The advantage of using antibiotics as a growth promotant in food animals has shrunk to a tiny margin, say two Princeton University researchers who surveyed recent papers on performance in hogs and poultry. From 1950 through 1985, studies showed decidedly higher daily weight gain with sub-therapeutic use of antimicrobials, from 4 percent in slaughter hogs to 16 percent in “starter” pigs. “However, for post-2000 studies, the literature suggests that productivity gains … are much lower than indicated by earlier research,” write Aude Teillant and Ramanan Laxminarayan in Choices, the agricultural economics magazine. There may be no significant response by finishing hogs and a small but significant response among nursery pigs to the growth promotants. Teillant and Laxminarayan say improved nutrition, hygiene, genetics and animal health make antibiotics less important for growth.
“If the benefits … have diminished, then it becomes reasonable to be cautious and avoid the potential public health costs,” they said. “The use of antibiotics should principally be the last resort rather than a substitute for biosecurity, hygiene and other good practices …. Since the new cases of antibiotics will likely not be available to veterinary medicine, it is in the best interests of food animal producers to preserve the effectiveness of existing veterinary antibiotics through antibiotic stewardship.”
Studies have produced differing estimates of ending the use of antibiotics to promote weight gain. Some see sizable decreases in net profits or high production costs. A World Health Organization valuation said there was a net increase in production costs of 1 percent when Denmark banned antibiotics as growth promotants. The USDA estimated in 2014 that hog and broiler chicken production might decrease by about 1 percent if antibiotics were not available to aid weight gain. But wholesale prices would rise enough to offset the additional costs.
The FDA is part-way through a three-year phaseout of medically important antibiotics as growth promotants for food animals. Antibiotics will remain available for treating and preventing disease and some classes of the antimicrobials will be available for sub-therapeutic use. Teillant and Laxminarayan say use of antibiotics for growth promotion “may be declining in the United States” anyway due to decisions by companies such as McDonald’s and Perdue Foods to curtail use of the drugs.