Why do trace elements have an influence on fertility?

Trace elements are essential for the function of various enzymes and other proteins. The effects of trace element biochemistry and physiology on parameters of fertility are presented for zinc, selenium, iodine, copper and manganese. Zinc ions are involved in processes of cell division, development and differentiation and in the control of gene expression. Zinc deficiency therefore affects spermatogenesis as well as embryonic development and parturition, indirect effects on fertility can be derived from the significance of zinc ions for feed intake, immune function and vitamin A metabolism. Selenium dependent enzymes protect membranes from oxidative damage and are involved in the metabolisms of prostaglandines and thyroid hormones. A selenoprotein contributes to the stability of spermatozoa. Selenium deficiency affects sperm quality and has been associated with retained placentas and metritis. Thyroid hormones contribute to ovarian function, testicular growth a nd fetal development. The Cu,Zn superoxide dismutase prevents from oxidative damage. A lack of this enzyme increases the rate of embryonic mortality. Copper deficiency affects the development of sperm cells, exposition to high copper concentrations their motility. Copper is also essential for immunity. Manganese dependent enzymes are involved in steroidogenesis, protect from oxidative damage or enhance the motility of spermatozoa. The exact diagnosis of a trace element status usually requires the measurement of several parameters. Various interactions between the trace elements and their partial toxicity implies that any supplementation should be done under controlled conditions.