Part II by John Paterson, MSU Extension Beef Specialist

This month's column was originally aimed at the effects of trace mineral supplementation on reproduction and immunity of beef cattle. However, several readers requested that I discuss other trace minerals that might be deficient or even excessive in Montana forages and water. (Last month's column emphasized copper and zinc.) Why should I be interested in supplementing minerals to my cow herd? Minerals play a vital role in forage digestion, reproductive performance, the immune system and the development of bones, muscle and teeth. An inadequate intake of minerals and vitamins may result in 1) reduced forage intake; 2) lower reproductive efficiency; 3) poor disease immunity; 4) slower daily gains and 5) poorer feed conversion. Sub clinical trace mineral deficiencies occur more frequently than recognized by most livestock producers. This may be a larger problem than an acute mineral deficiency, because the rancher does not see specific symptoms that are characteristic of a trace mineral deficiency. With a sub clinical deficiency, the animal grows or reproduces at a reduced rate, uses feed less efficiently and operates with a depressed immune system. Texas A&M researchers believe trace element deficiencies may impact production in better-managed herds even more than previously recognized. Table 1 shows the six macro-minerals and seven trace minerals that cattle require.

Table 1: from ADM Nutrition Beef

Table 2 summarizes the observed symptoms of manganese, iodine, iron and selenium deficiences.

Troubleshooting a potential trace mineral deficiency

Step One--Other Factors: The first step in identifying trace mineral deficiencies is to attempt to rule out other more directly contributing factors to decreases in animal performance. For instance, if average cow body condition scores are below a five (moderate), chances are far greater that decreases in reproductive performance and/or immune competence are a result of energy/protein deficiency rather than a trace mineral deficiency. Secondly, be sure that proper management of free-choice trace mineral feeding is offered. For instance, are the cattle being offered a continuous supply of fresh, dry mineral? Are they consuming the mineral at the recommended level?

Step Two--Forage and Water Trace Mineral Concentrations.

Know the trace mineral contribution of the available feedstuffs. Collect forage samples, being careful to select forage that the animals are actually grazing or consuming as hay. Perform a standard trace mineral evaluation of the forage. Because of the ongoing drought in Montana, I would also suggest an analysis of livestock drinking water. The sulfate can play an antagonist role in both copper and selenium availability. Excessive levels of iron may also depress the utilization of copper. Your local feed representative or Extension agent can help you with forage and water sampling. A complete protein, energy and mineral analysis of your forage or water will cost between $25 to $30/sample.

Step 3--Herd Trace Mineral Status: In some instances it may be important to confirm or disprove a potential trace mineral deficiency by examining trace mineral status through blood and (or) liver collection. Liver samples provide the most reliable indicator of actual animal stores of copper and selenium.This is a fairly expensive option (~$40/sample) because of the number of samples required. Consider this option carefully before proceeding. If you suspect a potential mineral deficiency, please contact your feed company nutritionist, local veterinarian, Extension agent or beef cattle specialist