11 Evaluating Relationships Between Plasma and Liver Retinol Concentrations in the Beef Cow and Calf

Abstract

Abstract In the young calf, vitamin A is particularly important for immune system maturation, and calves rely on colostrum at birth to supply vitamin A. Cow vitamin A status may influence colostral vitamin A concentrations, which can impact vitamin A status of their calves. Very little is understood about this relationship between beef cow and calf vitamin A status. Furthermore, limited data is available on how plasma and liver retinol concentrations in cattle are related to one another. The objective of this study was to examine relationships between liver and plasma retinol concentrations in the cow, calf, and within cow-calf pairs. Multiparous MARC II beef cows (n = 120; 6.4 ± 1.2 SD years of age; 592 ± 58 SD kg BW) in mid-gestation were provided supplemental vitamin A as retinyl acetate in a supplemental pellet at a rate of 21,125 ± 8,560 SD IU/d (current NASEM recommendation = 33,000 IU/d). Cows were individually fed using Calan gates a diet consisting of alfalfa hay, corn silage, and supplemental pellet for 144 d (111 d pre-calving and 32 d post-calving). Basal diet vitamin A concentration was 490 IU/kg of DM. Mean initial liver concentration of cows was 830 µg retinol/g of DM. To assess vitamin A status, liver biopsies and plasma samples were collected on cows and calves at the end of the supplemental period when calves averaged 32 ± 7 days of age (DOA). Pearson correlations were used to test for linear relationships between cow liver and plasma retinol concentrations, calf liver and plasma retinol concentrations, and liver and plasma retinol concentrations between the cow and her calf. No linear relationship (P = 0.10; r=0.16) was observed between liver and plasma retinol in cows. In the present study, mean cow liver retinol concentration (482 ± 182 SD µg/g of DM) fell within the current adequacy reference range of 300–700 µg/g of DM. Cow plasma retinol (272 ± 40 SD ng/mL) was slightly below the reference range of 300–800 ng/mL. A positive correlation (P < 0.01; r=0.37) was detected between calf liver (51 ± 27 SD µg/g of DM) and plasma (190 ± 47 ng/mL) retinol concentrations. Both were below what would be considered adequate (100–350 µg/g of DM in liver; 225–325 ng/mL in plasma) for calves at 32 DOA. There was a positive correlation (P < 0.01; r=0.31) between cow and calf liver retinol, suggesting that as cow retinol liver concentrations increased, calf liver retinol concentrations increased. It appears that despite cows having adequate liver retinol concentrations when 21,125 IU vitamin A/d was fed, it did not result in calf liver retinol stores that would be considered adequate given current reference ranges. USDA is an equal opportunity employer and provider.