Rumen microbes play an important role in the growth and development of ruminants. Differences in variety will affect the rumen community structure. The three excellent sheep breeds were selected for this study (Hu sheep, Tan sheep, and Dorper sheep) have different uses and origins. The sheep were raised on the same diet to 180 days of age in a consistent environment. 16S rDNA V3-V4 region sequencing was used to assess the rumen microbes of 180 individuals (60 per breed). There were differences in microbial diversity among different sheep breeds (p < 0.05). Principal coordinate analysis showed that the three varieties were separated, but also partially overlapped. Linear discriminant analysis effect size identified a total of 19 biomarkers in three breeds. Of these biomarkers, five in Hu sheep were significantly negatively correlated with average feed conversion rate (p < 0.05). Six biomarkers were identified in the rumen of Dorper sheep, among which Ruminococcus was significantly positively correlated with body weight at 80 days (p < 0.05). In Tan sheep, Rikenellaceae_RC9_gut_group was significantly positively correlated with meat fat, and significantly positively correlated with volatile fatty acids, such as butyric acid and isobutyric acid (p < 0.05). The Rikenellaceae_RC9_gut_group may regulate Tan mutton fat deposition by affecting the concentration of volatile fatty acids. Functional prediction revealed enrichment differences of functional pathways among different sheep breeds were small. All were enriched in functions, such as fermentation and chemoheterotrophy. The results show that there are differences in the rumen microorganisms of the different sheep breeds, and that the microorganisms influence the host.

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Feeding with a suitable level of milk replacer (MR) can improve the survival rate and stimulate the growth potential of early lambs. However, feeding excessive MR might be detrimental to rumen development and microbial colonization. Herein, we investigated the effects of feeding different levels of MR on rumen digestive function and ruminal microorganisms. Fourteen healthy male Hu lambs with similar birth weights and detailed pedigree records were divided into two groups to receive low (2% of average body weight per day) and high (4% of average body weight per day) levels of MR. We analyzed the effects of the MR feeding level on growth performance, fiber degradation rates, rumen fermentation parameters, enzyme activities and rumen histomorphology. We found that feeding with a high level of MR improved the average daily gain of early lambs, but decreased the starter intake, rumen weight and papillae length. We also analyzed the effects of the MR feeding level on the rumen microbiota using 16S-rRNA amplicon sequencing data. The results showed that high a MR feeding level increased the rumen microbial diversity but decreased the abundance of many carbohydrate degrading bacteria. Several bacterial genera with significant differences correlated positively with rumen cellulase activity and the acid detergent fiber degradation rate. Our results suggested that a high level of MR could improve the growth performance of early lambs in the short term; however, in the long term, it would be detrimental to rumen development and have adverse effects on the adaptation process of the microbiota to solid feed.

Early mammal gut microorganism colonization affects host health, the feed conversion rate, and production performance. Herein, we explored how fecal microbiota develops and the interactions between microorganisms and nutrients. The lambs were separated from ewes at 7 days old, artificial feeding with milk replacer completely replaced lactation, and the starter diet was added. At 21 days old, the lambs were fed with complete starter and milk replacer was stopped. At day 7, 21, 35, and 49 after birth, fecal samples were collected. Then 16S rRNA gene sequencing in the fecal samples revealed that the alpha diversity increased significantly with age. Principal coordinates analysis showed clear clustering by age (p < 0.05). At the genus level, the relative abundance of 8 genera declined, 12 genera increased (p < 0.1), and 4 genera changed dramatically with age (p < 0.05). The apparent digestibility of dry matter, protein, fat, neutral detergent fiber, and acid detergent fiber significantly decreased by 21.77%, 23.15%, 23.62%, 19.38%, and 45.24%, respectively, from 7 to 35 days of age (p < 0.05), but not thereafter (p > 0.05). Fecal nutrient contents affected the abundance of bacterial genera (p < 0.05). Enterobacteriaceae_unclassified, Clostridium XlVb, Bifidobacterium, and other genera had no relationship with the fecal nutrient content; however, they were closely related to nutrient intake and digestibility, possibly promoting nutrient digestion. Our results suggested that nutrient digestion of young lambs changed rapidly, which was closely related to intestinal microbial colonization.

Fat deposition is an important economic trait that is closely related to feed efficiency and carcass performance in livestock. In this study, the fat deposition-related traits of 1,293 Hu sheep were measured and descriptive statistical analysis was conducted. The results showed that the coefficient of variation of all fat deposition-related traits was higher than 24%. In addition, single nucleotide polymorphisms and the expression characteristics of TRAPPC9 (encoding trafficking protein particle complex subunit 9) and BAIAP2 (encoding brain-specific Angiogenesis inhibitor 1-associated protein 2) genes in Hu sheep were detected using PCR amplification, Sanger sequencing, KASPar genotyping, and quantitative real-time reverse transcription PCR (qRT-PCR). The associations between SNPs and fat deposition-related traits were also analyzed. Two intronic mutations, TRAPPC9 g.57654 A &gt; G and BAIAP2 g.46061 C &gt; T, were identified in Hu sheep. The result of association analysis showed that TRAPPC9 g.57654 A &gt; G and BAIAP2 g.46061 C &gt; T were both significantly associated with the weight of tail fat, tail fat relative weight (body weight), and tail fat relative weight (carcass) (P &lt; 0.05). Comprehensive effects analysis showed that there were significant differences between the combined genotypes and tail fat and perirenal fat deposition. Moreover, qRT-PCR analysis showed that TRAPPC9 and BAIAP2 are widely expressed, and their expression levels were significantly higher in the small-tail group compared with those in the big-tail group (P &lt; 0.01). These results provided important candidate molecular markers that could be used in strategies to reduce tail fat deposition in Hu sheep.