For producers considering Rumensin in heifer and mature cow rations for the first time, there are some points worth keeping in mind.

First, Rumensin is toxic to horses. That means not only keeping them away from mineral or feed mixed with the ionophore, but making sure horses don’t have a chance to come across residual amounts when swapping pens and pastures.

Secondly, Blasi explains folks trying to mix appropriate levels of the ionophore into feed on their own are kidding themselves. Rumensin is mixed at 80-90 grams/ton. You’d be hard-pressed to find a cow-calf producer with the necessarily sophisticated technology to mix it so precisely.

So, Blasi and Randel stress that the ionophore should be added to feeds and mineral by reputable commercial firms.

Next, if you haven’t fed an ionophore previously, Blasi says you need to understand that it will reduce mineral, forage and feed consumption.

Reduced mineral intake saves money, of course, but Blasi says it bothers producers who mistakenly equate mineral quality with the level of mineral consumption. He believes an added benefit of Rumensin in mineral is that it prevents over-consumption of mineral mixes, which he believes is a common problem.

Finally, the quality of feed available needs to be considered.

“If forage quality is too poor, you will reduce forage intake to the point that the effect of using the ionophore can be negative,” Randel says. “If forage quality is less than 6% crude protein and digestibility is around 45-50%, using an ionophore is probably counter-indicated.”

At the very least, the amount of ionophore fed should be adjusted with ration quality, Blasi says. The higher the forage quality, for example, the more Rumensin that can be fed and benefits returned (Table 1).

“There’s something to be said for keeping Rumensin in front of cows through the mineral year round,” Blasi says. If that’s done, he’s comfortable with a rate of 100 mg/day. “At 2¢/head/day, you’re talking $7/cow/year.”

In round numbers, Randel says, “If you use ionophores within reason (according to recommended dosage), you should see a net decrease of about 10% in the cost of feed to develop heifers to puberty and pregnancy... Where there is the opportunity for daily supplementation, I advocate the use of ionophores. It should improve your bottom line unless companies are charging too much for the ionophore.”

As for mature cows, in that 2011 OSU study, those receiving common prairie hay and 2.0 lbs./day of supplement (30% crude protein) with 200 mg/day of Rumensin gained 30 lbs., or about a half BCS over 58 days as mentioned previously.         

“There are a lot of places where producers can spend their money,” Blasi says. “I believe providing ionophores to growing cattle and mature breeding cows is one of those things that offers producers a definite return.”