What minerals are tied to reproduction in beef cattle?

Beef Cattle February 19, 2008|Print
Phosphorus, calcium, copper, cobalt, iodine, selenium, zinc, and manganese are all involved in governing successful reproduction. Since mineral availability varies by region, consult your local county Cooperative Extension agent for more information regarding your area. In formulating cow diets, one important mineral to consider that maintains normal reproductive function is phosphorus. Phosphorus supplementation is important in most parts of the United States, but it becomes more important in areas of the country where cattle are maintained on grazed forage year around. Thus, in areas of the country such as Arizona, New Mexico, Texas, and Oklahoma, phosphorus deficiency is more likely to be observed than in parts of the country where cows are routinely maintained on summer grass and then fed harvested forage during the winter months, both of which often contain adequate phosphorus. The phosphorus supplementation program you use should be influenced by the phosphorus content of the forage being fed and the requirements of the cow. The trace elements most likely to influence reproduction in cattle are copper, cobalt, iodine, selenium, zinc, and manganese, deficiencies of which can occur in the grazing ruminant and affect reproductive performance or related important economic production parameters. Other elements such as iron and molybdenum can be important considerations but seldom from a deficiency standpoint. In both cases, excesses can have an impact on the animal, most notably by their negative impact on copper utilization. Copper (Cu) is involved in numerous body physiological functions such as hemoglobin formation, iron absorption and mobilization, and connective tissue metabolism—usually via copper's involvement in enzyme function. In fact, one of the major effects of copper deficiency may well be its effect on enzyme systems reducing productivity via alteration of enzymatic activity in the body. In a number of research studies, it has been clearly documented that a copper deficiency can have an effect on fertility. This has been evidenced by a reduction in first-service conception rates, altered embryonic survival (in situations of embryo transfer), and a reduction in overall pregnancy rates. The effect on fertility can range from a very limited effect to a very pronounced decrease in first-service conception and overall pregnancy rates. It is interesting to note that in a number of studies where copper deficiency has clearly been documented, there often is no impact on fertility or any other reproductive parameter. In addition to its effect on fertility, research has shown that there will be an alteration in reproductive behavior, or the manner in which cows show estrous activity. Specifically, cows may show normal estrous behavior and then in situations where a severe copper deficiency develops, ovulation does not occur and, subsequently, there is a retardation of future estrous cycles. In addition, there is evidence that copper can cause an alteration in semen quality in males. Exactly how does copper alter reproductive function in animals? Some excellent research showed that the effect on reproduction may not relate to a copper deficiency but rather may relate to the copper deficiency being created by excesses of other trace elements such as molybdenum and sulfur. Considerable attention in the livestock industry is focused on trace element deficiencies such as copper, selenium, zinc, and other elements. One of the hidden trace elements that may have considerably more influence than we realize is manganese. As with copper, manganese probably exerts its greatest influence on the animal via its effect on enzyme systems. Research evidence exists that manganese deficiencies can have an impact on suppression of conception rates, delayed estrus in both postpartum females and young prepubertal heifers. In addition, there is excellent evidence that manganese deficiency will cause abortions in animals and deformed calves at birth. There has been evidence that calves, at birth, will "knuckle over" at the fetlock. Other symptoms reported include poor calf growth and loss of hair color in both calves and cows, and an increase in the incidence of cystic ovaries. The mode of action by which manganese causes this deficiency is not clear other than it appears to be exerting these influences via enzyme systems in which it may be an essential cofactor. There is strong evidence, for example, that the manganese content of ovaries in normal cows was considerably higher than in those with high incidences of cystic ovaries. There is also excellent evidence that manganese, via its effect on enzymes systems, alters the synthesis of gonadal steroids such as estrogen and progesterone in the female. Part of this explanation relates to the role of manganese in altering ovarian luteal metabolism. Selenium, an important trace element in many areas of the United States, can be both deficient and toxic even within the same state. Any discussion of selenium also needs to include vitamin E. Although vitamin E will not be discussed to any extent in this article, there is excellent evidence that the role of vitamin E in beef cow diets needs to be reevaluated, and it is very likely that in the future we will be using higher levels of vitamin E supplementation in a beef cow diet. One manner in which a selenium deficiency can affect production in a cowherd is an increase in the incidence of early embryonic death. In addition, another common clinical symptom associated with selenium deficiency is an increase in the incidence of retained placentas with evidence in dairy herds of a selenium deficiency increasing incidence of retained placenta from a level of 8 to 10 percent to 50 percent. Another effect of a selenium deficiency associated with reproductive functions is an increased incidence of cystic ovaries and an increased incidence of weak or silent heat periods. Finally, evidence exists linking selenium deficiency to weak calves at calving time. Zinc, as with all trace elements, is actively involved in enzyme function. The role of zinc in reproductive function appears to be more pronounced on the male side than on the female side. Evidence exists in research studies that zinc deficiency in the bull causes impaired fertility, possibly associated with an alteration in the late-stage spermatozoa formation. This impairment of male fertility appears to be associated with the role of zinc as an activator of enzymes involved in the steroidogenesis process, which results in the secretion of testosterone and related hormones.

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