Forehand, Lydia Rose (2019-08). EVALUATION OF THE EFFECTS OF SACCHAROMYCES CEREVISIAE (LEVUCELL) ON PERFORMANCE, PHYSIOLOGICAL, AND BEHAVIORAL RESPONSES DURING SUBACUTE ACIDOSIS IN BEEF STEERS. Master's Thesis.
The objective of this study was to evaluate the behavioral and physiological responses to live-yeast (LY) supplementation during subacute ruminal acidosis (SARA) in beef steers fed a high-concentrate diet. In the 1st study, 48 crossbred beef steers were assigned to LY or control dietary treatments, with individual-animal dry matter intake (DMI) and feeding behavior data collected daily for 70 d via an electronic feed intake measurement system. Although LY supplementation did not affect DMI or F:G, duration of BV and meal events were longer causing BV and meal eating rate to be slower in LYfed steers compared to control-fed steers. These results suggest the potential for LY supplementation to mitigate SARA in cattle fed a high-concentrate diet. In the 2nd study, 48 steers were randomly assigned to 1 of 4 treatments (n = 12): (1) control diet and nonSARA, (2) control diet and SARA, (3) LY diet and non-SARA, and (4) LY diet and SARA. Steers in the SARA treatments were subjected to SARA challenge protocols by disrupting daily DMI from 60 to 140% of baseline DMI during 7-d periods. Steers were placed in pens equipped with the GrowSafe System and weighed weekly to evaluate the effects of LY supplementation during imposed SARA challenges on DMI, feeding behavior patterns, and performance. Six steers per treatment were fitted with reticulorumen boluses to measure rumen pH and temperature. In general, the SARA treatment caused reductions in mean, maximum and minimum ruminal pH and increased daily variance of pH and duration and AUC of pH < 5.8, confirming that the experimental SARA challenge protocols disrupted the rumen environment. Live-yeast supplementation consistently reduced DMI and F:G throughout the trial and increased mean and minimum ruminal pH, while decreasing daily variance of ruminal pH and duration and AUC of pH < 5.8. Significant diet x SARA interactions illustrated the benefit of supplementing LY during SARA, such that LY supplementation increased mean and maximum ruminal pH in SARA-treated steers, but not in non-SARA steers. Additional, LY supplementation decreased duration and AUC of pH < 5.8 to a greater extent in SARA-treated steers than in non-SARA steers (diet x SARA interactions; P < 0.01). Results from this study demonstrate the efficacy of the experimental SARA challenge protocols, and that LY supplementation favorably altered the rumen environment, especially during SARA challenges.