Infectious diarrhea in foals is a significant health concern that can lead to dehydration, weight loss, and systemic illness. Without timely intervention, it can lead to severe complications and even be life-threatening.

Diarrhea in foals can be caused by a variety of pathogens including bacteria, viruses, and parasites. Signs of infectious diarrhea include watery feces, decreased appetite, lethargy and weakness.

Foals are particularly susceptible to infectious diarrhea because their immune system is not fully developed. Their gut microbiome, which plays a crucial role in fighting infections, is also not yet well-established.

Treatment must be administered promptly and may consist of fluid therapy, electrolyte supplementation and antibiotic medications. Through a combination of good management practices, vigilant observation, and prompt veterinary care, the risks associated with infectious diarrhea in foals can be significantly reduced.

Infectious Diarrhea in Foals

Diarrhea refers to an increased volume or fluidity of the feces, resulting in the passage of frequent, watery stool. Diarrhea is a common condition in foals, with one study reporting a prevalence of 48% in foals from birth up to the age of two months. [2]

Unfortunately, diarrhea frequently results in death of affected foals, particularly those under 7 days of age. [1] Early recognition of the signs of diarrhea by breeders is crucial to allow rapid medical intervention and reduce the risk of mortality. [1]

Treatment is primarily supportive in nature, and focuses on maintaining hydration, nutritional support, and protecting the gastrointestinal lining. Specific medications that target the cause of the diarrhea are added to these support measures to complete the treatment plan.

The most common causes of infectious foal diarrhea are: [1]

  • Salmonella
  • Clostridium
  • Rotavirus
  • Cryptosporidium
  • Strongyloides

For all of these infections, early identification and treatment are essential for a good prognosis for the foal.

Risk Factors

Several studies have identified common environmental and management factors that contribute to a heightened risk of diarrhea in foals. Common risk factors include: [1][2][12]

  • Mares that are not vaccinated against rotavirus prior to foaling
  • Administering antibiotics to the foal
  • Foaling in a stall
  • Not receiving adequate colostrum (failure of passive transfer)
  • Inadequate deworming of the mares prior to foaling
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Symptoms of Infectious Diarrhea

The symptoms of foal diarrhea are typically related to severe dehydration. In addition to diarrhea, foals may exhibit signs such as: [1][2]

  • Colic
  • Distention of the abdomen
  • Sunken in eyes
  • Prolonged skin tent
  • Lethargy
  • Weakness
  • Grinding teeth
  • Fever or hypothermia

Systemic Inflammatory Response Syndrome

Some foals develop systemic inflammatory response syndrome (SIRS), in which the infection triggers an inflammatory response spread widely throughout the body. Symptoms of SIRS include: [2]

  • Red gums
  • Rapid heart rate
  • Rapid breathing
  • Cool extremities, including the ears
  • Weak pulses
  • Recumbency

Without treatment, foals affected by SIRS may become comatose or die.

Treatment for Diarrhea

Treatment protocols for foals with diarrhea generally follow a standard approach, focusing primarily on maintaining hydration, protecting the integrity of the intestinal tract, and providing nutritional support.

Once these priorities are addressed, the veterinarian may introduce additional treatments tailored to the specific cause of the foal’s diarrhea for a more comprehensive treatment plan.

Maintaining Hydration

Due to the large amount of fluid excreted in diarrhea, foals with diarrhea are prone to becoming dehydrated. Dehydration directly impacts the function of internal organs, particularly the kidneys, and may lead to organ failure if not corrected. [1][3]

To address dehydration, veterinarians provide intravenous fluids. The volume of intravenous fluids provided depends on: [3][4]

  • The level of dehydration when treatment begins
  • An estimation of how much fluid the foal is losing per day in diarrhea
  • The amount of fluid required to sustain a healthy foal

Foals receiving intravenous fluids require close monitoring, as they are prone to developing overhydration from this treatment. [3] The amount of fluids requires constant recalculation by the veterinarian to prevent overhydration, particularly as the diarrhea resolves and the foal begins to feel better. [3]

Depending on the electrolyte balance of the foal, your veterinarian may also add electrolyte minerals to the intravenous fluids. Common electrolytes to add include sodium, bicarbonate, and potassium. [2][4]

Protecting the Intestinal Tract

When foals develop diarrhea, their intestinal tract becomes highly susceptible to damage. Some bacteria that cause diarrhea produce endotoxins, which can directly damage tissue if they bind to the intestinal lining. [4]

To prevent this damage, veterinarians often administer gastroprotectants, such as bismuth or kaolin/pectin, which coat the intestinal lining to reduce exposure to endotoxins. [2][4] Some products, such as activated charcoal and di-tri-octahedral smectite, can bind endotoxins directly and prevent damage. [2][4]

Many veterinarians administer antibiotics to foals with diarrhea, even in viral or parasitic infections, to target any potentially harmful bacteria in the intestinal tract and prevent them from entering the bloodstream. [2][4]

Probiotics may also be beneficial as the probiotic bacteria compete with the toxin-producing bacteria for nutrients, reducing the production of toxins. [4]

However, not all foals respond favorably to oral probiotics and some may be more prone to diarrhea. [15] Discuss this option with your veterinarian before giving your foal probiotics.

