The deficiency of trace minerals in forages and the antagonistic effects of other minerals from drinking water are among the factors that add to stress in beef cattle. Ranchers should look closely at their trace mineral program and the effect of trace minerals on their herds' fnutritional status.
In general, trace minerals are required for vitamin synthesis, hormone production and the processes related to growth and health. Deficiencies usually occur either because animals don't consume enough of a trace mineral or because absorption of the trace mineral is inhibited by a dietary antagonist such as an excess of sulfate, molybdenum or iron.
Texas A&M researchers believe trace element deficiencies may impact production in better-managed herds even more than previously recognized. In fact, subclinical trace mineral deficiencies in cattle may be a larger problem than an acute deficiency. This is because subclinical symptoms aren't obvious and the deficiency — which could hurt gain efficiency or depress immunity — may go unrecognized.
With the exception of phosphorus (P), copper (Cu) and zinc (Zn) are the most deficient trace minerals in grazing beef cattle diets. There are indications that during stress, excretion of Zn from the body can double and Cu excretion quadruple.
Forage samples collected from three states suggest very noticeable and consistent deficiencies. Forage surveys show that Texas native grasses can be deficient in P, magnesium (Mg), Cu, manganese (Mn) and Zn for lactating cows. Montana hay samples have been short on Cu and Zn. Arkansas data on mixed-grass hays indicate that P, Cu and Zn are deficient only in certain areas.
Regarding livestock water quality, Canadian researchers found cows consuming high-sulfate water had lower concentrations of liver Cu compared to cows consuming low sulfate water.
Importance Of Zinc
Weaned calves normally experience stress due to transportation, changes in feed and handling. All these increase susceptibility to infectious diseases. During this period of stress, providing adequate dietary Zn may be critical.
Infection also can have a detrimental effect on Zn-status in cattle. One important note: The addition of Zn to diets has been shown to positively impact immunity in growing and finishing cattle.
Tests show that challenging cattle with infectious bovine rhinotracheitis (IBR) increased urinary Zn excretion, which caused a negative balance in the body. In addition, feed intake is often depressed with stressed feeder cattle and the reduction in intake results in a decrease of trace minerals ingested.
Supplying Zn to weaning- and transportation-stressed steer calves increased feed intake in a University of North Carolina experiment. Meanwhile, Texas A&M scientists found that dietary Zn enhanced the recovery rate of IBR-stressed cattle.
At Montana State University, we're investigating the effects of additional Cu, Zn, Mg, protein, vitamins A and E and a coccidiostat to calves for 28 days after weaning to evaluate the effects on feedlot morbidity. First-year results of this two-year, seven-ranch study found that calf morbidity fell when calves were backgrounded for 45 days versus less than 45 days (6% vs. 21%).
Although not statistically significant, calves fed additional levels of trace minerals, vitamins and a coccidiostat during the first 28 days of the 45-day program numerically had lower morbidities from weaning until harvest (6%) compared to control calves (20%). The morbidity range was 0-100% for control calves compared to 0.5-21% for treatment calves.
The reasons for not measuring a statistical significance are still unclear, but may be related to vaccination strategy, prior nutritional status and environmental effects.
Cow/calf producers should analyze their forages and water to see if supplemental trace minerals are needed or if antagonistic minerals are present at levels sufficient to reduce performance. In some areas, I've also recommended that weaned calves receive a well-balanced mineral supplement at least 45 days prior to weaning as one approach to help reduce morbidity.
John Paterson is an Extension beef specialist at Montana State University in Bozeman.