Foodborne Pathogens Can Lurk Around the Farm Environment

Ginger Fenton, PhD PennState Extension

The possible presence of foodborne pathogens is a concern to all dairy producers, farms that have value-added dairy businesses should be extremely vigilant.

Photo: Ginger Fenton

Foodborne pathogens can be found throughout the farm environment in manure, bedding, and animal feed including silage. The possible presence of these disease-causing microorganisms is a concern to all dairy producers, but farms that have value-added dairy businesses should be extremely vigilant. With changes in consumer purchasing habits, uncertain milk markets, and an interest in viability and sustainability, some farms have turned to value-added enterprises. These ventures include direct sales of milk in states where permitted, processing cheese on farm, and agritourism. Farm entrepreneurs can feel more confident in the safety of their products by recognizing sources of pathogens and understanding how to minimize contamination risks.

Silage can be a potential source of pathogens that are detrimental to humans and animals. However, implementing good silage management practices can minimize exposure. Examples include harvesting at the right time, properly functioning equipment, packing and covering the storage structure to exclude oxygen, possibly using inoculants and additives to aid in fermentation, and having employees follow safety protocols. Additionally, traffic control on the farm to prevent cross-contamination and restricting access to protected feed or calf areas can limit the spread of pathogens. Good hygienic practices especially when feeding and milking are encouraged.



A foodborne pathogen that is often associated with silage is Listeria monocytogenes (Driehaus et al, 2018). This persistent pathogen is a nemesis of food processors. Human and animals can experience serious health consequences including death due to this organism. L. monocytogenes has been isolated from various environmental sources including soil, water, and manure. Forage crops ensiled by wrapping, bagging, or storing in bunker silos can potentially be contaminated. When conditions are favorable for L. monocytogenes, such as when silage has fermented poorly, bacteria may multiply rapidly (Queiroze et al. 2018). Attention to the ensiling process to decrease pH and exclude oxygen will limit the resources available to bacteria for survival and growth. Anytime new material is added to a storage structure is an ideal time for the harmful bacteria to multiply due to exposure to oxygen and elevated pH before it ferments. Most pathogenic microorganisms need specific conditions to grow including a food source, the proper pH, moisture, time, and a specific temperature range. Some also need oxygen while others do not or require only a limited amount. Pathogens can be reduced or eliminated by taking away the resources they need for survival. Pasteurization or other lethality treatments of milk and dairy products such as the acidification or drying reduces or eliminates the risk due to pathogens.

Poor quality silage has been reported as a factor for contamination of raw milk related to cow cleanliness and bacteria in feces (Sanaa et al., 1993). A thorough udder preparation routine prior to milking can reduce the possibility of milk contamination as well as feeding good quality silage. Value-added processors need to be aware of the ability of L. monocytogenes to survive refrigeration temperatures and potentially cause problems should post-processing contamination occur. To prevent cross-contamination of the processing environment and food products, implement and reinforce good hygiene practices. Limit access to the processing facility to avoid carrying the pathogen into the environment on clothes or boots. Enforce a policy that restricts farm personnel from entering the processing facility when they have been around silage. Develop and implement a thorough sanitation program for the processing area and conduct routine monitoring to ensure the effectiveness of the program.

L. monocytogenes can be found throughout the farm environment. An association between poor ensiling practices and pathogenic bacteria has been demonstrated, so be prepared for harvest and implement a plan for making good quality silage. Minimizing the risk of illness from L. monocytogenes and providing a safe, high quality product should be a goal for all dairies including value-added enterprises.




Driehaus F, Wilkinson JM, Jiang Y, Ogunade I, and Adesogan, AT. 2018. Silage review: Animal and human health risks from silage. J Dairy Sci 101:4093-110.

Queiroz OCM, Ogunade IM, Weinberg Z, and Adesogan, AT. 2018. Silage review: Foodborne pathogens in silage and their mitigation by silage additives. J Dairy Sci 101:4132-42.

Sanaa M, Poutrel B, Menard JL, and Serieys, F. 1993. Risk factors associated with contamination of raw milk by Listeria monocytogenes in dairy farms. J Dairy Sci 76(10):2891-8.


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