Comparison of non-encapsulated and encapsulated active dried yeast on ruminal pH and fermentation, and site and extent of feed digestion in beef heifers fed high-grain diets.

The objective of this study was to determine whether feeding ruminally protected active dried yeast (ADY) exhibits postruminal activity in comparison with feeding non-protected ADY assessed by measuring feed intake, ruminal pH and fermentation, and site and extent of feed digestion in finishing heifers. A combination antibiotic was used as a positive control. Five Angus beef heifers with ruminal cannulas (body weight of 650 ± 48.8 kg) were used in a 5 × 5 Latin square design with 21-d periods and 1 week of washout between each period. The five treatments were: 1) control (no ADY and no antibiotics), 2) antibiotics (ANT; 300 mg monensin + 110 mg tylosin/d), 3) ADY (1.5 g ADY/d), 4) encapsulated ADY (EDY; 3.5 g/d containing 1.5 g ADY and 2 g capsule), and 5) mixture of ADY and EDY (MDY; 1.5 g ADY + 3.5 g EDY/d). The ADY was encapsulated using barley hordein and glutelin extracted from barley grain. The stability of encapsulated yeast in the rumen and its release in the intestine were validated in vitro. Intake (kg/d) of dry matter (DM) was not affected by treatments. Ruminal pH, total volatile fatty acid (VFA) concentration, and NH 3 -N concentration did not differ among treatments, whereas molar proportion of acetate and ratio of acetate to propionate were greater with yeast addition than ANT. No treatment effects on flows of organic matter (OM) and starch to the omasum were observed, whereas flows of neutral detergent fibre (NDF) were greatest with ANT, lowest with EDY and intermediate with control, ADY and MDY (P < 0.02). Digestibility of OM in the rumen tended (P < 0.09) to be less with EDY or MDY than control or ANT, but no difference in ruminal digestibility of NDF and starch was observed among treatments. In contrast, greater postruminal digestibility of OM (P < 0.01) and NDF (P < 0.03) was observed with either EDY or MDY versus control and ANT. Digestibility of OM and NDF in the total digestive tract was also greater (P < 0.01) with EDY or MDY than control. No treatment effect was observed on the flows of N to the omasum or microbial protein synthesis. Although digestibility of N in the rumen was not different, the digestibility of N in the total digestive tract was greater (P < 0.02) with EDY or MDY than control or ANT. Supplementation of ADY or MDY tended (P < 0.10) to have greater gene copy numbers of R. flavefaciens compared with ANT. Total protozoa counts were greater (P < 0.01) in the rumen of heifers supplemented with ADY or MDY compared with control or ANT. These results demonstrate the postruminal activity of ADY and indicate the potential of feeding protected yeast to ruminants to increase intestinal digestibility of nutrients. [ABSTRACT FROM AUTHOR]