There is increasing evidence that farm animal stress can have a significant detrimental effect on food safety according to a recent study.

Though it is known that animal stress can lessen the quality of food products, and there is an assumption that there is a link between stress and food safety, very little is known about exactly how this interaction occurs.

Marcos H. Rostagno, an animal scientist at the U.S. Department of Agriculture (USDA), recently published the review titled, “Can Stress in Farm Animals Increase Food Safety Risk” in last month’s edition of Foodborne Pathogens and Disease to shed light on this issue.

Rostagno looked at the impact of stress on farm animals and the resulting food safety risk for pathogens like E. coli O157:H7, Salmonella, and Campylobacter. As the review points out, the dissemination of these pathogens into the food chain is “a major public health concern and economic concern for industries.”

As Rostagno acknowledges, all farm animals will experience some level of stress in their lifetime. Stress can result from a variety of factors including overcrowding, handling, heat, cold, and transport–transporting and unloading animals can have “substantial detrimental effects to their well-being” from causing stress.

There are a couple ways stress on the farm can translate into increased food safety risk.

First, stress can affect the health of the animal’s gastrointestinal tract. Brain-gut interaction can lead to stress-related gastrointestinal alterations and there is evidence that this interaction can disorders and infections.

Stress can cause the pH balance in an animal’s stomach to increase, which in turn increases the probability that foodborne pathogens like E. coli, Salmonella, and Campylobacter will survive gastric passage and colonize the gastrointestinal tract.

Stress can also increases animal susceptibility to new and more severe infections.

Recent studies have shown that “a substantial number” of pigs, cattle, and poultry are constantly carrying foodborne pathogens into slaughterhouses. Animals that carry pathogens in their gut provide a vehicle for spreading disease onto carcasses and into the food supply chain.

Not surprisingly, previous studies have found that the increased incidence of pathogens results in an increased incidence of carcass contamination, a dangerous correlation for meat producers and consumers alike.

In response to his findings, Rostagno recommends that more research be done on the relationship between stress and pathogen prevalence.

“It is imperative that the issue receives more research attention in the interests of optimizing animal welfare and minimizing losses tin product yield and quality, as well as food safety risks to consumers.”

Rostagno emphasizes the importance of such research for improving food safety and animal welfare practices. For example, Rostagno points out that if we knew when pathogen frequency and load on the farm are highest and we knew when animals are susceptible to infection, prevention and control measures could be adopted accordingly.

Additionally, more research could help change animal handling practices to minimize stress and food safety risk according to Rostagno.

Jim Marsden, a distinguished professor of animal sciences at Kansas State University, and leading food safety expert, agrees

“I am in full agreement that there is relationship between stress and the shedding of foodborne pathogens. Great care should be taken to prevent stress during the transportation and handling of food animals. Several feedlots and animal processing facilities have gone to great lengths to reduce stress,” said Marsden. “I see this as an important component of a pre-harvest food safety system.”