David L. Morris: Vet Column 12-27-10
Investigators from the University of Wisconsin recently published results of an experiment involving the use of organic trace mineral (zinc (Zn), copper (Cu), manganese (Mn), and cobalt (Co)) supplementation on reproductive measures in lactating dairy cows. Trace minerals that bound to organic compounds have been shown to be more readily absorbed from the digestive tract and may be more biologically available compared with the inorganic salts of these minerals.
Previous studies have provided data to support the fact that use of these four organic trace minerals in lactating dairy cow diets have resulted in increased milk production. Their effect on reproductive performance, however, has not been as predictable. The purpose of this recent study was to determine the effect of replacing a portion of the trace minerals with organic forms on milk production and reproductive performance.
For this study, 53 lactating Holstein and 10 Holstein/Jersey cows, including first lactation and older, were used. Cows were assigned at dry-off to receive inorganic trace mineral supplementation as controls (32 head) or to have a portion of supplemental inorganic Zn, Cu, Mn, and Co replaced with an equivalent amount of the organic forms of these minerals (31 head). Organic forms of these four trace minerals were substituted for inorganic forms in the treatment dry cow ration at the rate of 40 percent Zn, 26 percent Mn, 70 percent Cu, and 100 percent Co and in the lactating ration at the rate of 22 percent Zn, 14 percent Mn, 40 percent Cu, and 100 percent Co.
Overall milk production in this study was not affected by the substitution of organic forms at the rate included for inorganic forms. On a weekly basis, however, milk production increased at weeks 13 and 14 of the study. Compared to other studies, the majority indicated a positive effect for milk production when using organic forms of these trace minerals. This report suggests that supplementation of organic trace minerals may require a certain amount of time before the resulting biological effects are observed. In one study where a comparison was made over two sequential lactations of organic trace minerals with inorganic trace minerals at the same level, cows fed the organic trace minerals demonstrated increased milk production with the increase occurring earlier in the second lactation.
With regard to reproductive performance in this study, use of substituting organic trace minerals for inorganic forms did not affect health events, ovarian activity, embryo quality, or liver trace mineral concentrations.
Although cows in this study were fed a trace mineral source that was more biologically available, control cows were fed inorganic levels that met National Research Council (2001) (NRC) recommendations. It is also worth noting that estrous synchronization was used in this study to facilitate artificial insemination and subsequent flushing. As a consequence, the lack of reproductive improvement may have been countered with the use of hormone treatments.
In summary, use of organic trace mineral forms in dairy cattle rations can be beneficial to dairy producers in terms of increased milk production. Depending upon the reproductive program in use, reproductive benefits are less predictable, but not detrimental. The amount used and the duration of use are additional considerations when assessing benefit:cost.