Many factors contribute to rising feed costs: diet formulation, feed wastage, ingredient selection and purchasing. One frequently mentioned cost-cutting measure, because it is a direct cash cost, is to eliminate minerals and particularly trace mineral supplementation. However, all dairy diets need some supplementation as natural, home-raised feeds are usually low in most required trace minerals. Not supplementing will result in a moderate deficiency.
There will be no immediate decrease in milk production. Over time, however, reproductive performance will decline and more health problems will become evident. This leads to a higher cost than daily supplements.
Adequate trace mineral supplementation during the dry period is important for the health of cows at calving and in the subsequent lactation. Health disorders correlated with a suppressed immune system include mastitis, retained placenta, udder edema and increased susceptibility to infection.
In addition, the newborn calf’s immune system can be compromised if the dam is deficient in trace minerals. Newborns rely on the trace minerals received in utero and through consumption of colostrum.
The effects of moderate trace mineral deficiencies has been reported in a 2009 survey of French and Belgium beef and dairy herds. In cattle diets deficient in selenium, supplementing with selenium resulted in an increase in the amount of immunoglobulins in colostrum and higher calf serum immunoglobulin levels. In a 2006 survey by the same author, beef and dairy herds deficient in copper, zinc and selenium were identified as having a higher risk for one or more calf health disorders (perinatal mortality, diarrhea, vaccination failure and heart failure). The earlier survey also indicated that a selenium deficiency puts calves at greater risk for a health disorder than a copper or zinc deficiency.
No soil trace mineral analysis was done in either study. Yet one would suspect the response to selenium supplementation was best because this was a more acute deficiency; many soils are very deficient in selenium compared to more marginal deficiencies of copper or zinc. The 2006 survey also indicated that a copper deficiency did not affect the cow but that calf health was compromised, whereas a zinc deficiency was more likely to be observed in cow lameness and decreased milk production than calf scours.
Eliminating trace mineral supplementation during the dry period is not an economically correct decision. On the other hand, oversupplementation has not been shown to substantially benefit either cow or calf health.
Unless antagonists are suspected or soils are known to be very deficient or high in a particular trace mineral, the following supplementation of dry dairy cow diets should provide adequate trace minerals to meet the health needs of both the cow and calf at calving (mg/kg or ppm of the diet dry matter): cobalt–0.4; copper–15.0; iodine–0.6; manganese–50.0; selenium–0.30; zinc–60.0.