Pathogens are microorganisms that cause illness. They include bacteria (salmonella and campylobacter, for example) and viruses (such as avian influenza, ASF and PEDv).
Pathogens can thrive in both feed and raw ingredients. By providing all the essential components pathogens need to live, and in the case of bacteria reproduce, feed is a near-perfect environment for these microorganisms.
From feed, pathogens can infect livestock and enter to the food chain where their impacts can be devastating. Millions of human lives are lost each year due to the illnesses pathogens cause. These disease outbreaks also cost the food and farming industries billions each year through poor livestock performance and damaged business reputations.
What makes feed an ideal environment for pathogens?
Feed and its raw ingredients are generally kept at temperatures well within the that virions survive and bacteria reproduce. The moisture content, even post heat treatments or pelleting, is also sufficient for bacteria and viruses to thrive.
Many of the nutrients that livestock demand - and are therefore abundant in feed - are also needed by bacteria. Carbon, nitrogen, salts, vitamins and minerals are good examples.
While some bacteria and viruses can survive in very alkaline and very acidic conditions, most thrive in neutral environments. Research by the USDA demonstrated that most feed ingredients and feed pre-enrichment offers bacteria and viruses a close to neutral environment. The pH of broiler and layer feed, for example, ranged from 6.2 to 7.0.
With ideal temperatures and pH, together with the availability of oxygen, moisture and nutrients, feed can be a breeding ground for bacteria and a home for viruses.
How do pathogens contaminate feed?
Raw ingredients can be contaminated by pathogens such as salmonella, campylobacter and avian influenza, in the field. Wild animals such as birds, rodents and wild boar can spread bacteria and viruses through their feces but also on their fur and feet as they feed on, or travel across crops.
Feed ingredients can also be contaminated if they come into contact with the residues of contaminated feed ingredients during harvesting, storage and transportation.
When these ingredients reach the feed mill, further contamination is likely. Many pathogens and even some viruses are susceptible to heat. But heat treating or using acids to control them on arrival at the mill, or when they are processed into compound feeds, doesn’t solve the problem. Salmonella, for example, is widely known to live in the cooler. Air used to reduce feed temperature often contains contaminated dust and spreads bacteria.
Once feed is contaminated, viruses are highly likely to survive and bacteria will multiply. This is particularly important where feed is stored.
Our understanding of how pathogens contaminate feed is deepening. The technology and tools we use are becoming more sensitive, enabling us to identify not only the presence of bacteria, but the type and its origin too. In 2020, for example, Shariat et al (2020) used CRISPR-SeroSeq as a tool to reveal to specific Salmonella serotypes and their frequency in feed. Through this, and other on-going research, we’re better able to track pathogens, develop mitigation strategies and improve feed safety.
What are the consequences of pathogens in feed?
Even pathogens that don’t infect humans will impact livestock performance, meaning higher costs and reduced outputs. Some pathogens, like Clostridia and E. coli, damage the immature guts of young birds, reducing the uptake of nutrients, limiting performance for their entire productive life. Pathogens in feed can also increase veterinary costs, make livestock more susceptible to other illnesses, increase mortality and reduce uniformity.
Where pathogens in feed subsequently infect humans, the impacts can be devastating – not only for the manufacturer, but for the livestock producer, the food processor, the retailer and consumers.
Throughout the supply chain, business reputations can be severely damaged. Farmers can lose whole flocks, herds or droves and with them, valuable genetics which have often taken generations to develop. At the end of the food chain, consumers can lose their lives.
Salmonella, for example, causes 1.35 million illness, 26,500 hospitalizations and 420 deaths each year in the United States. It’s estimated to cost the American economy $3.7billion.
What can be done to control pathogens in feed?
Controlling pathogens in feed requires action throughout the production process. Strict hygiene and biosecurity practices on farm and in the mill will help prevent further contamination.
Cleaning machinery and equipment used in the production process, preventing rodents’ access, together with ensuring employees don’t introduce pathogens to the mill, are all essential elements of good hygiene procedures.
In addition, feed manufacturers can heat treat feed and apply products known to by highly effective in killing pathogens. Products that offer residual control offer protection against re-contamination during packaging, transport and storage.