Vitamins and minerals affect reproductive function. Vitamin A deficiency has long been known to affect reproductive function in cattle. More recently, a role has been proposed for the vitamin A percursor, beta-carotene, in reproductive efficiency. Dietary supplementation with vitamin E and selenium may reduce the incidence of retained placenta, but these nutrients may also affect reproductive function in other ways. Calcium and phosphorus deficiencies affect reproduction in cattle, and vitamin D may directly affect reproductive function in addition to its role in calcium and phosphorus metabolism. Dietary manipulation of a number of other vitamins and minerals also influences reproductive function. However, the specific roles of nutrients in reproductive tissues are not well-defined in dairy cattle, and nutrient requirements for optimal reproductive efficiency in modern dairy cattle deserve careful reevaluation. This review provides a background of the effect of vitamins and minerals on reproduction and it attempts to provide a basis for further investigation of specific mechanisms by which reproductive function is affected. The interface between nutritional science and reproductive physiology provides considerable potential for optimizing reproductive efficiency in dairy cattle.

The role of relaxin in mammary development was studied between days 80-110 of pregnancy in ovariectomized gilts given progesterone to maintain pregnancy. To obtain an objective measurement of lobulo-alveolar (parenchymal) composition, mammary glands were cut in cross-section through the teat, and the area of parenchymal tissue on the exposed face of the gland was determined. Ovariectomy on day 80 or 100 followed by progesterone replacement therapy resulted in a dramatic reduction in the rate of growth of mammary parenchymal cross-section area on days 100 and 110 of gestation, respectively, compared to that in controls. In contrast, progesterone plus relaxin therapy, with highly purified porcine relaxin, restored the mammary parenchymal cross-section area to control values in ovariectomized gilts. Morphometric analysis of mammary tissue on day 110 of pregnancy indicated that both the absence of relaxin after ovariectomy and replacement therapy with porcine relaxin in ovariectomized gilts had little if any effect on the percentages of the lumen, stroma, or epithelial that comprised the mammary parenchyma. It is concluded that relaxin has a stimulatory effect on the growth of mammary parenchymal tissue during late gestation in the pig.