Effects of Feeding a Mixed Silage of Cotton Stalks and Grape Pomace on Growth Performance, Serum Biochemical Parameters, and Jejunum Content Metabolism in Suffolk Rams

The use of agricultural by-products as feed is essential for sustainable animal husbandry. This study assessed the effects of substituting whole-plant corn silage with a mixed silage of cotton stalks and grape pomace on growth, serum biochemistry, and jejunal metabolomics in Suffolk rams. In this experiment, 135 rams (6-mo, 30.55 kg BW) were allocated to 0%, 50%, or 100% replacement (CG, EG50, EG100) and fed for 120 d after a 15-d adaptation. Compared with the CG, average daily gain improved by 27.3% and 17.5%, and feed conversion improved by 30.8% and 15.4% in EG50 and EG100 (p < 0.01). Compared with CG, the levels of BUN, TNF-α and IL-1β in serum of EG50 and EG100 were significantly decreased. The levels of IgG, IgM, IL-4, antioxidant enzymes and total antioxidant capacity were significantly increased (p < 0.05). Subsequently, the slaughter performance and jejunal content metabolome of CG and EG50 were further detected and analyzed. The results indicated that the live weight, eye area and muscle crude protein content of EG50 were extremely significantly higher than those of CG (p < 0.01). In jejunal contents, 31 differential metabolites (EG50 vs. CG) were enriched in ABC transporters, branched-chain amino acid biosynthesis, mineral absorption, purine and biotin metabolism, and glucagon signaling. In conclusion, substituting corn silage with the mixed silage promotes growth, improves antioxidant and immune status, reduces serum urea nitrogen, enhances muscle protein deposition (EG50), modulates intestinal nitrogen, purine, lipid, and carbohydrate metabolism (EG50), and supports sustainable meat sheep production.