PS12-20. Effects of vitamin A administration in beef cows during late gestation on maternal performance, placental parameters, and lactation.

Abstract The objectives were to evaluate the effects of late-gestation maternal Vitamin A administration on placental development and gene expression, maternal performance, and lactation 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. Cows were weighed on days 245, 260, 275 of gestation, at parturition to estimate the gain of gestational components, and at weaning (210 days). At parturition, the placenta was immediately weighed, and cotyledons were sampled for gene expression analysis. Milk production was measured and milk samples were collected on days 15, 30, 45, 73, and 101 in milking. Cow-calf pairs were managed as a contemporary group on Urochloa decumbens paddocks. Data were analyzed using the MIXED procedure of SAS in a randomized complete block design with a 2 × 2 factorial arrangement. At 275 days of gestation, CON cows tended to present greater (P = 0.09) BW. Gestation length was influenced by treatment and fetus sex, where VA-treated cows carrying female fetuses tended to present fewer (P = 0.07) days of gestation compared to VA-cows carrying male fetuses and CON cows carrying female fetuses. Total gain of gestational components tended to be greater (P = 0.09) in CON cows. Cows carrying male fetuses exhibited greater (P ≤ 0.05) gestational gain and placental weight. The expression of STRA6 in the cotyledon was upregulated (P = 0.04) in VA-treated cows carrying female fetuses. The cotyledon of the placenta from female fetuses exhibited greater (P ≤ 0.03) expressions of VEGFA and SLC5A1. No treatment differences were observed in cow BW or ADG from parturition until weaning (P > 0.36). During lactation, VA-treated cows nursing male calves showed an increase (P = 0.02) in milk yield compared to all their counterparts. In addition, VA-treated cows presented greater (P ≤ 0.03) milk fat and protein contents. Maternal vitamin A supplementation during late gestation modulated placental gene expression in a sex-dependent manner and improved milk yield and composition, particularly in cows nursing male calves. Our findings indicate that Vitamin A influences placental function and lactation performance, potentially enhancing nutrient supply to the offspring.