PS3-4. Effects of Autolyzed Yeast on Growth Performance, Health, and Complete Blood Count of Newly Received High-Risk Feedlot Heifers.

Abstract The objective of this study was to determine the effects of feeding an autolyzed yeast product on growth performance and health outcomes of high-risk receiving heifers. Newly received, high-risk heifers (n = 450) were randomly assigned to 1 of 3 dietary treatments: 1) a common receiving diet containing no yeast product (CON), 2) the CON diet with 9 grams/heifer/d of autolyzed yeast (RY40-9; RumenYeast40, ICC Animal Nutrition, São Paulo, Brazil) and 3) the CON diet with 14 grams/heifer/d of autolyzed yeast (RY40-14; RumenYeast 40, ICC Animal Nutrition). The study was a randomized block design consisting of 45 pens in 15 body weight (BW) blocks (3 pens per block, 15 replicated pens per treatment). Individual BW were measured on d 0, 14, 28, and 56. Concomitant with BW measurements, 3 heifers per pen were selected as a sample subset and serum was collected via jugular venipuncture for analysis of complete blood cell count (CBC).Treatment differences were considered statistically significant for performance, health effects, and CBC parameters when P ≤ 0.05 and a tendency when 0.05 < P ≤ 0.10. No differences were observed for BW (P ≥ 0.54) or average daily gain (ADG; P ≥ 0.22) for any of the time periods evaluated throughout the study. In contrast, dry matter intake (DMI) was less for RY40-14 than RY40-9 and CON from d 0 to 14 (P = 0.01) and d 0 to 28 (P = 0.05), but G:F did not differ (P ≥ 0.12) among treatments. No treatment differences were observed for health outcomes including first treatment (P = 0.12), second treatment (P = 0.40), or third treatment (P = 0.42) for bovine respiratory disease, relapse rate (P ≥ 0.74), or antimicrobial treatment cost (P = 0.15). A treatment × day interaction (P ≤ 0.05) was observed for red blood cell and hemoglobin concentrations where RY40-9 was greater than CON on d 56. On d 56, hematocrit was greater for both RY40-9 and RY40-14 vs. CON (treatment × day; P = 0.03). White blood cell and lymphocyte concentrations tended to be less for RY40-14 than RY40-9 and CON on d 28 (treatment × day; P ≤ 0.09). The results of this study indicate feeding autolyzed yeast to high-risk feedlot heifers does not influence BW, ADG, or clinical health outcomes, yet may impact immune-associated biomarkers such as white blood cell and leukocyte concentrations.