Trace Mineral Function

Zinc. Zinc is an essential component of over 200 enzyme systems of which the metabolic actions include carbohydrate and energy metabolism, protein synthesis, nucleic acid metabolism, epithelial tissue integrity, cell repair and division, and vitamin A and E transport and utilization (14). In addition, it plays a major role in the immune system and certain reproductive hormones (14).

Zinc is known to be essential for proper sexual maturity, reproductive capacity, and more specifically, onset of estrus (25). Zinc has a critical role in the repair and maintenance of the uterine lining following parturition, speeding return to normal reproductive function and estrus (25). In bulls, a zinc deficiency results in poor semen quality and reduced testicular size and libido (20, 29, 39). Zinc has also been shown to increase plasma beta carotene levels (58). Increased plasma beta carotene has been directly correlated to improved conception rates and embryonic development.

Improved zinc status also improves fertility by reducing lameness, resulting in cows more willing to show heat and improved mobility and performance of bulls. Inadequate zinc supplementation results in mild to severe claw (hoof) disorders, including weak claws that are more susceptible to interdigital and digital dermatitis and foot rot (52).

The recommended dietary content of zinc for dairy cattle is typically between 18 and 73 ppm depending upon stage of the life cycle and dry matter intake (46). Copper, cadmium, calcium and iron reduce zinc absorption and interfere with zinc metabolism (52).

Manganese. In general, manganese is an activator of enzyme systems in the metabolism of carbohydrates, fats, proteins and nucleic acids (52). It is also essential for normal brain function, and plays a role in collagen formation, bone growth, urea formation, synthesis of fatty acids and cholesterol and digestion of protein (30, 33).

Manganese appears to have a vital role in reproduction. It is necessary for cholesterol synthesis (33), which in turn is required for synthesis of the steroids, estrogen, progesterone and testosterone. Insufficient steroid production results in decreased circulating concentrations of these reproductive hormones resulting in abnormal sperm in males and irregular estrous cycles in females (8). The corpus luteum has a high manganese content and may be affected by level of manganese supplementation. Also, vaginal manganese concentrations are higher in cycling than in anoestrous ruminants (41). A deficiency in manganese may be associated with suppression of estrus, cystic ovaries and reduced conception rate (52)

Table 1. Impact of Trace Mineral Deficiency on Ruminant Reproduction

The manganese requirement of weaned dairy cattle typically ranges between 13 and 22 ppm depending upon stage of the life cycle and dry matter intake (46). Levels of manganese considered adequate for growth in ruminants have been known to be associated with anoestrous, subestrus and reduced conception rates (17). By feeding manganese at increased levels, researchers have been able to minimize these problems. Dietary excesses of calcium and potassium increase manganese requirements due to increased fecal losses (41). Iron, magnesium, phosphorus and cobalt also reduce the availability of manganese (52).