PS12-15. Effects of Prenatal Vitamin A Administration on Skeletal Muscle Development and Growth of Beef Calves.

Abstract The objective of this study was to evaluate the effects of late-gestation maternal vitamin A administration on offspring growth performance, muscle gene expression, and carcass-related traits. The experiment was conducted over two years, using a total of 41 purebred Bos indicus (Tabapuã) pregnant cows. At 245 days of gestation, cows were weighed, blocked by parity and assigned to one of two treatments: control with no Vitamin A injection (CON, n = 21; 13 male and 8 female fetuses) or Vitamin A injections (VA, n = 20; 12 male and 8 female fetuses). Cows in the VA treatment received intramuscular injections of Vitamin A (2,700,000 IU) on days 245, 260, and 275 of gestation. Cows were fed a basal high-forage diet (10% CP, 50% TDN, and 35% NDF) in individual pens only from 245 days of gestation until the first week of lactation. At birth, calves were weighed and muscle samples were biopsied. Milk production was estimated daily during the first week of lactation using the weigh-suckle-weigh technique. Cow-calf pairs were managed as a contemporary group on Urochloa decumbens paddocks. At weaning (210 days of age), calves were weighed and carcass ultrasound was performed. Data were analyzed using the MIXED procedure of SAS in a randomized complete block design with a 2 × 2 factorial arrangement (two treatments and two offspring sexes). Calf birth weight was approximately 22% lesser (P = 0.05) in VA-female calves compared to all counterparts. At birth, CEBPA and MYOG expressions tended to be upregulated (P ≤ 0.09) in VA calves. Female calves tended to present greater (P = 0.08) expression of ZNF423 while males presented greater (P < 0.01) expression of MYOG. Treatment × offspring sex interactions were observed in CEBPA, PAX7, and MYF5 genes. Expression of CEBPA was greater (P = 0.02) in VA-male calves compared to all counterparts. Also, PAX7 expression tended to be greater (P = 0.09) in CON-female calves only compared to CON-male calves. And MYF5 expression tended to be greater (P = 0.06) in VA-male calves only compared to VA-female calves. No differences were observed (P > 0.41) in the estimated milk production during the first week of lactation. Male calves presented greater (P ≤ 0.05) ADG (0.765 vs. 0.698 kg/day) during the cow-calf phase and BW at weaning (190.2 vs. 167.5 kg). At weaning, longissimus muscle width tended to be 8% greater (P = 0.06) and muscling index was 19% greater (P = 0.01) in VA-treated calves. Maternal Vitamin A supplementation during late gestation altered muscle gene expression in a sex-dependent manner and improved muscling traits at weaning. These results indicate that prenatal Vitamin A may enhance muscle development and carcass potential in beef cattle.