COLUMBIA, Mo. – With high costs of feed for wintering cows, herd owners should consider adding monensin to grain supplements for winter forages. The additive, trade name Rumensin, controls coccidiosis, a disease caused by intestinal parasites.

The additive improves beef-cow feed efficiency 10 to 15 percent, says Justin Sexten, University of Missouri Extension beef nutritionist.

“That’s like feeding hay for 90 cows to 100 cows,” Sexten says. “It improves digestion of poor hay. Adding Rumensin to grain fed to cows on winter hay makes economic sense.”

Recommended rate for beef cows is 200 milligrams per head per day, mixed into one pound of grain. Monensin must be fed every day, according to label.

Monensin, an ionophore, reduces cases of coccidiosis in beef herds. The disease results from a common internal parasite. While coccidiosis may not show symptoms in cows, it can be deadly to weaned calves.

In addition to disease control, ionophores change the microbial mix in the cow’s rumen, which digests forages. The microbial change also cuts methane production. Carbons in methane are digested rather than emitted as gas.

“For an easy way to use the supplement, ask your feed dealer to mix it with a grain ration,” Sexten says. “It gives a low-cost gain in feed efficiency. A daily dose costs about 1.8 cents. After adding mixing cost, the treatment costs about 2.5 cents a day.

“I encourage you to think about this,” Sexten told farmers at the MU Wurdack Farm field day.

He added a caution: Grain with monensin should not be fed to horses, which do not have a rumen. It can be fatal to equines.