Foal Diarrhea: A Smelly Situation

By Garrett Metcalf, DVM

This time of year is a wonderful period when new life is brought into the world for many farmers and ranchers, especially those foaling horses. After counting the days, preparing the barn and many sleepless nights, for some the hard work has paid off and a new foal is in the stall waiting. You have done your homework on all the milestones that a foal needs to meet to have the best start to life, and the foal meets them all with no problems. The following day or two you notice the foal has loose stool on its tail and is not as active as it should be. The questions start flowing, and the biggest one is what do we do now?

First thing to know is that not every diarrhea or its cause is the same. There are many causes of diarrhea in newborns. They can be separated in categories of infectious and non-infectious diarrhea. Infectious causes are obviously the most serious and concerning causes. Infectious diarrhea can be caused by bacteria, viruses and parasites.

Viral causes of diarrhea are rather common among foals especially in larger herd operations. Rota and Corona viruses are the leading causes of viral diarrhea in young foals and can lead to outbreaks in a breeding farm quite readily. Rotavirus has an incubation period of about three-10 days, meaning that the time the foal is exposed to the time it starts showing clinical signs of diarrhea or illness

Bacterial causes of diarrhea commonly seen are Clostridia, Salmonella, E. coli species and even Rhodococcus.

Non-infectious is usually associated with establishment of normal bacterial flora in a foal’s gut when it begins to ingest manure from the mare and eating hay. This time period is commonly referred to as foal heat diarrhea, but does not have anything to do with the hormone cycle that the mare is experiencing or changes in the content of the mare’s milk. Non-infectious diarrhea usually is self-resolving and does not require anything other than monitoring.

To help put the mind at ease in cases that develop foal heat diarrhea, blood work can be checked to make sure all is well, and sometimes administering probiotics can help resolve the diarrhea sooner.

Infectious causes of diarrhea need to be taken seriously because of the deleterious effects they have on the foal. Foals that become ill with one of these infectious causes of diarrhea get dehydrated rather quickly and stop nursing, further compounding the problem. Often foals will need to be hospitalized, placed on IV fluids and a feed tube placed to ensure they are getting enough nutrition. Antibiotics, probiotics, gastroprotectants and absorptive medications to help prevent absorption of endotoxins from the gastrointestinal tract are also key features of treatment of diarrhea in foals.

Pathogens can be isolated from their feces and are submitted for virus isolation and culture to determine the pathogens that are making the foal sick. This is also important information to further protect the rest of the population of horses.  Depending on the age of the foal, IgG antibody levels need to be assessed to determine if enough colostrum was consumed to provide protection for the foal. Failure of passive transfer of antibodies from the mare through colostrum to the foal puts the foal at high risk of systemic illnesses and sepsis.

Other complications from failure of passive transfer, especially in an already sick foal, are joint infections, growth plate infections and umbilical remnant infections. If failure of passive transfer is diagnosed, antibodies are replaced with plasma transfusions from donors that are kept banked and frozen until needed. The donors are often hyperimmunized for certain pathogens, and it is common in diarrhea cases to use these types of plasma products to treat foals with diarrhea against the common pathogens like Clostridia species.

Learn more about treatment and prevention in the April issue of Oklahoma Farm & Ranch.