The Chinese Tan sheep is a unique breed of sheep that is typical throughout China, mainly used for fur and meat production. They are widely distributed in northwestern China and are famous for their lambskin and shiny white curly wool. In this study, the phenotypic traits of wool length, birth weight, and head coat color were evaluated in 256 Chinese Tan sheep breeds. Whole genome sequencing generated 23.67 million high-quality SNPs for genome-wide association studies (GWAS). We identified 208 significant SNPs associated with birth wool length, implicating RAD50, MACROD2, SAMD5, SASH1, and SPTLC3 as potential candidate genes for this trait. For birth weight, 1056 significant SNPs, with 76.89% of them located on chromosome 2, were identified by GWAS, and XPA, INVS, LOC121818504, GABBR2, LOC101114941, and LOC106990096 were identified as potential candidate genes for birth weight. The GWAS for head coat color identified 1424 significant SNPs across three chromosomes, with 99.65% on chromosome 14, and SPIRE2, TCF25, and MC1R as candidate genes were found to be possibly involved in the development of the black-headed coat color in sheep. Furthermore, we selected head coat color as a representative trait and performed an independent test of our GWAS findings through multiplex PCR SNP genotyping. The findings validated five mutation sites in chromosome 14 (14,251,947 T>A, 14,252,090 G>A, 14,252,158 C>T, 14,252,329 T>G, and 14,252,464 C>T) within the exon1 of the MC1R gene (517 bp), as identified by GWAS in an additional 102 Tan sheep individuals, and revealed that black-headed sheep predominantly exhibited heterozygous genotypes, possibly contributing to their color change. Our results provide a valuable foundation for further study of these three economically important traits, and enhance our understanding of genetic structure and variation in Chinese Tan sheep.

Wolfberry (Lycium barbarum) sprouts are harvested on a large scale in Ningxia, and the residual tender stems and leaves constitute an abundant but largely unused by-product. This experiment was conducted to investigate the effects of dietary supplementation with different proportions of wolfberry (Lycium barbarum) sprout stems and leaves (WSSLs) on rumen fermentation and the rumen bacterial community of fattening Tan sheep, and to reveal the relationships between rumen bacteria and fermentation and growth traits. Forty-eight healthy 3-month-old weaned Tan rams with similar body weight ((22.75 ± 0.52) kg) were randomly divided into four groups of 12 sheep; the control group (G0) was fed a basal diet, while the G4, G8 and G12 groups were fed basal diets in which 4%, 8% and 12% of the corn straw was replaced by WSSLs. The adaptation period lasted 10 days and the experimental period 60 days. At the end of the experiment, six sheep per group (24 in total) were slaughtered and rumen contents were collected for fermentation measurements, and the V3–V4 region of the bacterial 16S rRNA gene was sequenced on the Illumina NovaSeq platform. Ruminal pH, ammonia nitrogen (NH3-N) and microbial crude protein (MCP) did not differ among groups (p > 0.05), whereas total volatile fatty acid (VFA) concentration differed (30.15–56.27 mmol/L; p = 0.025), together with acetate (p = 0.032) and butyrate (p = 0.010); these VFA differences were driven mainly by the high and variable values in the control group and showed no dose–response. Average daily gain was higher in G8 than in G0 and G4 (p = 0.010), and live weight before slaughter and carcass weight increased with the dietary WSSL level (p = 0.011 and 0.013). Seventeen phyla and 210 genera were identified, with Bacteroidota and Bacillota dominant; the relative abundance of Bacteroidota decreased while that of Bacillota tended to increase with the WSSL level, and Xylanibacter was the most abundant genus (15.85–18.18%). Alpha diversity indices did not differ among groups (p > 0.05), and principal coordinate analysis (PCoA) based on Bray–Curtis distance showed limited separation (Adonis R² = 0.157, p = 0.002). Nine genera showed nominal between-group variation (uncorrected p < 0.05); however, after Benjamini–Hochberg FDR correction across all 210 genera tested, none remained significant (all q = 1.00). Howardella was negatively correlated with acetate, propionate, butyrate and total VFA (p < 0.05), U29-B03 was positively correlated with live weight before slaughter and carcass weight (p < 0.05), and bacteria of Christensenellaceae were positively correlated with propionate, butyrate and total VFA (p < 0.05); none of these associations survived FDR correction. Dietary supplementation with 4–12% WSSLs did not depress growth performance and did not significantly alter the abundance of any individual taxon after correction for multiple testing; it moderately alters rumen bacterial community composition, and WSSLs can be used safely at inclusion levels of 4–12% as an unconventional feed resource for fattening Tan sheep.