Section 2 | Tackling Diarrhea in Young Calves

Ontario Beef Industry
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What is Causing Diarrhea?

We call the infectious bugs (bacteria, viruses, and parasites) that cause disease “pathogens”.


Many pathogens are responsible for causing diarrhea in beef calves. Some of the major infectious causes include:


  1. Bacteria

    • E. coli
      • There are many strains of coliform bacteria that can infect calves, but of most importance is K-99 E. coli. This strain of E.coli is able to attach to the intestinal cells and release a toxin that causes the secretion of water and electrolytes from the cells. The loss of fluid can be very rapid


    • Salmonella
      • Salmonella destroys intestinal cells. This makes the cells of the gut very leaky, and prevents the absorption of fluid, and digestion of milk
      • Salmonella can also invade the blood and cause severe illness in calves


  1. Viruses: Rotavirus, coronavirus

    • These viruses infect intestinal lining cells and destroy them. This makes the gut cells very leaky and prevents the absorption of fluid and digestion of milk


  1. Parasites: Cryptosporidium

    • Cryptosporidium causes a similar effect to rota- and coronavirus


Regardless of how these pathogens work, the outcomes are similar – there is significant fluid and electrolyte loss in these calves.

It is important to note that in many cases of diarrhea, a bacterial pathogen is not involved. Thus, not every calf with diarrhea needs to be treated with antimicrobial medications. Antimicrobials should only be prescribed for calves with systemic signs of illness (e.g. calves that are dull or depressed, have decreased appetite or activity, or the presence of an elevated rectal temperature) or if blood is found in the manure.

When testing for the cause of diarrhea, it often takes several days to get results from a laboratory. For this reason, it is not practical to base immediate treatment decisions only on laboratory results. That’s why it is important to evaluate the clinical situation of the calf. Beyond initial treatment, it is still important to diagnose the pathogen responsible for causing diarrhea. It enables you and your veterinarian to develop and implement specific strategies to prevent diarrhea from occurring or recurring.

When animals become ill, it can also be helpful to evaluate some key aspects of animal husbandry to evaluate if management changes may be necessary to reduce the incidence of disease. Monitoring and recording is also important to monitor morbidity levels and assess trends and progress over time.