Dairy farms are a reservoir of foodborne pathogens such as Salmonella, Campylobacter, Listeria, Staphylococcus aureus, and Shiga toxin-producing Escherichia coli. The process of preventing these pathogens from entering the food supply starts with you.

Where they reside

In order to reduce this contamination, you must first understand the pathogens you are battling. Many foodborne pathogens inhabit the intestinal tract of ruminants, and cows probably get infected through the consumption of water and feedstuffs contaminated with feces and other cattle secretions/excretions. Once pathogens start to grow in the cows, they are excreted into the dairy farm environment.

Foodborne pathogens in bulk tank milk are directly linked to fecal contamination that occurs primarily during milking. In addition, some foodborne pathogens can cause mastitis, which results in the pathogen being excreted in the milk. The final outcome of this cycle is a self-maintained reservoir of foodborne pathogens that can reach the human population by direct contact, ingestion of raw contaminated milk or cheese made with raw milk, or contamination during the processing of food. (Please see the diagram below.)

Especially important is the use of manure as a fertilizer or contaminated water to irrigate field crops. Contaminated manure and irrigation water have been probable vehicles for foodborne pathogen transmission in some human disease outbreaks. For example, E. coli O157:H7 was isolated on vegetables grown in soil fertilized with contaminated bovine manure compost or treated with contaminated irrigation water. This pathogen persisted in the soil for more than five months after application of the contaminated compost or irrigation water.  

Public health implications

Pasteurization is regarded as an effective method to eliminate foodborne pathogens and other bacteria from milk. However, the increasing number of incidences in which foodborne pathogens are detected in pasteurized fluid milk and ready-to-eat dairy products clearly indicate that pasteurization is not the ultimate tool to eliminate all foodborne pathogens.

In addition, consumption of raw milk has been recognized as a major cause of foodborne diseases. Yet, in spite of this, there appears to be increasing consumer interest in consuming raw milk. Drinking raw unpasteurized milk or consuming raw unpasteurized dairy products is certainly an unnecessary and avoidable health risk.

Introduction of raw milk contaminated with foodborne pathogens into dairy processing plants also represents an important risk of contamination of milk products. These significant exposure pathways pose a risk to the consumer from direct exposure to foodborne pathogens in unpasteurized dairy products, as well as dairy products which are re-contaminated in the post-pasteurization processing environment.

What you can do

Most fecal and foodborne pathogen contamination occurs during the harvesting of raw milk (milking, collection, and storage). However, the overall farm environment plays a major role in the presence of foodborne pathogens in bulk tank milk, too.

Reducing contamination requires excellent milking hygiene practices, proper sanitation of milking equipment, and maintaining a clean, dry environment for dairy cows. Ask the milk-quality specialist at your co-op or your veterinarian to help you evaluate your existing practices and find ways to improve them.

Foodborne pathogens, milk quality and dairy food safety are all interrelated. Producing a safe, abundant and nutritious food supply should be the goal of every dairy producer.  

Stephen Oliver is a professor in the Department of Animal Science & Co-Director of the Food Safety Center of Excellence at The University of Tennessee, Knoxville.