PS12-11. Prepartum Rumen-Protected B Vitamin Complex Supplementation Improves Maternal Reserves, Colostrum Yield, and Reproductive Responses in Beef Cows.

Abstract

Late gestation is characterized by increased metabolic demands that may compromise maternal reserves and influence fetal development and postpartum performance in beef cows, and B-complex vitamins act as essential cofactors in oxidative metabolism, gluconeogenesis, and one-carbon metabolism, with their availability potentially becoming limiting during periods of high physiological demand despite ruminal synthesis. This study evaluated the effects of prepartum rumen-protected B-complex vitamin supplementation on maternal metabolism, body composition, colostrum production, placental traits, calving outcomes, and postpartum performance and reproductive responses in beef cows. Fifty-six pregnant Nellore cows carrying male fetuses (initial BW = 444.1 ± 12.7 kg) were maintained under grazing conditions until day 179 of gestation and then adapted to individual pens while receiving 70% of gestational requirements; from day 193 of gestation until calving, cows were assigned to either a control group (n = 28) or a B-vitamin-supplemented group (n = 28), with supplemented cows receiving the same basal diet as controls plus 3 g/cow/day of a rumen-protected B-vitamin blend (Lactation VB®, Jefo, St. Hyacinthe, QC, Canada). Data were analyzed using mixed models (PROC GLIMMIX, SAS), including treatment as a fixed effect, day and the treatment × day interaction for repeated measures, parity as a covariate, and sire as a random effect. B-vitamin supplementation did not affect circulating glucose, NEFA, or BHB concentrations (P > 0.05), nor body weight or average daily gain during late gestation (P > 0.05); however, at 43 and 15 days prepartum, supplemented cows had greater body condition score (P ≤ 0.01), ribeye area (P < 0.01), and subcutaneous fat thickness (P = 0.01) compared with controls. At calving, supplemented cows exhibited greater body weight (458.09 ± 15.23 vs. 426.29 ± 15.33 kg; P = 0.04) and body condition score (4.65 ± 0.29 vs. 3.78 ± 0.30; P = 0.01), as well as increased colostrum yield (1.86 ± 0.20 vs. 1.41 ± 0.20 kg; P = 0.03), whereas colostrum quality was not affected (P > 0.05). Placental weight was greater in supplemented cows (P = 0.04), while calf birth weight and neonatal vigor were not affected (P > 0.05). Additionally, supplemented cows had reduced odds of endometritis (P = 0.04), greater likelihood of complete uterine involution at 30 days postpartum (P = 0.02), and a tendency for increased pregnancy probability (62.9 vs. 34.8%; P = 0.06), without effects on ovarian follicular dynamics (P > 0.05); no differences were observed in average daily gain from 20 to 100 days postpartum (P = 0.36). In summary, prepartum rumen-protected B-complex vitamin supplementation improved maternal body reserves, increased colostrum yield, and enhanced uterine health and reproductive outcomes, without major effects on postpartum productive performance.