Effects of different dietary nitrogen to sulfur ratios on the jejunum tissue morphology and microflora of Tibetan lamb

The intestinal tract of animals is an important digestive and absorbing organ. To investigate the effects of different nitrogen to sulfur ratios on jejunal morphology, microbial diversity, and function in Tibetan lambs, 150 Tibetan lambs aged 60 days old with similar initial conditions were randomly divided into 5 equal groups. Lambs were fed until 180 days of age on diets containing similar energy, with nitrogen to sulfur mass ratios of 10.5 ꞉ 1 (group A), 9 ꞉ 1 (group B), 7.5 ꞉ 1 (group C), 6 ꞉ 1 (group D), and 4.5 ꞉ 1 (group E). At the end of the experiment, 6 animals from each group were randomly slaughtered and then examined. The jejunum tissues and contents were collected to analyze the effects of dietary nitrogen to sulfur ratios on jejunum tissue morphology, microbial community structure, and function. The following results were noted: 1) The length and width of jejunum villi in groups B and E were significantly higher than the other three groups (P < 0.05), and the lengths of villi in groups A and D were significantly higher than that in group C (P < 0.05). The depth of crypts in group D was significantly higher in the other four groups (P < 0.05). The villus-length/crypt-depth quotient in groups B and E was significantly higher than in groups A, C, and D (P < 0.05). The mucosal layer thicknesses in groups B and E were significantly higher than in groups C and D (P < 0.05). The muscle-layer thickness in group B was significantly higher than those of other groups (P < 0.05). 2) The OTU and Chao1 indexes of the B and E groups were significantly higher than those of the A and C groups (P < 0.05). The Shannon indexes of the B and E groups was significantly higher than those of other groups (P < 0.05). The Simpson indexes of the C and D groups were significantly higher than those of groups B and E (P < 0.05). B, D, and E group Ace indexes were significantly higher than those of A and C groups (P < 0.05). 3) Analysis of community structure of the jejunal microbial flora at phylum and genus levels revealed that at the phylum level, the Firmicutes, Actinobacteria, Bacteroidetes, and Proteobacteria predominate. Among them, the abundance of Firmicutes in group B was significantly higher than in group C (P < 0.05). The abundances of Actinobacteria in groups A and C were significantly higher than in groups B and E (P < 0.05). In groups B and E, the abundance of Bacteroidetes was significantly higher than in A and C groups (P < 0.05), and the abundance of Proteobacteria in group E was significantly higher than in groups B and D (P < 0.05). At the genus level, the four dominant bacterial genera were Rhodococcus, Brevibacterium, Christensenellaceae-R-7-group, Quinella, and Rikenellaceae-RC9-gut-group. The abundances of Rhodococcus in groups A, C, and D were significantly higher than in groups B and E (P < 0.05); the Christensenellaceae-R-7-group in group B was significantly higher than in all other groups (P < 0.05), and Quinella in groups A and B was significantly higher than in groups D and E (P < 0.05). 4) The PICRUSt function prediction results for the 16S rRNA genome show that the functions of the jejunal microbial flora mainly involve transcription and the transport and metabolism of carbohydrates and amino acids, indicating that Tibetan lamb jejunum bacteria can improve the host’s carbohydrate and protein metabolism and absorption. In summary, the nitrogen to sulfur ratio at B and D levels is beneficial to the development of jejunum tissue morphology in Tibetan lambs and increases the diversity and richness of the jejunum microbial flora. From an economic perspective, a nitrogen to sulfur ratio of 9 ꞉ 1 is most conducive to efficient raising of Tibetan lambs.