Effects of Arginine Supplementation on Growth Performance, Serum Parameters, and Rumen Microbial Diversity in Fattening Altay Sheep Fed a Forage-Based Diet

This study was conducted to investigate the effects of dietary supplementation with rumen-protected arginine (RP-Arg) on growth performance, rumen fermentation parameters, microbial diversity, and blood physiological and biochemical indices in fattening Altay sheep. A total of 24 healthy, 6-month-old Altay male lambs were randomly assigned to three groups, with eight replicates per group. The control group received a basal diet, while the experimental groups were supplemented with either 0.50% or 1.00% RP-Arg on a dry matter basis, respectively. The results indicated that RP-Arg supplementation had no significant effect on feed intake, growth performance, or slaughter performance of the lambs (p > 0.05), whereas backfat thickness decreased linearly (p < 0.05). With increasing RP-Arg levels, serum low-density lipoprotein cholesterol, leptin, and catalase activity increased linearly (p < 0.05), while blood ammonia, alanine aminotransferase, and Ig M exhibited a significant quadratic increase (p < 0.05). RP-Arg supplementation led to a linear decrease in ruminal propionate and valerate concentrations (p < 0.05). Analysis of bacterial diversity revealed that the class Vampirivibrionia and the order Gastranaerophilales were biomarkers for the 0.50% RP-Arg group, while several taxa within the phyla Proteobacteria and Thermoplasmatota served as biomarkers for the 1.00% RP-Arg group. In summary, although supplementation of a forage-based diet with RP-Arg partially modified rumen microbial composition and fermentation profile, and regulated several blood biochemical parameters, it did not translate into any beneficial effects on growth performance. Larger-scale studies are therefore warranted to further elucidate the role of RP-Arg in fattening lambs.