PSXIII-24 Performance and blood characteristics of beef heifers supplemented with yeast during the prepubertal period.

Abstract During the period preceding the first ovulation in heifers (prepubertal period), several physiological and metabolic changes occur which may impact reproductive efficiency. Body weight (BW) and metabolic markers such as insulin-like growth factor 1 (IGF-1) and glucose, play a crucial role in these processes. For Bos indicus heifers, it is recommended to achieve at least 60% of mature BW before initiating reproductive protocols. Nutritional strategies that optimize BW and metabolic responses may enhance reproductive efficiency. This study aimed to evaluate the effects of different yeast types in an energy-protein supplementation regime on the performance and metabolic profile of Bos indicus beef heifers under grazing regime during the prepubertal period. Thirty-six Nelore heifers (initial BW of 263.6 ± 2.7 kg; 12 ± 0.09 months old) were randomly assigned to one of three dietary treatments: T1 - soluble fermentation solids (yeast cell wall), T2 - Saccharomyces cerevisiae, and T3 - Saccharomyces boulardii. Heifers were supplemented with an energy-protein supplement mix (6 g/kg BW) containing 20% crude protein, 69.12% corn, 18.58% soybean meal, and 12.30% commercial mineral premix. The trial lasted 120 days, consisting of 60 days of performance and 60 days of reproductive efficiency evaluations. Performance data, including BW and average daily gain (ADG), were collected on days 60 and 120. Carcass ultrasonography assessed at the Longissimus dorsi rib-eye area (REA), subcutaneous fat thickness at the 9th-12 th rib (SFTrib) and at the rump (SFTrump). Blood samples were collected on days 60 and 120 were analyzed for glucose, blood urea nitrogen (BUN), and IGF-1concentrations. Data were analyzed using the MIXED procedure of SAS, and statistical significance was declared at P ≤ 0.05. A significant treatment x time interaction was observed for BW (P = 0.018), while ADG was higher during the reproductive period (P = 0.02). No treatment effects were detected for REA (P > 0.05), whereas SFTrib and SFTrump increased over time (P < 0.01). Glucose and BUN levels increased (P = 0.02 and 0.04) whereas IGF-1 concentrations declined (P < 0.05) throughout the trial. In conclusion, yeast supplementation did not significantly influence performance or metabolic markers in grazing Bos indicus beef heifers during the prepubertal period. The observed effects likely reflect the overall availability of nutrients in the provided nutritional plane rather than the direct effect of yeast supplementation. Further research is needed to determine potential long-term reproductive implications of these metabolic shifts.