Direct Effects of Complexed Trace Minerals on Reproduction

Research has shown that improving zinc status by feeding complexed zinc improves reproduction. Research conducted at the University of Tennessee (9) indicated that feeding an additional 800 mg of zinc (400 mg from Zinpro complexed zinc and 400 mg from zinc sulfate) to late gestation cows, which were already receiving a diet containing 100 ppm of zinc, resulted in better reproductive performance postcalving. Cows fed the additional zinc prepartum had fewer days to first estrus, less udder edema when cows were fed diets high in iron and tended to have fewer days to first service. Graham et al. (24) found that feeding additional zinc in the form of complexed zinc improved health status of dairy cows. Incidence of mastitis, stillborns, spontaneous abortions and lameness were reduced in cows supplemented with Zinpro complexed zinc (Table 2).

Table 2. Effect of Zinc Supplementation on Estimated Risk For Abortion and Other Disorders (24)

^a Cross product ratio indicating likelihood of having the problem
^b Control = methionine
^c ZINPRO^® zinc methionine

Spears (59) reported that beef cows supplemented with complexed zinc and manganese rather than zinc and manganese oxide had a 15.7% improvement in pregnancy rate when artificially inseminated (Table 3). At the end of the 80 day breeding period that included first, AI then natural bull service, there were 3.1% more cows pregnant in the Zinpro complexed zinc and manganese group than in the zinc and manganese oxide group. Spears noted that if the goal is to reduce days open and maintain maximum economic potential, then feeding more bioavailable trace mineral sources needs to be a management consideration (59).

Table 3. Effect of Zinc and Manganese Source on Pregnancy Rate of Cows Bred AI (59)

In another study at North Carolina State, replacing inorganic trace minerals with Zinpro complexes has been shown to improve uterine health (53). Feeding cows complexed zinc, copper and cobalt, both before and after calving reduced incidences of uterine infections by 54.2% (53).

A study conducted at the University of Tennessee indicates that feeding a combination of Zinpro complexed zinc, manganese, copper and cobalt three weeks precalving numerically reduced incidence of retained placentas by almost 38% (61). If the cows did retain the placenta, complexes supplemented precalving helped alleviate the negative effect retained placentas have on cows returning to normal ovarian function as evidenced in the reduction in days to first estrus, days to first luteal activity and days open (61). Similar results were observed in another study in which feeding complexes prior to calving reduced incidence of retained placentas, cystic ovaries and mastitis/metritis (49).

Research at the University of Tennessee also indicates that feeding a combination of Zinpro complexes in the postcalving period also helps alleviate the negative effects retained placentas have on reproduction (10). Small numeric responses on reproduction were observed when cows that did not retain the placenta were fed complexes. However, when placentas were retained, cows fed complexes showed estrus 37 days sooner, first luteal activity 11.8 days earlier and first corpus luteum 5.4 days earlier than cows that did not receive complexes (10). Overall, feeding Zinpro complexes reduced days to first estrus. Results from these studies indicate that cows fed complexed trace minerals were better able to respond to stress such as retained placentas, as evidenced by the quicker return to normal ovarian activity.

In a summary of 11 separate studies, feeding Zinpro complexes reduced days open by 23 days (Figure 1) and reduced services per conception by 0.3 services (2, 10, 35, 36, 37, 49, 62, 63). It should be noted that the control diets fed in most of these studies exceeded NRC requirements (46) for these trace minerals, in some cases by several-fold.