THE STATUS OF BETA-CAROTENE AND VITAMIN A IN QUEBEC DAIRY HERDS: FACTORS AFFECTING THEIR STATUS IN COWS AND THEIR EFFECTS ON REPRODUCTIVE PERFORMANCE

Abstract

Feed samples and a milk sample from the bulk tank were obtained from 100 randomly selected Holstein herds on the official option of the Dairy Herd Analysis Service, and jugular blood samples were obtained from five cows within each herd. Feed, milk and blood samples were analyzed for beta-carotene and grains, supplements, milk and blood for vitamin A. Haylage appeared to be the most reliable source of beta-carotene in comparison to dry hay and corn silage. The acid detergent fiber content of hay and/or haylage was shown to be negatively correlated to beta-carotene concentration. The concentrations of beta-carotene in the diet, plasma and milk were shown to be positively correlated; the same trends were observed for vitamin A. The concentrations of beta-carotene and vitamin A in plasma were shown to be negatively related. Factors affecting the concentrations of beta-carotene and vitamin A in plasma were examined. The beta-carotene and vitamin A status of a herd were shown to be both negatively correlated to calving interval and number of breedings per conception. Beta-carotene may only be expected to improve the fertility of a dairy herd when it is the most limiting factor. Additionally, the vitamin A status of a herd should always be considered when evaluating its beta-carotene status. Key words: Beta-carotene, vitamin A, reproductive performance, forage quality, cows (dairy)