Effects of adding live Saccharomyces cerevisiae and Aspergillus-based enzyme extracts on ruminal fermentation, plasma polyamine concentrations, and fiber digestibility in beef steers fed a high-forage diet

Abstract

We evaluated the effects of adding live Saccharomyces cerevisiae (SC) and Aspergillus -based extract (ABE) on rumen fermentation, plasma polyamine concentrations, and in vitro fiber digestibility in beef steers fed mixed red clover–orchardgrass hay. Eight rumen-cannulated Angus crossbred beef steers were assigned to 4 treatments arranged in a replicated 4 × 4 Latin square design with four 21-d periods. Dietary treatments were (1) control (CON; basal diet without additive), (2) SC (CON + 15 g/d of live SC), (3) ABE (5 g of ABE), and (4) SC+ABE (15 g/d of live SC + 5 g of ABE). On d 21, blood samples were collected before morning feeding for plasma metabolome analysis (including polyamines such as spermines, spermidine, and putrescine). Rumen fluid samples were collected 3, 6, and 9 h after feeding for analysis of VFA, ammonia-N concentrations, and in vitro DM and NDF digestibility. Compared with CON, neither SC nor ABE had effects ( P > 0.10) on rumen fermentation and in vitro digestibility. In contrast, SC+ABE increased ( P ≤ 0.05) the ruminal concentrations of acetate, butyrate, and total VFA and in vitro DM and NDF digestibilities. Both SC and SC+ABE increased ( P < 0.05) plasma concentrations of spermidine, spermine, and kynurenine. Supplementation of SC with or without ABE to forage-fed beef steers increased plasma concentrations of polyamines and kynurenine, a possible indication of improved immune function; however, combining SC and ABE, but not SC alone, improved the rumen fermentation and in vitro fiber digestibility.