• Posted by Dr. Charles Hofacre

Improving Salmonella Controls to Maintain Consumer Trust

As we have known for a long time, Salmonella organisms follow a simple process over the course of their life:

  1. Get into the intestinal tract of a host animal;
  2. Multiply;
  3. Get out of the host animal alive; and
  4. Find another intestinal tract as soon as possible.

Controlling Salmonella is simply a matter of disrupting this process. In 1984, the American Association of Avian Pathologists came up with a list of seven interventions for reducing the overall incidence of Salmonella throughout the poultry industry. These recommendations have remained the same ever since.

  1. Reduce Salmonella from breeders
  2. Reduce Salmonella in feed
  3. Drinking water sanitation
  4. Competitive exclusion
  5. Antibiotic treatment
  6. Vaccination
  7. Farm cleaning and disinfection

In this post, we’ll focus on the second intervention listed above: reducing Salmonella in feed. In a typical live production biomap, there are four locations where feed-based interventions can have an effect on Salmonella: at the primary breeder, at the placing of pullets, as pullets are moved to the layer, and at the broiler farm.

At each of these four points we can reduce the prevalence of Salmonella through biosecurity, reduction from inputs, and proactive interventions. Keep in mind, however, that we may not be able to completely eliminate Salmonella through any one intervention. This is why it is important to treat Salmonella control as a numbers game and enact multiple interventions.

Even in feed, we should control for Salmonella at multiple points, not just one. In fact, there are four actions we should take to ensure that our feed has the lowest risk possible for Salmonella:

  1. Obtain raw ingredients with minimum risk of Salmonella
  2. Decontaminate finished feed
  3. Prevent recontamination of feed as it is stored and transported
  4. Monitor the process

The first potential source of Salmonella in feed is raw ingredients. We know that animal byproducts are the highest risk ingredients for Salmonella contamination — some studies have shown contamination rates of up to 74 percent. Poultry meal is an ingredient of particular concern, due to the fact that Salmonella serovars that are present in poultry meal are more likely to successfully colonize a chicken than serovars present in swine or cattle byproducts. Cereals and vegetable oils also tend to be lower risk.

For breeders, it is especially important to avoid high-risk feed ingredients, as a breeder flock that becomes infected with Salmonella could result in hundreds of thousands or millions of broilers being infected further down the biomap.

Ingredient purchasing and feed monitoring is especially important for breeders, given the risks that can occur in breeder flocks and further downstream. If you are considering applying extra salmonella controls at any point in the biomap, I would recommend taking special precautions with your breeder feed.

The primary tool for feed decontamination is heat treatment, which occurs in the conditioner and pellet mill. The effectiveness of heat treatment in reducing Salmonella is dependent on time, temperature, moisture, numbers and thermal resistance of contaminants. It is important to note that certain serovars are more resistant to heat treatment than others. Salmonella senftenberg, for example, can tolerate higher levels of heat than many other serovars.

We know that moisture levels play a role in the effectiveness of heat treatment — it is easier to kill Salmonella with heat treatment when there are higher levels of moisture (over 18 percent).

While heat treatment in the pelleting process reduces Salmonella by 90 percent, recontamination leads to a final reduction of only 81 percent.

One of the primary locations where recontamination can take place is the pellet cooler, where dust pulled in by the air to cool the pellets and this dust can have Salmonella on it. The warm, moist environment of the cooler is ideal for Salmonella to live and grow and recontaminate the already decontaminated pellets.

Roof rats, Norway rats, and house mice can all affect feed mills and serve as a major source of recontamination for heat-treated feed. While rodents are a year-round threat, evidence shows that they are more likely to enter feed mills during the fall months, so it is most important to protect against rodents between September and December.

Depending on local regulations, we can decontaminate feed beyond heat treatment in several ways: with organic acids, with combinations of different organic acids, or with combinations of organic acids and formaldehyde. We can apply these products to raw ingredients, in the mixer, or spray them onto finished pellets. These organic acid and formaldehyde formulations serve both to reduce Salmonella contamination in the mill and to reduce Salmonella survival upon recontamination.

Evidence shows that the use of organic acids with formaldehyde alongside heat treatment can result in a significant reduction in the presence of Salmonella, as well as a significant reduction in recontamination.

The necessary complement to all Salmonella controls is monitoring — this is the only you can ensure your controls are working. I recommend taking samples from feed mill dust, high-risk ingredients (animal byproducts and protein sources, in particular), and feed trucks on a regular basis. Spot checks of other inputs (like grains) can round out your monitoring strategy.

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