PS5-6. Saccharomyces Cerevisiae and Its Effects on Ruminal Degradability Kinetics of a Low-quality Crop Residue on Beef Steers Offered Grower and Finisher Diets.

Abstract The effects of live yeast inclusion and beef steer diet type on ruminal degradation kinetics of a corn stalk substrate were evaluated. Eight ruminally cannulated beef steers were utilized in a duplicated 4 × 4 Latin square design within a 2 × 2 factorial arrangement of treatments, as follows: A) presence of live yeast (Saccharomyces cerevisiae [CNCM I-1077], 1 × 1010 CFU/animal-daily); and B) diet type (steam-flaked corn-based grower or finisher diets [ad libitum intake]). Live yeast was placed in gel capsules (0.25 g, as-is) twice daily via the ruminal cannula. Pre-dehydrated (55oC for 72 h) corn stalks were ground (2 mm) and placed into 10 × 20 cm (28 μm) nylon bags (5 g, as-is). Substrate bags were placed within a nylon mesh into the rumen and reversely removed at 0, 2, 4, 8, 12, 20, 32, 48, 64, 72, and 96 h after incubation. Bags were rinsed, dehydrated for 72 h at 55oC, organized by steer, period, and incubation time, and used to fit a first-order kinetics model using the NLIN procedure of SAS. The GLIMMIX procedure of SAS was used with animals as the experimental unit, the fixed effects (diet, period, interaction), and the random effects of animal ID within square, square, and period. Live yeast tended (P = 0.09) to increase the substrate ADF rate of degradation on grower diets while decreasing for finisher diets. Regardless of dietary type, live yeast increased (P ≤ 0.04) corn stalk effective degradability (ED) of organic matter (OM), NDF, and hemicellulose at 4, 5, and 6%/h rate of passages; and tended (P ≤ 0.10) to increase ED of dry matter (DM) at 4 and 5%/h; while not affecting (P ≥ 0.47) ED for the ADF fraction. Live yeast did not affect substrate lag time (P ≥ 0.25) or soluble, potentially degradable, and undegradable fractions (P ≥ 0.21) of nutrients, except by a tendency (P = 0.08) for a lower hemicellulose undegradable fraction. Regardless of live yeast inclusion, the substrate potentially degradable fraction of DM, OM, and fiber fractions increased (P < 0.01) when exposed to grower diets, while the undegradable portion of such fractions decreased (P < 0.01) in such a diet type. Substrate lag time was not affected (P ≥ 0.23) by diet type, while only few non-meaningful differences were observed for the soluble fraction. The model replicated expected results between grower and finisher diets when using a low-quality substrate. Live yeast improved the effective degradability of the corn stalk crop residue substrate regardless of diet type, while the ADF fraction of such a substrate within a grower diet with live yeast seemed to speed up its rate of degradation, and the opposite was observed within a finisher diet.