Maternal Vitamin a Supplementation Effects on Beef Calf Vitamin a Concentrations

Angus cows (n = 48; 7.3 ± 1.7 years of age) freshly off pasture were used to investigate the relationship between maternal vitamin A status and intake, and the resulting vitamin A status of neonatal calves. Cows were stratified by initial liver retinol (882 ± 218 mg/g DM), age, and expected calving date to one of three treatments of targeted supplementation of vitamin A/d: 1) 0 IU, 2) 33,000 IU, 3) 99,000 IU. Treatments were administered using a SuperSmartFeed unit (C-Lock, Inc., Rapid City, SD) as a pelleted supplement meeting all other NASEM (2016) trace mineral and vitamin requirements with targeted intake of 0.45 kg/d. Vitamin A was supplemented as retinyl acetate (ROVIMIX A 1000; DSM Nutritional Products; Pendergrass, GA). The basal diet consisted of free choice alfalfa/grass hay mix. Supplementation started 45 ± 15d prior to calving and ended at time of calving. Liver and plasma samples were collected from all cows on 238 ± 15d of gestation (pre-calving) and 16 ± 5d after calving. Body weight and body condition score were recorded. Plasma samples were collected from calves at ∼24h, and plasma and liver collected at 16 ± 5d of age. Samples were analyzed for retinol concentration. Assigned treatments were ignored due to large variation in supplemental vitamin A intake in each treatment (TRT 1: 0 IU/d; TRT 2: 0-31,000 IU/d; TRT 3: 29,000-85,000 IU/d). Average cow and calf liver retinol at 16d post-calving was 705 ± 231 mg/g DM and 36 ± 16 mg/g DM, respectively. Calf plasma retinol (∼24h) concentration was 149 ± 42 mg RE/L. Data were analyzed using multiple linear regression in R Statistical Software 4.4.1. Stepwise AIC was used for variable selection. The first model included calf plasma retinol ∼24h after birth as the dependent variable and included cow pre-calving liver retinol and cow age as independent variables (R2 = 0.25). Cow pre-calving liver retinol and cow age explained 18% and 7% of the variation, respectively (P = 0.01). The second and third models included 16d calf liver retinol as the dependent variable. The independent variable for the second model was calf 16d plasma retinol concentration, which, though significant, explained only 10% of the variability (P = 0.03; R2 = 0.10). Independent variables for the third model were cow 16d plasma retinol concentration and total supplemental vitamin A intake (R2 = 0.27). The third model explained more of the variability in 16d calf liver retinol, with cow 16d plasma retinol and total supplemental vitamin A intake contributing 14% and 13%, respectively (P = 0.01). In this study, maternal status and vitamin A intake influenced calf liver retinol, but high residual variation warrants further work to identify the unmeasured factors affecting calf liver retinol.