Effects of Cotton Stalk and Sugar Beet Pulp Silage on Growth Performance, Serum Biochemistry, Rumen Fermentation, and Microbiota in Suffolk Ram Lambs

This study evaluated the effects of replacing whole-plant corn silage with cotton stalk and sugar beet pulp mixed silage at 0, 30, 60, or 90% on growth performance, serum parameters, and rumen characteristics in Suffolk ram lambs, addressing the lack of systematic research on moderate-to-high replacement ratios in sheep diets. Eighty-four 4-month-old ram lambs (32.36 ± 2.92 kg) were assigned to four treatments (3 pens/treatment, 7 lambs/pen) for a 120-day trial after a 15-day adaptation. Based on the growth performance and serum parameter results, the control and 60% replacement groups were selected for further analysis of rumen fermentation and bacterial microbiota via 16S rRNA gene sequencing. Compared with the control, the 60% replacement group showed increased final body weight (+15.7%, p < 0.01), daily weight gain (+38.4%, p < 0.01), and dry matter intake (+8.6%, p < 0.05), and improved feed-to-gain ratio (F:G) (p < 0.01). Serum immunoglobulin A and G increased (p < 0.05), whereas tumor necrosis factor-α and interleukin-1β decreased (p < 0.05) in the 60% and 90% replacement groups. Serum MDA was significantly lower in the 90% CSBPS group than in the control at d 90 (p < 0.05), with no significant differences among groups at d 120. Rumen isobutyric and valeric acid concentrations were greater in the 60% replacement group than in the control (p < 0.05), accompanied by enrichment of fiber-degrading bacteria including the Lachnospiraceae NK3A20 group. Replacing 60% of whole-plant corn silage with cotton stalk and sugar beet pulp silage was associated with improved growth performance, enhanced immune function and antioxidant status, and optimized rumen fermentation in Suffolk ram lambs under the conditions of this study.