53 Effect of Vitamin A Supplementation During Gestation on Vitamin A Status of Beef Cows and Their Calves Managed in the Drylot

Abstract

Abstract Cows fed diets consisting primarily of stored forages and concentrates may be at risk for vitamin A deficiency because these feedstuffs are low in β-carotene. Furthermore, dietary vitamin A concentrations of the cow during late gestation will affect vitamin A concentrations in colostrum, which calves rely on at birth to supply vitamin A. The objective of this study was to evaluate how level of vitamin A supplementation from mid-gestation to early lactation affected cow and subsequently, liver retinol concentrations of their calf. Multiparous beef cows (n = 54) were stratified by body condition score and previous source and assigned to pen (n = 9); 3 pens were assigned to each of the following treatments: current NASEM recommendation (31,000 IU/d; 1X), 3 times (93,000 IU/d; 3X), or 5 times (155,000 IU/d; 5X) the current NASEM recommendation for supplemental vitamin A. Cows were limit-fed a diet consisting of wheat straw, corn silage, and wet distillers grains. Liver biopsies were collected on cows 3 weeks before treatment initiation, d 40 and d 81 of supplementation, and both cows and calves were sampled 32 days post-calving (165 ± 22 d SD of supplementation). No differences (P=0.86) in initial cow liver retinol (mean 186 µg/g DM) were observed between treatments. A significant treatment × day interaction (P < 0.01) was observed for cow liver retinol. On d 40, cows in 1X had liver retinol concentrations (178 µg/g DM) that were not different (P = 0.12) from 3X (213 µg/g DM) but less (P = 0.02) than 5X (241 µg/g DM), while 3X and 5X did not differ (P = 0.21). Liver retinol on d 81 was less (P < 0.05) in 1X (189 µg/g DM) compared with 3X (334 µg/g DM) and 5X (412 µg/g DM), which did not differ (P = 0.20). For cow liver retinol post-calving, 1X (187 µg/g DM) was less (P< 0.05) than 3X and 5X, and 3X (454 µg/g DM) was less (P< 0.05) than 5X (674 µg/g DM). Liver retinol concentrations of 1X cows remained below adequate reference ranges (300–700 µg/g of DM) throughout the study, whereas 3X and 5X were increased into the adequate range by d 81. Calf liver retinol concentration also differed among treatments (P = 0.01), as calves of cows in 1X had less (P < 0.05) liver concentrations than 3X and 5X calves which did not differ (P=0.12). Liver retinol concentrations considered adequate for calves at 32 days of age (100–350 µg/g of DM) were not observed in 1X calves (51 µg/g DM) but were observed in calves from 3X and 5X cows (119 and 165 µg/g DM, respectively). Supplementing cows with 93,000 IU/d of vitamin A for 165 days brought liver retinol concentrations of cows and their calves up within adequate reference ranges.