As Michael Pollan discusses in his article in yesterday's New York Times, the rampant use of antibiotics in America's factory farms threatens to undermine its own efficacy. But why are antibiotics such a crucial piece of the industrial agriculture puzzle? Part of the reason is to fight off infections that tend to afflict animals confined to small spaces.
But that's not the whole story, at least with regard to ruminants (cattle, sheep, goats). In these livestock antibiotics are also used to fight infections that arise from abnormally high levels of E. coli, which in turn is a side-effect of the grain-based diet so common on factory farms. I was curious about this other side of antibiotics, so I asked a veterinarian friend of mine for some clarification.
I learned that E. coli is not inherently good or evil; there are trillions of them living happily my gut as I sit and type this. However, certain strains of E. coli (such as O157:H7, the strain made famous in the spinach outbreak of '06) create toxins that cause food poisoning in the human intestine. O157:H7 also has the added feature of being somewhat acid-resistant, and so can happily survive the low pH environment in our stomachs.
How does this connect to grain-fed cattle? Grain is rich in carbohydrates, and when it enters the rumen (the first of four stomach chambers of ruminants), the carbohydrate-digesting bacteria living there go to town, eating and multiplying like crazy. The by-product of this eating orgy is lactic acid, an accumulation of which serves to lower the pH considerably. This acid environment kills most of the rumen's beneficial microflora, which otherwise would help stave off the harmful E. coli. And of course since O157:H7 thrives in acid environments, it is unaffected by this pH change. Grass and hay, on the other hand, have higher protein-to-carbohydrate ratios, and so promote healthful bacterial growth in the stomach by maintaining a higher pH.
So how does this lead to increased use of antibiotics? Ruminal acidosis, as this ailment is called, leads to breakdown of the rumen wall, which in turn allows bacteria to travel from the gut into the bloodstream. The first stop for these bacteria is the liver, and so rumen acidosis can lead to liver abscesses. Antibiotics are used to treat problems such as these.
Ultimately, then, what follows from Pollan's argument about sustainability and antibiotic use is that sustainable livestock production must demand that the animals be fed mostly grass, hay, and silage. The flip side of this, however, is that we probably can't sustain our levels of meat consumption if the entire industry switched to grass from grain. There's simply not enough pasture to go around.
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