Scours: How do we know what we are looking at?

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Having cases of diarrhea occur in baby calves presents the cow-calf producer with many questions—the first of which may be, “What germ is causing this problem?”

There are some good reasons to know the answer to that question.  Knowing the pathogens present in a calf scours outbreak can help guide decisions about treatments if they are specific for one germ or another (e.g., coccidiosis).  On a prevention basis, future pre-calving vaccination programs can be more effectively tailored to a herd when specific pathogens are identified. 

On the other hand, many interventions during a scours outbreak are the same regardless of the germs identified.  For example, providing sick calves with fluids and electrolytes are an important part of treating all cases of calf diarrhea.  Many scours outbreaks are the result of overwhelming exposure to contaminated calving lots or barns; methods of reducing that exposure are the same regardless of the specific germ(s) present.  Finally, many scours outbreaks are the result of more than one type of germ, which makes sorting out these cases more difficult. 

The only definitive way to identify the germs present in scours outbreaks is an analysis by a veterinary diagnostic lab.  Short of that, however, there are some factors that producers can keep in mind:

  • Age of onset.  Considering that exposure to scours germs for most calves occurs in the first hours of life, and that these organisms all have their own incubation period, calf age at the onset of diarrhea may provide some important clues.  Pathogenic E. coli strains and Type C Clostridium perfringens infections affect calves very early in life: 0-5 days of age.  Viruses such as rotavirus and coronavirus typically affect calves from 4 to 21 days of age.  Cryptosporidium generally affects calves from 7 to 28 days, and coccidiosis usually no earlier than 28 days of age.  Keep in mind that these times can all vary depending on exposure and immunity levels. 
  • Color of the scours.  Relying on color of the calf’s diarrhea to identify specific pathogens is generally not useful.  This color is very dependent on what else the calf has been ingesting (milk, mud, grass, medicine?) and can vary widely from calf to calf and farm to farm.  One exception does seem to exist, in that calves with acidosis due to dehydration and electrolyte imbalances often exhibit a greyish tint to their feces—but this is not specific for an organism. 
  • Blood, mucus, and other substances.  Clots of red blood indicate some fairly severe damage to the intestine.  Bloody stools usually point towards coccidiosis in older (> 4 weeks) calves and can occur more rarely in cases of Clostridium perfringens Type C infections in calves less than a few days old.  Excessive mucus sometimes is an indicator of irritation in the lower digestive tract. 

Sorting out the possible causes of calf scours is always something producers should approach with help from their local veterinarian.  With a general sense of the causes of scours in cattle, aspects of the disease such as treatment, prevention and control can be addressed.  We’ll discuss these aspects in subsequent iGrow articles.

Source: Dr. Russ Daly


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