Cow herd mineral nutrition: Consider the source

Magnesium

As we speak, producers across the country are waving goodbye to winter and gratefully turning the cows out to spring pastures. Hopefully, you’ve already considered the importance of adding high magnesium to your mineral program prior to turnout in order to avoid grass tetany.

Stephanie L. Hansen

All that lush, rapidly growing grass is high in potassium, which prevents the cow from using the magnesium found in grass. Supplementing high-magnesium mineral for a few weeks prior to turnout, as well as through the first several weeks of the grazing season, should keep your cows’ blood magnesium high enough to prevent tetany.

Trace minerals

An analysis of forages across the major cow-calf producing states (USDA, 1996) suggested the majority of forages are marginal or deficient in copper, cobalt, selenium and zinc. Manganese tends to be higher in forages, though little is known about the availability of this manganese to the animal.

Cattle require several trace minerals to support optimum production. These include those offered in very small amounts (0.1 to 0.5 parts per million in the total diet) as well as:

Iodine – critical in temperature regulation and body energy metabolism
Cobalt – needed for rumen microbes to synthesize vitamin B12 for the cow to utilize dietary energy properly
Selenium – important in antioxidant enzymes, energy metabolism and prevention of retained placenta at calving. Be aware of all sources of selenium (i.e., enriched yeast, injectable, other dietary supplements), as there is a smaller margin of error with selenium between deficiency and toxicity.

There are additional trace minerals required in slightly higher amounts (10 to 50 parts per million in diet), including:

Copper – essential in antioxidant function, iron metabolism, energy metabolism and growth
Zinc – involved in dozens of biological pathways, including those impacting growth, reproduction and antioxidant status
Manganese – important in reproduction, antioxidant status and cartilage growth
Iron – critical in oxygen transport to tissues. Cattle almost never require additional iron supplementation, so there is no need to have extra iron in the mineral pack.

Antagonists

If your ranch truck tires are caked with red mud, your water source smells like rotten eggs, or you feed a lot of ethanol co-products, then you’re familiar with one of the biggest challenges in mineral nutrition – antagonists.

Antagonists are things found in the diet (or water) that decrease the ability of your cow to use many trace minerals. That red dirt is full of iron, which can prevent the absorption and use of manganese and copper, both important in reproduction.

And that rotten egg smell is hydrogen sulfide, a nose-curling symptom of high-sulfate water especially problematic for absorption of copper when combined with high-molybdenum forages (often found in Western states). While high levels of specific minerals can create challenges, utilizing mineral sources with differences in bioavailability can reduce the risk of deficiency due to antagonism.

Bioavailability

Have you ever stared at a mineral tag for several minutes wondering what the difference between an amino acid-complexed mineral and a sulfate or oxide was? You’re not alone. Advances in the production of minerals for cattle have brought the industry some exciting opportunities, but also a lot of confusion. Let’s start with this statement: Always consider the source.

Minerals are broadly lumped into two categories:

Inorganic – essentially sulfates, carbonates or oxides that have been mined from the earth or purified from the mining of other elements
Organic – minerals which have a ligand attached to them. In most cases, the ligand is an amino acid like glycine or methionine, or another molecule like propionate.

In many cases, inorganic minerals are able to meet the nutritional needs of the cow herd. However, if antagonists like iron, sulfur or molybdenum are a concern in your production system, you may want to consider feeding a proportion of your mineral in an organic form.

This may be particularly important at critical times in the production cycle, such as prior to calving and before re-breeding. It is almost never necessary to change your mineral to only organic sources; instead, look for mineral packs with both inorganic and organic sources listed.

Implementing a successful mineral program

Cows don’t know how to read (surprising, I know). As a result, they don’t eat free-choice mineral based on the label recommendations but rather based on palatability and availability. If you feed a 4-ounce mineral, you’ll feed a pound of mineral (16 ounces) per four cows.

Do the math and monitor how quickly the cows are going through free-choice mineral. Salt content should be somewhere between 10 and 20 percent to ensure a palatable source of mineral for cattle. The closer the feeder is to water, the greater mineral intake will be, and you can move the feeder farther from or closer to the water to alter intake.

Try to keep the feeder full of mineral, but also monitor intake. And don’t forget to account for curious calves finding the mineral feeder as well as the season progresses.