why the chickens you eat take antibiotics -- 5/16/18

Today's selection -- from Big Chicken by Maryn McKenna. In 1948, Dr. Thomas Jukes was a researcher trying to identify which vitamins had to be added to chicken feed to allow birds to thrive on a manufactured diet:

"Jukes was ... interested in what chickens needed to eat in order to thrive in confinement -- and by an accident of history, that question was even more important than it had been 15 years ear­lier. World War II had spurred such demand for protein that production of chicken almost tripled, rising to more than one billion pounds of chicken meat per year. But when the war ended, the poultry market that it had guaranteed collapsed. Producers, forced to cope with more chickens than they had demand for, struggled to cut their costs. En masse, they switched their birds' diet from vitamin-rich fishmeal -- ground-up anchovies netted off the southern California coast -- to much cheaper soybeans. Chick­ens did not do well on soybeans, though. They grew slowly, and the eggs that hens laid were thin-shelled and did not hatch. Even when vitamins were added into their feed, as Jukes had learned to do in his first job, the birds did not thrive. People talked about needing to add a nutritious boost, an 'animal protein factor.'

Thomas H. Jukes

"Then Merck & Company, a Lederle rival, announced its researchers had found it. Merck was making streptomycin, ... brewing it out of Streptomyces griseus, the bacterium he had harvested from the manured patch of soil near the Rutgers University campus. Merck researchers said that a by-product of the brewing process made chickens do better, even when they were fed the low amounts of protein now present in conventional feed. Earlier in the century, researchers had identified and learned how to synthesize vitamins: B2 B3, B5, B6. Merck's scientists identified their new compound as the last in that series: vitamin B12.

"Jukes wondered if Lederle's own bacterium -- Streptomyces aureofaciens, the source of Aureomycin and a distant relative of the species the Merck scientists used -- could perform the same trick. That was what brought him to his office on Christmas morning, on a mild, dry day with just a dusting of snow. A few weeks earlier, he had set up an experiment to test whether Lederle possessed an animal protein factor of its own. Today he would find out. ...

"Christmas Day was the 25th day since the chicks had hatched, the point where Jukes had determined he would weigh them and assess the experiment. ...

A commercial chicken house with open sides raising broiler pullets for meat

"Then he moved to the pens containing the chicks that had been given the antibiotic discards. He had dosed them at four different levels, so much mash per kilo of feed. He weighed the four groups, averaged the weights within each of them, recorded the numbers, and looked. And then looked again. The birds that had gotten the highest dose of Aureomycin were the heaviest in the room. They weighed 277 grams, almost 10 ounces: two and a half times the control chicks' weight, a third more than the chicks receiving Merck's B12, and a quarter more than the chicks receiving the liver extract, an expensive ingredient that no farmer could afford.

"The chicks had gotten to that weight with the help of 60 grams of the mash containing a trace amount of Aureomycin. Sixty grams is two ounces, and two ounces is nothing: a handful of pennies, two slices of bread, an egg. Yet that tiny weight would exert enough force to alter the entire structure of agriculture -- and affect land use, labor relations, international trade, animal welfare, and the diet of most of the world."

 | www.delanceyplace.com


Maryn McKenna


Big Chicken


National Geographic


Copyright 2017 Maryn McKenna


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