Trace mineral nutrition and its application in dairy rations continues to receive significant attention through research and its implementation in the field. Our nutrient requirement systems, such as the Dairy NRC, work well at predicting requirements for energy, metabolizable protein and other nutrients needed in comparatively larger quantities to support maintenance, growth, pregnancy and lactation in dairy cattle.
However, accounting for the nutrient requirements for many of the systems, for which trace mineral nutrition is critically important (examples of these would be immune function and oxidative metabolism), is very difficult.
Furthermore, accounting for the specific bioavailability at the farm level of dietary trace minerals is difficult because of numerous antagonisms that can affect the absorption of one or more trace minerals.
The dairy industry has access to multiple forms of trace minerals such as zinc, copper and manganese. Traditional inorganic sources consist of these metals bound via ionic bonds to sulfates or oxides; sulfates are more bioavailable than oxides.
Although there likely is variation in bioavailability among sulfate sources, I am not aware of any published information on the bioavailability of different sulfate sources.
Organic sources consist of these metals chelated, complexed or covalently bonded to amino acids, analogues of amino acids, proteins or organic acids such that they tend to be more bioavailable in the intestine.
Recently, hydroxy forms of trace minerals have become available for dairy (they have been available for many years for poultry and swine). These are inorganic sources but with covalent bonds that gives them greater bioavailability than sulfates.
Most research to date has explored either partial or full replacement of sulfates or oxides with organic sources or hydroxy sources of zinc, copper or manganese.
Although there certainly is variability in results from study to study, meta analysis of studies conducted in which organic trace minerals were fed suggest increased milk yield as well as improved reproductive performance.
Other commonly reported results from feeding organic sources of trace minerals include decreased somatic cell count and decreased lameness or improved hoof health.
One of the challenges at the farm level is that responses to more bioavailable trace minerals may be economically favorable, yet differences in performance, reproductive performance or health may be within the normal variation observed on the dairy and therefore nearly impossible to measure directly within the farm.
Thus, we need to rely in many cases on the body of research and consistency of the research to give confidence to the decision to feed more bioavailable forms of trace minerals.
We have conducted several studies in our research group over the past several years focused on various aspects of trace mineral nutrition and its effects on metabolism, immune function and performance.
In one study, we compared feeding either sulfate-based sources of zinc, copper and manganese with organic sources of these trace minerals at either NRC-recommended levels (about 50 ppm zinc, 10 ppm copper and 20 ppm manganese) or common commercial levels (about 70 ppm zinc, 18 ppm copper and 35 ppm manganese) in diets for lactating dairy cows.
Regardless of level, cows fed the organic sources had lower concentrations of plasma analytes related to oxidative stress. Furthermore, antioxidant activity was similar for cows fed the organic source at the lower level compared with cows fed either source at the higher levels in the diet, suggesting that feeding the organic source at a lower level in the diet was similar to feeding higher overall levels of trace minerals.
Recently, we compared feeding hydroxy forms of zinc, copper and manganese with either sulfate-based forms of these minerals or a blend of sulfate-based forms (75 percent) and organic forms (25 percent) to dairy cows during the transition period and early lactation.
Final total diet concentrations averaged about 80 ppm zinc, 16 ppm copper and 62 ppm manganese during the pre-calving period and about 100 ppm zinc, 22 ppm copper and 76 ppm manganese during the post-calving period.
Cows fed the hydroxy sources of trace minerals tended to have lower concentrations of plasma analytes related to oxidative stress and evidence of improved milk yield during early lactation compared to cows fed sulfates alone; performance and metabolism was similar between cows fed the hydroxy sources and the blend, except for a trend for lower concentrations of a marker of inflammation during week one post-calving in cows fed the hydroxy sources.
One other trace mineral that has received significant research attention in recent years is chromium. Chromium is available to feed to dairy cattle in the U.S. as chromium propionate with typical target feeding rates of 8 mg per day of chromium.
Most of the studies conducted during the past 15 years that have fed various forms of chromium to transition cows have reported increased milk yield during early lactation and increased dry matter intake during early lactation.
Some of the studies have also reported increased dry matter intake during the pre-calving period and decreased concentrations of NEFA in plasma during the transition period, suggesting favorable effects of chromium on energy metabolism.
There are also some indications that chromium supplementation may benefit reproduction. In a recent study in our group, cows fed chromium during the transition period and early lactation had decreased incidence of cytological (subclinical) endometritis during early lactation, which would indicate improved uterine health.
Further research needs to be done to more comprehensively evaluate potential effects of chromium on reproduction.
Take-home concepts and recommendations for the dairy nutritionist and dairy producer:
- Trace mineral nutrition doesnĂ˘ÂÂt fit traditional approaches for determining nutrient requirements very well; improved trace mineral nutrition results in subtle yet important changes in biological function that may impact performance, reproduction and health in a variety of ways.
- Feeding more bioavailable forms of trace minerals (especially zinc, copper and manganese) generally results in enhanced production, reproduction and health, although responses in the research vary.
- We really should be looking at total dietary concentrations of trace minerals. For dairy cows both during the dry period and early to mid-lactation, good ranges are 60 to 80 ppm of zinc, 15 to 20 ppm of copper and 40 to 60 ppm of manganese.
- Use of more bioavailable sources of trace minerals will typically allow nutritionists to target the lower ends of the ranges above. Although more research is needed in which more bioavailable forms are fed at lower levels in the diet, we may be able to continue to decrease total overall feeding levels with more bioavailable forms.
- Although still fairly new on the market, the research on chromium supplementation to transition cows suggests generally improved performance and metabolism along with potential benefits on reproduction.
For a more detailed review of trace mineral nutrition in dairy cattle, see Overton, T.R., and T. Yasui. 2014. Practical applications of trace minerals for dairy cattle. Journal of Animal Science. 92:416-426. PD
Professor of Dairy Management