PS4-2. Triticale Silage Used as Ruminal in Situ Substrate to Assess the Effects of Saccharomyces Cerevisiae in Beef Cattle Grower and Finisher Diets.

Abstract Ruminal degradability kinetics of triticale silage (in situ substrate) of beef steers consuming beef cattle grower and finisher diets with or without (live yeast) Saccharomyces cerevisiae were evaluated. Eight surgically prepared beef steers were used in a duplicated 4 × 4 Latin square design (four 38-day periods) following a 2 × 2 factorial arrangement of treatments: A) presence of live yeast (Saccharomyces cerevisiae [CNCM I-1077], at 1 × 1010 CFU/animal-daily); and B) diet type (steam-flaked corn-based grower or finisher diets [ad libitum intake]). Live yeast was delivered via gel capsules (0.25 g, as-is) twice daily through the ruminal cannula. Pre-dehydrated (55ºC for 72 h) triticale silage substrate was ground (2 mm) and placed into 10 × 20 cm (28 µm) nylon bags (5g, as-is). Bags were placed in the ruminal ventral sac within a nylon mesh (with weights) and reversely removed at 0, 2, 4, 8, 12, 20, 32, 48, 64, 72, and 96 h after incubation. Residue bags were rinsed and dehydrated for 72 h at 55ºC. Residue duplicates were composited, corrected for moisture, 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 inclusion tended (Diet × Yeast interaction, P = 0.06) to increase the rate of degradation and the effective degradability calculated at 4, 5, and 6 %/h of the substrate organic matter (OM) when offered in finisher diets, while not affecting such fractions in grower diets. Regardless of diet type, live yeast increased the substrate dry matter (DM) rate of degradation (P = 0.04), tended (P = 0.10) to increase the effective degradability of the DM fraction (calculated at 4%/h rate of passage), and tended (P = 0.11) to decrease the substrate hemicellulose fraction lag-time (h). Regardless of live yeast inclusion, steers offered the grower diet had greater (P < 0.01) triticale silage substrate potentially degradable fraction, lesser undegradable (P < 0.01), and greater (P < 0.01) effective degradability calculated at 4, 5, and 6 %/h rate of passage for DM, OM, NDF, ADF, and hemicellulose fractions, while also tending (P = 0.11) to increase the substrate DM rate of degradation compared to finisher diets. The current ruminal in situ model replicated expected results between beef cattle steam-flaked corn-based grower and finisher diets when using a forage substrate. Live yeast seemed to improve ruminal effective degradability of a high-quality forage substrate (triticale silage) OM fraction in a beef cattle finisher diet more intensively than in a grower diet, while other positive effects were observed regardless of diet type.