Abstract The effects of live yeast inclusion and beef cattle diet type on ruminal degradation kinetics of “WW-B Dahl” Old World bluestem (Bothriochloa bladhii Retz T. Blake) substrate were evaluated. Ruminal cannulated Angus crossbred steers (n = 8, BW = 550 ± 20 kg) were used in a duplicated 4 × 4 Latin square design 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 placed in gel capsules (0.25g, as-is) twice daily via the ruminal cannula. Pre-dehydrated (55C for 72 h) WW-B Dahl was ground (2mm) and placed into 10 × 20 cm (28μm) nylon nags (5g, as-is). The 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 55C and composited by steer, period, and incubation time, and used to fit a first-order kinetics model using the NLIN procedure of SAS (animal as the experimental unit). No interaction (P ≥ 0.17) diet × yeast was observed for ruminal degradability variables. Regardless of dietary type, live yeast increased (P = 0.02) the rate of degradation (kd, %/h) of WW-B Dahl substrate NDF and tended (P = 0.12) to increase for hemicellulose; decreased (P = 0.05) the lag time for dry matter (DM) and tended to decrease for NDF (P = 0.06) and ADF (P = 0.08); and tended (P ≤ 0.14) to increase the effective degradability (ED) of NDF (at a kp rate of passage of 5 and 6%/h) and hemicellulose (P ≤ 0.12; kp of either 4, 5, or 6 %/h). Regardless of live yeast inclusion, steers offered the grower diet had greater (P 0.01) WW-B Dahl substrate potentially degradable (B) fraction, ED (kp at 4, 5, or 6%/h), and lesser undegradable (C) fraction for DM, organic matter (OM), NDF, ADF, and hemicellulose; greater (P ≤ 0.05) lag time for DM, OM, and hemicellulose, while lesser (P 0.01) lag time for ADF, compared to steers offered the finisher diet. Treatments did not affect (P ≥ 0.23) WW-B Dahl substrate rate of degradation of DM, OM, and ADF; while only subtle differences were observed for the soluble fraction (A). The model replicated expected results between grower and finisher diets when using a low-quality forage substrate. Live yeast improved the ruminal degradation kinetics of WW-B Dahl, especially those related to fiber fractions, as well as tending to trigger overall dry matter, NDF, and ADF degradation sooner than diets without live yeast.
Martinez et al. (Wed,) studied this question.