Fine Tuning Mineral Management for Beef Cattle
By Dennis B. Herd, Ph.D., professor and Extension beef specialist-nutrition

Mother cows frequently don’t consume enough mineral supplement. Although composition of the mineral supplement is important, lack of intake limits performance more often than improper composition.

The recommended composition for mineral supplements for several forage types are given in Texas Cooperative Extension publication B-6056, “Mineral Supplements for Beef Cows in Texas.” This publication is a good place to start evaluating your mineral program.

It’s frustrating to evaluate the mineral adequacy of grazing cattle. Free-choice mineral consumption is variable and often nonexistent. When a protein-energy supplement is being fed, supplemental minerals are best added to the protein-energy supplement to make intake less variable and easier to manage. Cattle commonly quit eating mineral supplements entirely when protein-energy supplements are fed, especially when limited with salt.

Good pasture and hay seldom require protein-energy supplementation. The only way to get all needed minerals into the cattle is to provide a mineral supplement free-choice in a mineral feeder. Although complete mineral supplements can be purchased in block form for feeding on the ground, consumption is often inadequate.

Cattle need mineral year round, but it’s especially critical mineral intake is adequate during the last 90 days of pregnancy and on through the breeding season. Minerals have an important role in fetal development, colostral quality, newborn calf vigor, immune function in cattle of all ages and rebreeding of the cow.

Thus, it seems reasonable to make sure mineral consumption is plentiful (two to six ounces), but not excessive, for three months before and after calving. Then, continue to supplement during the rest of the year, but don’t allow "luxury" consumption, thus conserving mineral and money. Adequate body stores of minerals will carry cattle through times of insufficient intake, but this shouldn’t occur during critical times in the production cycle.

Add something they like to the mineral mix to encourage consumption. Protein supplements like cottonseed meal and soybean meal, ground corn, wet or dry molasses or commercial salt and meal protein supplements can be added to get adequate consumption.

Add five to 10 percent to the mineral and increase as needed to obtain the desired intake. Commercial manufacturers use particle size, prilling, coatings, oils, byproduct feed additives, flavoring agents, etc. to manage mineral consumption, but none of these techniques seem to work well in all situations, thus the need for additional management by cattlemen.

Here are some points cattlemen should be aware of regarding minerals.

Molasses Supplements Depress Copper Status
Two Florida studies by J.D. Arthington (Journal of Animal Science Volume 80:2787, 2002 and Volume 81:1357, 2003) documented molasses-based supplements deplete liver copper stores in cattle.

In one study, molasses supplements depressed copper status while corn supplements did not. Molasses is normally high in sulfur (0.5 to 1.0 percent). Excessive sulfur can reduce copper absorption and increase copper excretion, thus decreasing copper status of cattle. Organic sources of copper were no better than copper sulfate in maintaining copper status in these studies.

Is the depressive effect of molasses on copper status of practical importance? Possibly not, if the supplement is only consumed for two or three months a year since copper stores may be sufficiently increased while not consuming molasses to carry cattle through a short depletion period.

If consuming molasses supplements essentially year-round, the supplement should contain enough copper to ensure the total diet contains more than 10 ppm (parts per million) of copper on a dry matter basis (even more if known copper antagonists are also present in forage).

Use Sulfur-Containing Fertilizers Wisely
Adequate sulfur is required for synthesis of sulfur-containing amino acids, which serve as building blocks for forage protein. Excessive sulfur, however, can depress the copper status of grazing cattle.

Hardt et.al. (Journal of Animal Science 69:2310, 1991) reported two applications of ammonium sulfate (supplying 95 pounds of sulfur per application) to winter wheat/oat pastures near Beeville increased plant sulfur levels from 0.3 percent in control pastures to 0.5 to 0.7 percent in pastures receiving sulfur.

Levels of sulfur around 0.2 percent are considered adequate for cattle, and 0.4 percent is considered toxic though no signs of toxicity are commonly observed in grazing cattle. However, Arthington et.al. (Journal of Animal Science 80:2507, 2002) documented 67 pounds of sulfur per acre from ammonium sulfate increased sulfur levels in bahiagrass to 0.5 percent, as opposed to 0.22 to 0.25 percent in pastures not receiving sulfur and decreased liver copper status of cattle.

Though not statistically significant, cattle grazing high-sulfur forage gained five percent slower in the Hardt study and 15 percent slower in the Arthington Florida study.

So, what’s the point? A person needs to know copper and sulfur status of soil and forage before using a fertilizer containing sulfur. Excessive sulfur would be expected to be more detrimental to cattle performance if copper status in the feed and animal are low and other copper antagonists in forage (such as molybdenum, >2.5 ppm, and iron, >300 ppm) are high.

Adequate sulfur is required for plant growth and digestibility. Plants low in sulfur are often less digestible.

With sulfur, use a rifle approach, not a shotgun! Analyze soil and forage to determine sulfur levels. If they are low, fertilize with sulfur. However, if they are adequate to high, you best not overdo it or cattle performance in the areas of health, fertility, feed intake, digestion, and growth may be depressed.