124 Effects of <i>Saccharomyces cerevisiae</i> and dietary type offered to beef cattle on intake, feeding behavior, nutrient digestibility, and ruminal fermentation

Abstract The effects of live yeast and diet type offered to beef steers on intake, feeding behavior, nutrient digestibility, and ruminal fermentation profile were evaluated. Ruminally cannulated beef steers [n = 8; body weight (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 CFUּ animal-1ּ d-1]; and B) diet type [steam-flaked corn-based grower or finisher diets (ad libitum intake)]. Live yeast was delivered with gel-capsules (0.25 g, as is) twice daily via ruminal-cannula. Four, 35 d periods were used. Feed refusal was subtracted from offered (dry matter basis) to calculate feed intake (DMI). The 24 h feeding behavior assessment was conducted on d 31 by trained personnel (time spent eating, ruminating, chewing, drinking, resting, and meal size/number). A 5-d fecal collection (twice daily) was used for the digestibility assessment. Ruminal pH was continuously measured (7 d, intra-ruminal Dascor wireless data loggers). Ruminal ammonia-N and volatile fatty acids (VFA) were analyzed at 0, 2, 4, 8, 16, and 23 h on d 35. The GLIMMIX procedure of SAS was used with animals as the experimental unit. No live yeast × diet interactions (P ≥ 0.17) were observed. Intake was not affected (P = 0.83) by live yeast, while steers offered the grower diet consumed more (P ≤ 0.01) NDF, ADF, and hemicellulose compared with the finisher diet. Live yeast increased (P ≤ 0.02) the dietary NDF, ADF, and hemicellulose digestibility of the grower diet by 13.7, 12.8, and 14.6%, and on the finisher diet by 6.7, 9, and 6.4%, respectively. Live yeast did not affect (P ≥ 0.23) major feeding behavior activities measured. Steers offered grower diet spent more time (P ≤ 0.01) on each meal, ruminating, eating, and chewing and less time (P &amp;lt; 0.01) resting. Live yeast did not affect (P ≥ 0.81) ruminal pH variables measured. Steers offered the grower diet had a greater (P &amp;lt; 0.01) ruminal pH pattern compared with the finisher diet. The ruminal ammonia-N and volatile fatty acids were not affected (P ≥ 0.16) by live yeast, while steers offered the finisher diet had a greater (P ≤ 0.01) total VFA and propionate molar proportion, while a lower (P ≤ 0.01) ammonia-N and acetate molar proportion compared with the grower diet. Regardless of the diet type, live yeast improved digestibility of fiber fractions, while dry matter intake was unaffected. Grower diets were more prone to stimulate feeding behavior activities than finisher, while live yeast seemed to not affect such variables. Expected effects of diet type on ruminal fermentation were ratified, while live yeast inclusion did not affect the ruminal fermentation variables evaluated.