For years, as scientists noted what appeared to be a link between increased stress in animals and increased instances of disease, supporters of humane livestock production have suggested a happy animal is a healthier animal. Now a team of researchers from the University of Bristol in the United Kingdom has discovered that high levels of a stress hormone in chickens actually increase the risk of Campylobacter infection.
Campylobacter is a foodborne bacteria that infects an estimated 2.4 million people each year and is one of the top causes of foodborne illness in the United States, according to the Centers for Disease Control and Prevention (CDC). The bacteria can live in the intestinal tract of even healthy birds, passing from bird to bird through common water sources or contact with feces. In humans, Campylobacter infection causes symptoms such as diarrhea, cramping, abdominal pain, nausea, vomiting, and fever within two to five days of exposure. The CDC estimates the bacteria kill approximately 124 people nationwide per year.
The British researchers initially surveyed nearly 800 broiler flocks in the United Kingdom and determined risk factors for infection. They found that the health and welfare of the chickens was a significant factor in the proliferation of Campylobacter. “If you compromise the host chicken, its ability to control the infection is also compromised,” says Tom Humphrey, lead researcher for the team who is now a professorial fellow in food safety at the University of Liverpool and science director for the National Centre for Zoonosis Research.
When the researchers isolated the stress hormone norepinephrine and began studying its effects in the laboratory, they found a series of disturbing results. The stress hormone caused rapid growth of Campylobacter and increased its virulence and gut permeability, giving the bacteria an easy way out of the gut and into the chicken meat. “The bacteria’s ability to affect the chicken is enhanced if the bird is in a stressful situation, and the bacteria is also more likely to infect muscle tissues,” Humphrey says.
Factory farmed chickens provide an ideal environment for the proliferation of Campylobacter. “You’ve got heat stress, rapid growth stress, ammonia stress due to poor air circulation, broken bones from rough handling,” says Temple Grandin, an expert in low-stress animal handling facilities and professor of animal science at Colorado State University. “There are huge differences between the chickens coming off well-managed farms [that show regard for the animals’ emotional well-being] and poorly managed farms.”
A few bacteria contained in the intestine may rarely come into contact with a consumer, whereas a stressed chicken will have an increased level of Campylobacter cells that have traveled into the surrounding meat, making the bacteria nearly unavoidable in our kitchens. The Food Safety and Inspection Service (a division of the U.S. Department of Agriculture) reports that the bacteria can be found in almost all raw poultry. Even one drop of juice from a raw chicken is enough to cause food poisoning in humans. According to the CDC, Campylobacter infection can be avoided by handling raw meat properly prior to cooking. Cook chicken until it reaches a minimum internal temperature of 165 degrees Fahrenheit, and thoroughly wash hands, utensils, countertops, and especially cutting boards to prevent cross-contamination of other foods.
“I started life as a butcher and have worked for 25 years on this,” says Humphrey. “For the industry to control the problem, they need help.” Humphrey and his fellow researchers are working with industry leaders to identify steps to reverse this alarming trend, including reducing stocking densities and controlling the humidity of the animals’ environments in order to reduce heat stress.
Both Humphrey and Grandin say management is key to raising healthy chickens that are safe to eat. “It’s not about feed, and a vaccine is not practical,” Humphrey says. “Better management is the path we must take. A happy chicken is a safe chicken. If [consumers are willing to] pay two or three pence [cents] more for a chicken, we can completely change these outcomes.”
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