Gengzhi Ding¹, Ying Chang¹, Zhenming Zhou¹, Liping Ren¹, Qingxiang Meng^1,

The objective of current study was to evaluate effect of Saccharomyces cerevisiae (SC) on rumen fermentation characteristics and fiber degradation in steers fed diets with different concentrate levels. Ten Simental × Local breed steers fitted with rumen fistulas were assigned to control and treatment groups. Steers were fed the same basal diets but the treatment groups received SC supplementation (8×10⁹ cfu/h/d) following a 2-period crossover design. Each period was comprised of four phases. From the 1^st to the 4^th phase, steers were fed in a stepwise fashion with incremental levels of concentrate diets at concentrate to forage ratios (CTFR) of 30:70, 50:50, 70:30 and 90:10, respectively. MIXED procedure was used to analysis effect of SC supplementation on parameters. Linear and quadratic responses for dietary CTFR were assessed using orthogonal polynomial contrast statements. The results showed that with dietary CTFR increasing, rumen pH, acetate and isobutyrate molar proportion, acetate: propionate, degradation rate (c_DM, c_NDF) and effective degradability (ED_DM, ED_NDF) of CRH linearly decreased (L; P < 0.01); TVFA concentration, molar proportion of propionate, butyrate, valerate and isovalerate and enzyme fibrotic activities linearly increased (L; P < 0.01), but concentration of rumen ammonia N, d+l-lactate and rapidly degradable fraction (a_DM, a_NDF) of CRH presented quadratic variation (Q; P < 0.01). Regardless of dietary CTFR, rumen pH, c_DM, c_NDF, ED_DM, ED_NDF of CRH and enzyme fibrotic activities with SC supplementation was higher compared to control groups (P < 0.05). Overall, SC possesses the capacity to stabilize rumen pH and to enhance fiber degradation.

fibrolytic activity, in situ, rumen fermentation characteristics, Saccharomyces cerevisiae, steer