Comparison of Ruminal Protected Versus Non-Protected Live Yeast on Omasal Flows, Site and Extent of Digestion in the Digestive Tract of Beef Heifers Fed High-Grain Diet

The objective of this study was to determine the effect of adding ruminal protected versus non-protected live yeast (LY) on DM intake, omasal flows, site and extent of feed digestion in the digestive tract of beef heifers. The LY was encapsulated using barley protein (mainly hordein and glutelin) extracted from barley grain. Five rumen cannulated beef heifers (BW = 650 ± 48.8 kg) were used in a 5 × 5 Latin square design. Heifers were fed ad libitum total mixed diet containing 10% barley silage and 90% barley-based concentrate (DM basis). Five treatments were: 1) control (no additives); 2) antibiotics (28 mg monensin + 11 mg tylosin/kg dietary DM); 3) 1.5 g LY/d; 4) 3.5 g encapsulated LY/d (ELY); and 5) combination of treatments #3 and 4 (MLY). The encapsulated LY consisted of 1.5 g LY and 2 g capsule. Number of yeast colonies was 1.71 × 10¹⁰ cfu/g. Digesta and rumen microbes were labeled with Yb and ¹⁵N, respectively. Data were analysed using the MIXED procedure of SAS with model including fixed effect of treatment and random effects of heifer and period. Intake of DM (averaged 11.8 kg/d) was not affected by treatment. No treatment effects on flows (kg/d) of OM (5.4) and starch (0.75) to the omasum were observed, whereas flows of NDF were greater (P < 0.02) with antibiotics (1.9) than ELY (1.7). Ruminal digestibility of OM tended (P ˂ 0.09) to be less with ELY (62.4%) or MLY (62.9) than control (66.4%) or antibiotics (68.1%), but no differences in ruminal digestibility of NDF (averaged 44.1%) and starch (averaged 83.0%) were observed among treatments. In contrast, greater (P ˂ 0.03) postruminal digestibility (% of intake) of OM (30.9 vs. 22.9%) and NDF (17.9 vs. 7.9%) was observed with ELY and MLY than control and antibiotic groups. As a result, digestibility of OM (81.1 vs. 77.0%) and NDF (64.1 vs. 49.9%) in the total digestive tract was greater (P ˂ 0.01) with ELY or MLY than control. No treatment effect was observed on the flows of N to omasum (averaged 292 g/d) and microbial protein synthesis (averaged 147 g/d). Digestibility of N in the total digestive tract was greater (P ˂ 0.02) with ELY or MLY than control (79.2 vs. 75.4%). These results indicate the potential postruminal activity of LY, and benefits to feeding protected LY on improving intestinal digestibility of nutrients in beef heifers fed high-grain diet.