, MUFA, and MUFA:PUFA in the longissimus dorsi and the content of UFA, SFA, MUFA, and MUFA:PUFA in the biceps brachii of Hu lambs, while significantly increased the SFA:UFA in the longissimus dorsi and the contents of PUFA, n-6PUFA, and SFA:UFA, PUFA:SFA in the biceps brachii of Hu lambs. The result shows that supplementating Bacillus subtilis can improve the meat quality of Hu lambs by regulating the composition and content of intramuscular fatty acids.

Key words: milk replacer, Bacillus subtilis, growth, organs, fatty acids