Do Antibiotics Really Make Animals Grow Faster?

If you read enough about today’s various “food movements,” you’re bound to run across articles about the use of antibiotics on farm animals.

Much of today’s meat production involves the use of antibiotics not merely to treat sick animals but as a preventative measure to prevent illness in the crowded and often messy conditions so many of our food animals live in these days.

Antibiotic Resistance

A surprisingly clever cartoon, and so conveniently related to my post. Courtesy, JAMA, March 9, 2001, Vol 305, No 10.

This raises the major concern that we’re encouraging antibiotic resistance.  This tends to happen when we use large quantities of antibiotics, because antibiotics tend to wipe out bacterial populations that are susceptible to antibiotics, leaving room for antibiotic-resistant bacterial strains to survive and propagate.  And if these antibiotic-resistant strains start infecting humans, there’s not much we can do about it.  Our antibiotics will no longer help us.

This much has always made sense to me.  Want to keep animals in cramped, nasty conditions?  You may have to feed them antibiotics to keep them alive.

But one element of antibiotic use on food animals never made sense to me: Inevitably, when people talk about antibiotic use on food animals, they claim that these antibiotics make the animals grow faster.  Not that the antibiotics help us to keep animals alive in conditions that otherwise help the animals grow faster (i.e., tight spaces where they can’t move and burn calories), but that the antibiotics themselves actually make the animals grow faster.

How could this be?  And could this be?

Apparently, it could.  Farmers seem to have started this practice (feeding antibiotics to animals to promote growth) several decades ago because they noticed that, sure enough, when they fed their animals antibiotics, the animals grew faster.  They didn’t know why, and they didn’t care.  What more reason did they need?

But recent studies suggest a possible answer.  Mice fed antibiotics in lab conditions grew faster, and gained more fat, than mice not fed antibiotics.  The scientists who conducted the study believe the cause is a change in gut bacteria.  For some reason, when antibiotics kill of selective gut bacteria and allow others to repopulate a mouse’s guts, it changes the way the mouse grows and stores fat.  Go figure.

Is this how it works in farm animals, too?  We’re really not sure.  Studies haven’t necessarily proven this connection (between antibiotics and animal growth) definitively, and we’re only making guesses at this stage as to why it works, assuming it does.

This is probably why all the articles you see out there say that the antibiotics “promote growth” but offer no explanation as to how or why.

But for those of you who were as confused as I was as to what, if any, connection antibiotics could have to weight gain, I thought I’d offer up this study’s one suggestion.  In any event, when articles suggest that antibiotics have this effect, you can assume there’s a good chance that they’re right.  Someday we’ll know why.

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