Rumen fermentation and bacterial communities in weaned Chahaer lambs on diets with different protein levels

We evaluated the effects of diets with different crude protein (CP) levels on growth performance, rumen fermentation and bacterial communities in weaned Chahaer lambs. 128 weaned Chahaer lambs ((20.56±1.43) kg body weight; ram:ewe 1:1) aged (61±1.85) d were randomly allotted to one of four diets with CP content of 11.17% (T1), 12.06% (T2), 13.40% (T3) or 14.36% (T4). Ruminal fermentation parameters were measured and bacterial communities were analysed using PCR-dena-turing gradient gel electrophoresis (PCR-DGGE) and quantitative PCR. The average daily gain and feed utilization efficiency in T3 were higher than those in the other groups (P<0.05), although the dry matter intake and metabolizable energy intake were similar. Total volatile fatty acid concentration in the ruminal fluid of T3 was lower than that of T1 (P=0.011), T2 (P=0.008) or T4 (P=0.309). The ammonia nitrogen concentration and acetate/propionate ratio of ruminal fluid were significantly higher in lambs fed the higher CP diets, whereas the molar concentrations of propionate and butyrate of ruminal fluid were lower. The rumen bacterial community was similar in T2 and T3 which shown more stable and diverse rumen microbes ecosystem compared with the other groups. The DGGE profiles and phylogenetic tree indicated that Bacteroides uniformis, Clostridium alkalicellulosi, Alkalibaculum bacchi and Saccharofermentans sp. were common bacterium of Chahaer lamb rumen. B. uniformis, C. alkalicellulosi, Saccharofermentans sp. and Gracilibacter thermotolerans, which belong to the Bacteroidetes and Firmicutes phyla, were the dominant species in the rumen of lambs fed 13.40% CP. However, Ruminococcus albus, Ruminococcus flavefaciens and Butyrivibrio fibrisolvens were not different in lambs fed different CP diets. Therefore, it could be concluded that B. uniformis, C. alkalicellulosi, A. bacchi and Saccharofermentans sp. were common bacteria of Chahaer lamb rumen. Furthermore, the dietary CP of 13.04% could improve performance and change rumen fermentation model by increasing the dominant species' peak intensities of B. uniformis, C. alkalicellulosi, Saccharofermentans sp. and Gracilibacter thermotolerans and stabilizing rumen microbial ecosystem.