Q: I frequently read that monensin prevents bloat, but the research that I find suggests it prevents acidosis. Does monensin prevent bloat or founder? (November 15, 2010)
A: Following is the information found about the use of monensin in livestock feeding programs.
The data submitted in support of this NADA satisfy the requirements of section 512 of the Federal Food, Drug, and Cosmetic Act and 21 CFR Part 514 of the implementing regulations. The data demonstrate that monensin sodium fed at the rate of not less than 50 nor more than 200 mg per head per day in not less than one pound of Type C Medicated Feed; or after the 5th day, feed at the rate of 400 mg per head per day every other day in not less than 2 pounds of Type C Medicated Feed for increased rate of weight gain or fed at a rate to provide 0.14 to 0.42 mg per pound body weight per day depending upon severity of challenge up to a maximum of 200 mg per head per day for the prevention and control of coccidiosis due to Eimeria bovis and Eimeria zuernii in growing cattle on pasture or in dry lot (stocker and feeder cattle and dairy and beef replacement heifers) is safe and effective for the claims indicated in section 1 of this FOI Summary.
It has no claims to control bloat or founder. Monensin is approved for the claim of increased ADG. It does that by affecting one of the three volatile fatty acids produced in the rumen. Monensin increase the amount of propionic acid (not butyric or acetic acids). This has an impact on feed efficiency and therefore ADG. It also claims control and prevention of coccidiosis.
The feeding data in a feedlot indicates when monensin is included in the diet, there is a more consistent feed intake and hardly any swings in intake. This results in cattle not going off feed, cattle don't tend to over-eat therefore the chances of founder are almost eliminated, and if cattle don't over-eat, feedlot bloat is not a factor. So control of founder and bloat are not on the label, there appears, from the feedlot data, a secondary effect.
Dr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska - Lincoln, Lincoln, NE