In discussions about mineral supplementation, it's good to remind your clients that the timing for correcting mineral deficiencies is critical.

Since many of these problems manifest in calves and begin in utero, the fast-growth third trimester is a critical time to be certain cows are full-up on supplements, says Dr. Jeffery Hall, toxicology lab manager for the Utah Veterinary Diagnostic Laboratory.

With copper, selenium and zinc in particular, calves need to be born with ample supplies -- actually higher normal ranges than in adult cattle. There are two reasons they need such large stores at birth: First, they can triple their birth weight in the first 60-90 days, thereby diluting their body stores from birth. Second, concentrations of these minerals in milk are very low, while at the same time a young calf is getting a major portion of its nutrition from milk.

The normal process is the cow moves these and other nutrients to the fetus during gestation. If there is a deficiency in the young calf it is because the cow had a deficiency. That can be caused by actual deficiency of these minerals in the diet, or it can result from interference by high levels of such minerals as iron, sulfur, selenium or molybdenum.

Speaking of that, mineral interference is another thing to warn them about, Dr. Hall says.

He tells a story about a beef producer who heard him speak about mineral deficiencies, tested his cattle, and learned they were severely deficient in copper. The operator decided to save money by just feeding copper sulfate and salt.

Dr. Hall says this operation lost 8-9% of his calf crop the first year, mostly from copper deficiency. The next year he lost about 10% of his calves, but this time because of a selenium deficiency caused by the excessive copper he had been feeding. This is why Dr. Hall strongly recommends a "balanced" mineral product with appropriate mineral to mineral ratios.

Next article: Liver biopsies are the only viable way to measure copper deficiency, but never fear.