RESEARCH PAPERS Possible Role of Beta-Carotene in Improving Fertility in Dairy Cattle 1,2

Recent interest in /3-carotene has been stimulated by reports that reproductive performance in cattle was improved with dietary supplementation of /3-carotene even when the diet was supplemented with vitamin A. Vitamin A requirements for cattle are based on studies with /3carotene as the vitamin A source and with studies with vitamin A in the ester or alcohol form. Most of the studies with cattle that demonstrate the need for vitamin A for optimum reproduction were when /3-carotene was the source of vitamin A. Recent German reports show an improvement in conception rate, intensity of estrus, and changes in luteinizing hormone patterns when cattle received /3-carotene supplementation of low carotene diets. These diets were supplemented with vitamin A. A similar study from Israel did not detect benefits of/3carotene. The active form of vitamin A for reproduction in rats and other species has not been determined; however, vitamin A does meet the reproductive requirements. The ruminant animal does have differences in carotene metabolism from the rat. Before the role of/3-carotene for reproduction in cattle can be clarified, the specific function of carotene or the specific form of vitamin A for reproduction needs to be determined. Received October 19, 1981. Invitational paper presented at the 76th Annual Meeting of the American Dairy Science Association, June 29, 1981. 2 This manuscript (81-5-201) is published with the approval of the Director of Kentucky Agricultural Experiment Station. DISCUSSION Recent publications from Germany (1, 20, 21, 22, 25, 31, 32) have stimulated a renewed interest in /3-carotene for ruminant animals. They reported improved reproductive performance for cattle supplemented with /J-carotene even when the diet was supplemented with vitamin A. Prior to these reports, it was assumed that vitamin A fed adequately as retinyl esters would eliminate reproductive problems associated with this vitamin. These reports suggest a requirement for /3-carotene that cannot be met as supplemental A. Vitamin A has been established as essential for vision, growth, reproduction, and maintenance of differentiated epithelia and of mucous secretion. The main emphasis of this review will be concerned with the role of/3carotene and vitamin A for reproduction. Other aspects of vitamin A metabolism will be discussed to show the need for clarification of vitamin metabolism before the role of /3carotene for optimum reproduction can be