Antibiotic Soup: M is for Monensin

There are antibiotics in our cattle feed.  I didn’t always know this.  But over the past several years we have been using monensin to feed the cattle.  When I heard all the fuss about overuse of antibiotics in the meat industry, I couldn’t believe it.  We rarely have to use penicillin or other injectable antimicrobials for sick animals.  For the most part I thought that we were raising our cattle without antibiotics.  But then I found out that monensin, an ionophore, is classified as an antibiotic.  I was really taken aback by this.  I had learned about ionophores in college.  I knew that they were feed additives used in cattle to increase feed efficiency and rate of gain.  What I did not realize until very recently was the mechanism by which they function gives them antibiotic properties.  Researchers discovered that monensin was effective in killing coccidiosis.

From Wikipedia:  Coccidiosis is the disease caused by coccidian infection.  It is a parasitic disease of the intestinal tract of animals, caused by coccidian protozoa.  The disease spreads from one animal to another by contact with infected feces or ingestion of infected tissue.  Diarrhea, which may become bloody in severe cases, is the primary symptom.  Most animals infected with coccidia are asymptomatic; however, young or immuno-compromised animals may suffer severe symptoms, including death.

Feedyards began using monensin to fight off that particular bacteria (Benefit #1) and then began noticing a side effect—a positive one.  Monensin caused increased feed efficiency (Benefit #2) and improved average daily gain (Benefit #3) of the animals in feedlots.  So from there researchers went about deciphering why and how this was happening. 

livestockandenvironment.org

Ionophores work on the volatile fatty acids (VFAs) that are in a cow’s rumen.  Acetic, butyric and propionic acids formed in the rumen provide greater than 70% of the ruminant’s energy supply.  Propionate is commonly known as the best VFA for cattle to change into glucose; propionate has the highest ability to be utilized from feed energy.  Ionophores increase the production of propionate and decrease acetate which in turn decreases the amount of methane produced from that animal (Benefit #4). 

To animal scientists and cattle producers this looked like a win-win situation.  Many cattlemen began adding monensin to their feed rations.  And they saw results.  They saw marked differences in condition and “bloom” of their cattle when comparing the animals before and after ionophore usage.  Cattle were healthier, average daily gains increased and feed efficiency was up.  So what is so bad about using antibiotics in cattle feed?

According to many people, they fear antibiotic overuse, resistance and “superbugs.”  I found a really good article from PBS.org (see Antibiotic Debate Overview) that discussed both sides of this issue with further links to information on antimicrobial resistance.  What the health experts are saying is trifold:  1) Antibiotic resistance is far reaching and largely due to universal overuse of antibiotics; 2) Any drug-resistant organisms that are present in meat are killed when the meat is cooked properly; and 3) While there are problems and concerns within the meat industry of antibiotic use, there is sound science being practiced to protect human and animal health.

Superbug – usc.edu

Other important points are:  Coccidia have been found to be species specific–so even if there are surviving organisms in meat, they are extremely unlikely to affect humans, especially after proper cooking; the class of antibiotics known as ionophores are not used for the treatment or prevention of disease (bacterial or otherwise) in humans; monensin is not related by structure or mode of action to any antibiotic used in human medicine; there is no withholding period for meat or milk from cows fed monensin; it has been determined that milk and meat from monensin-fed cows are safe for human consumption; and feeding monensin does not result in residues in meat or milk above levels considered to be negligible by FDA.

Well, it may be disconcerting to hear that there are indeed antibiotics in our cattle feed.  (It was to me at first.)  But I hope that this information has left you with a sense of relief that the ionophore monensin will not be a contributing factor in the battle against antibiotic resistance.

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