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Assess your risk to solve the clostridial puzzle

Tom Rehberger for Progressive Dairy Published on 30 September 2019

Clostridial diseases can be among the most puzzling problems on a dairy. That’s because C. perfringens and other clostridia species occur naturally in soils, water and throughout the dairy environment.

These bacteria usually are not a problem until stressors cause them to flare up and produce potent toxins that lead to severe illness or even cow death.



It’s hard to predict clostridial disease risk because problems may be sporadic and infrequent – yet devastating when they occur. Dairies across North America experience a huge variation in clostridial risk – not only from region to region and farm to farm but also from cow to cow within an individual herd.

Even on well-managed dairies, a certain percentage of cows without outward symptoms likely have ongoing subclinical clostridial infections that could reduce their performance. Managing clostridial risk in your herd can help you maintain your margins by preventing costly losses due to these invisible, yet highly damaging, pathogens.

Our researchers have analyzed clostridial risk on dairies since 2015. Tests of 14,553 fecal samples from 369 farms in 27 states – representing more than 11 percent of the U.S. dairy herd – show that more than half of samples fall in a “high-risk” category based on the levels of clostridia bacteria found in the samples.

Risk factors

To understand clostridial disease risk, it’s important to realize clostridia live naturally in the cow’s lower gastrointestinal (GI) tract without causing problems until certain factors trigger the outgrowth of these bacteria. The resulting higher populations produce toxins and metabolites that lead to clinical disease and metabolic problems.

Several predisposing factors favour clostridial outgrowth in the GI tract:


  • Off-feed events. After cows go off-feed due to weather, crowding or other issues, they typically then go into “slug feeding” mode. The resulting heavy influx of energy into the GI tract can stimulate clostridial growth.

  • Feed contamination. Soil-borne contamination is one of the biggest contributors to clostridial content in feed. For example, if alfalfa or grass is cut close to the ground, soil can be pulled into the harvested forage, bringing clostridia with it. Heavy rains can contaminate feed by splashing mud onto plants prior to harvest. In ensiled forages, excess moisture or poor silage-making practices can create aerobic conditions that lead to greater clostridial growth.

  • Clostridial growth after mixing. Clostridia can grow in the TMR if silage bunk faces are not managed properly. Exposure to oxygen creates the opportunity for feed spoilage and higher clostridial bacteria populations.

  • Bypass starch to the lower GI tract. Starch not utilized in the rumen moves to the lower GI tract, where it releases energy that feeds clostridial bacteria.

  • Excess bypass protein. While it’s beneficial for protein to bypass the rumen, excess amino acids in the intestines also feed clostridial populations, leading to outgrowth issues.

  • Other stresses. Dirty, crowded pens can cause cows to consume clostridial bacteria from the environment. Even stray voltage creates animal stress that can cause clostridial populations to flare.

Mitigating risk

Managing these external factors can help mitigate clostridial risk on the dairy by reducing the opportunity for bacteria to enter the cow and grow to harmful levels.

Considering the widespread incidence of clostridia, it’s also important to work within cows’ digestive systems to reduce clostridial populations and make animals more resilient against these dangerous bacteria.

One strategy is feeding microbial additives containing Bacillus strains that combat clostridia by inhibiting their growth. Bacillus work to modulate the microbial communities in the rumen and GI tract, reducing harmful clostridia and increasing beneficial bacteria populations. Long-term Bacillus feeding ultimately changes clostridial population levels and species diversity. In addition, these beneficial bacteria control inflammation in the animal and serve as a barrier to protect the GI tract.

On-farm data shows targeted microbial solutions containing Bacillus can reduce risk from clostridia at both the individual cow and herd level. Our researchers compared risk levels on the 32 sampled dairies both pre- and post-feeding. After feeding the additive, the percentage of samples in the “high-risk” category for total clostridia fell from 52% to 34%. When looking at C. perfringens only, the percentage of samples considered high-risk fell from 27.9% to 17.4% after feeding the additive.

Herd-specific solutions

Since clostridial strains differ from region to region and farm to farm, it is important to develop feed additive solutions specific to each situation. The process starts by gathering and analyzing manure samples to assess bacterial challenges throughout the farm. That provides information to determine which strain or strains of beneficial Bacillus will best address the harmful organisms found on the dairy. Individualized feed additives are then formulated to address those specific challenges.

Dairies implementing these feed solutions have not only seen clostridial populations drop, they have also observed more consistent manure and feed intakes, fewer off-feed events, fewer cows in the sick pen and fewer GI-related deaths – all leading to a positive response in energy-corrected milk.


Clearly, even subclinical clostridial infections can be a drag on cow health and productivity, making it worthwhile to take clostridia risk seriously and solve this puzzle in your herd. end mark

Tom Rehberger
  • Tom Rehberger

  • Director of Innovation and Product Development
  • Arm & Hammer Animal and Food Production
  • Email Tom Rehberger