Abstract: This study aimed to evaluate the variation in rumen fermentation and microbiota of pre- and post- early weaning lambs so as to provide theoretical basis for understanding the rumen development and early breeding of lambs.Sixteen male lambs with similar birth weight (BW,3.81 kg±0.55 kg) were selected.Lambs were fed breast milk from 1 to 7 days old.The lambs were separated from their dams at 8 days old and began to be fed milk replacer (MR) (at 2% of BW measured on day 8,three equal amounts) and starter feeds (ad libitum).MR feeding was stopped at 35 days of age.Six lambs were slaughtered pre-weaning (21 days old) and post-weaning (42 days old) respectively and rumen contents were collected to determine rumen fermentation,enzyme activity and microbiota.The results showed that the total volatile fatty acids,acetic acid,propionic acid,butyric acid,activities of cellulase and α-amylase for post-weaning lambs were higher than those for pre-weaning lambs (P<0.01).The diversities and abundances of rumen flora for post-weaning lambs were lower than those for pre-weaning lambs (P<0.05).The dominant phylum for pre- and post-weaning lambs were Bacteroidetes and Firmicutes,in which Bacteroidetes was the first phylum,accounting for 61.96% and 65.36% in pre- and post-weaning periods respectively.And Firmicutes was the second phylum,accounting for 32.08% and 24.03% in pre- and post-weaning periods respectively.The total of the two phylum accounted for 94.04% and 89.39% for pre-weaning and post-weaning lambs.The dominant genus for pre- and post-weaning lambs were unidentified_Prevotellaceae,accounting for 21.85% and 38.49% respectively.There was no significant change in rumen microbial function for pre- and post-weaning lambs,which all mainly focused on replication and repair,carbohydrate metabolism and translation.These results indicated that the rumen fermentation and enzyme activity were increased for post-weaning lambs,whereas the diversity and abundances of flora were decreased,the dominant flora and the function were similar between pre- and post-weaning lambs.

Key words: lamb; early weaning; rumen fermentation; microbiota