255 Awardee Talk: Nutritional management to optimize cow-calf production in Southeast

Abstract Nearly one-half of beef cows in the United States are located in southern states where cow-calf operations predominate. Grazing management in cow-calf systems can be affected by environmental and seasonal conditions, often leading to nutrient deficiency, particularly during late gestation of beef females. Maternal nutrition during the last trimester of gestation can influence offspring development and health, and can be explored to optimize maternal and progeny performance. The objective of this presentation is to share nutritional and management strategies for pregnant beef cows and their long-term effects on offspring growth and physiology. Study 1 investigated the effects of timing of maternal protein supplementation during all last trimester of gestation (LATE84), only the first 42 d of last trimester of gestation (LATE42), or no prepartum supplementation (NOSUP) on offspring pre- and post-weaning performance. At weaning, LATE84 calves were the heaviest, followed by LATE42, and NOSUP (P ≤ 0.05). Steer serum parainfluenza-3 titers were greater (P = 0.03) for LATE42 vs. NOSUP and tended to be greater for LATE84 (P = 0.10) vs. NOSUP steers. Marbling and the proportion of steers grading choice were greater (P ≤ 0.04) for LATE42 vs. NOSUP, and intermediate for LATE84. Study 2 evaluated the effects of frequency of maternal protein supplementation on offspring pre-weaning growth. Cows received the same weekly amount of supplement (7 kg·cow⁻¹·wk⁻¹) but with different frequencies: once a week (1X), three times per week (3X), every day (7X), or no prepartum supplementation (NOSUP) during the last 80 d of gestation. At weaning, calves born from 7X cows were the heaviest (P ≤ 0.05), followed by 3X and 1X, which did not differ between them (P = 0.54), and NOSUP calves were the lightest (P ≤ 0.05). Study 3 evaluated the use of monensin supplementation during the last 77 d of gestation and its impacts on offspring performance. Treatments consisted of no prepartum supplementation (NOSUP), supplementation of dried distillers grains at 1 kg·cow⁻¹·d⁻¹ added with 0 (SUP) or 200 mg/d of monensin (SUPMO). At weaning, SUPMO calves were the heaviest (P ≤ 0.05), SUP intermediate, and NOSUP were the lightest. Experiment 4 consisted of pregnant heifers receiving the supplementation of 1 kg/d of soybean hulls dry matter added (BAC) or not (CON) with a Bacillus-based DFM mixture during late gestation (d 0 to 139) and early lactation (d 139 to 242). Post-weaning body weight gain and indicators of humoral immune response post-vaccination were greater for BAC vs. CON calves (P ≤ 0.05). Therefore, changing the time and frequency of supplementation, and the use of additives and probiotics during late gestation of beef females are effective alternatives to improve offspring pre- and post-weaning growth and immune response.