Diarrhea in foals is common, but unlike with older horses, the condition can be much more dangerous. Foals can experience diarrhea due to a variety of factors including viruses, bacteria, parasites, or even something such as lactose intolerance. 

Foal heat diarrhea, which occurs due to normal physiological changes in the gut, is another common cause, but for the purposes of this article, we’ll focus on other, more concerning causes of foal diarrhea. 

Because foals haven’t yet established a robust immune system, they are more susceptible to infectious agents that can cause severe diarrhea. Without intervention, some causes of foal diarrhea can even be fatal.

The following are common causes of moderate to severe foal diarrhea and, if suspected, should be cause for immediate concern. 


Rotavirus, usually contracted from the environment, is a common cause of diarrhea in foals aged two days to two months. Younger foals are most susceptible to rotavirus, and on large farms, multiple foals often contract the virus at the same time. 

Rotavirus causes dehydration and electrolyte abnormalities, necessitating fluid replacement and supportive care. Foals with rotavirus should be isolated so they are less likely to spread it to other foals. The virus may be prevented by a vaccine given to the pregnant mare. 


Foals are also highly susceptible to salmonellosis, caused by bacteria that can be shed in feces and then ingested through contaminated materials. Salmonellosis is usually seen sporadically, but it can become widespread on farms under some circumstances. With this bacterial infection, stress appears to play an important role. Surgery, transport, changes in management, concurrent disease, or treatment with broad-spectrum antimicrobials often occur before the onset of diarrhea. 

Salmonella-related diarrhea is often severe in foals. Other signs in foals include pneumonia, meningitis, physitis, and septic arthritis. Severe cases of salmonellosis can be fatal if not treated. 


This is another bacterial cause of diarrhea in foals with two types: Clostridium perfringens and Clostridium difficile. The first form affects foals less than seven days old, while the second can affect foals of any age. 

Gut damage caused by clostridia bacteria causes toxins to enter the bloodstream, leading to sepsis. Diarrhea is usually bloody and the foal is critically ill, needing immediate veterinary care. 

Foals with Clostridia infection are treated with IV fluids, electrolytes, antibiotics, as well as other forms of supportive care. Vaccination is available for pregnant mares in areas where Clostridial diarrhea is prevalent. 


Parasites are yet another cause of diarrhea in foals. Strongyle worms can be transferred to foals through the mare’s milk during the first 2-4 weeks. Signs of parasites in foals include diarrhea, colic, and fever. Standard treatment is deworming with Ivermectin. Deworming the mare on the day of foaling can also help to decrease transmission of strongyle worms to the foal. 

Determining the exact cause of your foal’s diarrhea may not always be easy, but isolating them from other foals to prevent possible transmission and seeking immediate veterinary care are both important. 

The Importance of Colostrum in Preventing Foal Diarrhea

Colostrum is critical for foal health. This is the mare’s first milk which contains antibodies that will help the foal fight off viruses and bacteria during their first few months of life. However, not all colostrum is created equal, nor do all foals get enough colostrum due to a variety of reasons. 

Your veterinarian can perform a blood test at 12-18 hours of age to determine whether the foal has consumed enough quality colostrum. It’s also important to note that foals can only absorb the antibodies from colostrum during the first 18 hours of life. After that, changes in their digestive system make this impossible. 

High-quality colostrum can help prevent your foal from contracting infectious forms of diarrhea. If the foal has not gotten adequate colostrum, the best substitute is equine plasma, which can transfer needed antibodies. Your veterinarian can do this intravenously. 

Treating Foals With Diarrhea

Aside from foal heat diarrhea, all other forms of diarrhea or signs of illness in foals should warrant immediate veterinary intervention. Due to their small size and immature digestive systems, life-threatening dehydration can occur in as few as 6-8 hours. The younger the foal, the more critical the problem may be. 

Treatment for severe foal diarrhea includes IV fluids to replace electrolytes, intestinal protectants, and medications for gastric ulcers. Antibiotics are reserved for serious bacterial infections and should never be given unless prescribed by your veterinarian, as they may only complicate matters by killing off the “good” bacteria in the foal’s gut. 

Applying a protectant such as petroleum jelly around the perineum can help to prevent scalding of the skin.  

Preventing Diarrhea in Newborn Foals

Prevention of diarrhea in foals is best. To this end, good management practices can go a long way in helping. Before foaling, the mare should be properly vaccinated. The foaling environment should be kept clean and dry. 

After birth, ensuring that your foal receives adequate colostrum (or blood plasma) is of utmost importance. If your foal stops nursing or shows any signs of illness, immediate veterinary care should be sought. 

FullBucket has two specific products to aid in the prevention of foal diarrhea. We recommend these natural solutions for EVERY foal: 

  • Foal Kickstart Paste offers gut and immune support to neonatal foals. This product is designed to be used during the first 24 hours of life to get the foal off to a healthy start, as well as reduce the risk of diarrhea caused by bacteria, viruses, and/or parasites. 
  • Foal Probiotic Paste assists in the digestion and absorption of essential nutrients and supports the foal’s immune system and gastrointestinal mucosa. Suggested use is form days 2 to 7 of life. 

Using these two products together, in the foal’s first week of life, can help get them off to the healthiest start.  

Remember, foal diarrhea is a problem that can often be avoided with good management practices and preventative measures, such as FullBucket foal products. 

Photo by George Tsivras on Unsplash

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