Ask the Vet

By Dr. Ken McMillan
DTN/The Progressive Farmer Contributing Editor

QUESTION: When I give minerals to my cows, the bags all have the same ingredients but in different percentages. How do I know what percentage of what mineral cows need? Also, if your soil analysis is high in one mineral, does this affect how much cows need of that mineral?

ANSWER: This is a topic we could discuss for hours. Certainly your soil analysis and the area of the country in which you live can have a huge impact on the minerals and amounts of each that need to be supplemented. Also, time of year and life stage should be taken into consideration.

The amount of minerals in forages varies tremendously over the year. Lower levels and availability of calcium and magnesium in lush spring grasses, combined with a cow's peak need for calcium and magnesium, may mean an increase in cases of milk fever (low calcium), grass tetany (low magnesium) or a combination of both (what I call lactation tetany).

The amount of minerals in the soil varies greatly across the country, which can create health problems. Selenium is a good example of something to watch.

If cattle receive too much selenium in supplements or feeds, and there's a high level of it in soils, it can become toxic. But in selenium deficient areas, inadequate supplementation can also cause health problems.

Because of these factors, there are many different formulations of minerals in widely varying percentages. What a company promotes for use in your operation and area may be based on how that company interprets research data, time of year, or life stage of the cow. In addition, interactions between minerals must be considered. When one is increased, the availability of another may decrease.

So what is the bottom line? First, a complete and balanced loose mineral should be available to cattle year-round in a weatherproof feeder. The needed macrominerals (those expressed in percentages) should include calcium, phosphorus, magnesium, sodium and chlorine.

Micronutrients (those expressed in parts per million or ppm) should include zinc, copper, iodine, selenium, manganese and cobalt. Other minerals may be needed in certain areas.

Find a brand and company you trust and stick with them. Then be sure cattle are consuming adequate amounts, generally 2 to 4 ounces per head daily. For a 25-cow herd, a 50-pound bag should last eight to 16 days.

(VM/AG)

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