Foals with diarrhea are highly stressed, which makes them susceptible to stomach ulcers. Prolonged time between feeding, extended time laying down, and use of NSAIDs have also been identified as potential causes of gastric ulcers in young foals. It is estimated that between 25 – 57% of foals have gastric ulcers. [13]

Many veterinarians use medications such as sucralfate, ranitidine, or omeprazole to reduce the risk of ulcers. [4][13]

Nutritional Support

Foals with diarrhea are often unwilling to nurse, which makes it critical to provide nutritional support to prevent starvation. In some cases, milk from the mare can make diarrhea worse, as the large proteins it contains encourage more water to enter the intestinal tract. [4] Foals may need all of their nutrition to come from other sources.

For foals that can tolerate milk, there are three options:

  • Allowing the foal to nurse
  • Bottle feeding milk
  • Nasogastric intubation (tube feeding)

Ideally, the foal will have enough energy and strength to nurse or suckle from a bottle. [5] For weak foals that cannot nurse or suckle, a nasogastric tube allows delivery of milk directly to the stomach. [4] Regardless of the feeding method, foals require frequent feeding, typically every one to two hours. [2][4]

Foals that cannot tolerate milk have their nutrition delivered intravenously, as part of their fluids. The veterinarian will make a special fluid mixture that contains sugars, proteins, fats, vitamins, and minerals at the appropriate level for the foal’s age and weight. [4][5]

Foals should be transitioned to milk as soon as possible to prevent long-term complications. Providing only intravenous nutrition does not stimulate the cells of the intestinal lining to function properly. [4][5]


Rotavirus is the most common viral cause of diarrhea in foals, primarily affecting young foals between 5 and 35 days of age. [4][6] Foals acquire the virus when they ingest contaminated materials, including fecal matter in their environment. [6]

After infection, the virus replicates in the cells of the intestinal lining, causing destruction of the lining and preventing normal absorption of nutrients. [6]

Rotavirus can also interfere with processing of lactose, the main sugar in the mare’s milk, resulting in large amounts of the sugar remaining within the intestine. These sugars pull water out of the bloodstream into the intestinal tract, worsening the diarrhea. [6]

Rotavirus Treatment

Treatment primarily involves supportive care. Antiviral medications have not been proven effective against this pathogen in foals. [1] Most veterinarians use a combination of fluid therapy, nutritional support, gastrointestinal protectants, and antibiotics to support the foals until their bodies naturally recover.

Because this virus can interfere with lactose processing, consuming milk can be problematic for foals with rotavirus. Treatment options include restricting milk consumption and using intravenous nutrition temporarily, or administering lactase, the enzyme that breaks down lactose. [6]

Rotavirus Prevention

Like many infectious diseases, preventing rotavirus infections relies on strict biosecurity practices and minimizing exposure of foals to the virus. Any affected foals must be quarantined away from other foals to reduce spread of this disease. [6]

Any areas where affected foals have been must be disinfected thoroughly using chlorine-based or iodine-based disinfectants. [6] Regular hand-washing, the use of gloves and other personal protective equipment, and foot baths are recommended for all individuals handling the affected foal. [6]

Vaccines are available against rotavirus that are licensed for use in pregnant mares. These vaccines are given prior to birth, so that the antibodies the mare produces against rotavirus are present in her colostrum for the foal to consume. [6]

Studies on these vaccines have mixed results, with some showing no effect or only mild reduction in severity of disease. [6]


Salmonella is a particularly severe cause of diarrhea in foals, as it can often lead to septicemia (bacteria within the bloodstream). Foals that develop septicemia can develop infections in the bones, joints and other locations, as well as diarrhea. [1] As a result, the prognosis for foals with Salmonella diarrhea is guarded. [7]

Most foals acquire Salmonella through ingesting the bacteria from a contaminated environment. [2] Salmonella most commonly affects foals between 1 and 3 months of age. [8]

The prevalence of Salmonella diarrhea ranges between 1 – 17% depending on the study, geographic location, season, and population sampled. [9][10]

Salmonella Treatment

Antibiotics specifically used for Salmonella include amikacin, ceftiofur, or cefotaxime. [1]

Some veterinarians may have access to hyperimmune plasma, which is plasma taken from a horse who has developed an immune response to Salmonella endotoxins. Administering hyperimmune plasma can improve survival rates by stimulating the foal’s immune system. [1]

Salmonella Prevention

Foals acquire Salmonella from their environment, so strict biosecurity protocols are the best method of prevention.

Any affected foals should be quarantined away from other horses until they have had at least 5 negative tests for Salmonella. [1] Any areas contacted by the affected foal should be cleaned thoroughly before other horses are introduced. [1]

Salmonella is endemic on some farms, meaning that it is not easily removed from the environment even with rigorous cleaning practices. Vaccination against the specific strain of Salmonella present on their farm can reduce the number of foals developing diarrhea. [1]

The veterinarian administers these vaccines to pregnant mares prior to foaling so that the antibodies produced by the mare are transferred to the foal in their colostrum. [1]


Clostridium difficile and Clostridium perfringens are some of the most common causes of foal diarrhea, particularly in newborn foals under 5 days of age. [1][10] In severe cases, foals may be found dead before they show any symptoms of diarrhea. [1][2]

These bacteria are commonly associated with use of antibiotics or with stress in adult horses. However, young foals can be affected even without any antibiotic use or stressful events. [4][9]

Clostridium Treatment

Clostridiosis is the scientific name for the bacterial infection caused by Clostridium species. Specific treatment for clostridiosis involves the use of metronidazole, an antibiotic that also has anti-inflammatory properties in the intestinal tract. [4]

Some strains of Clostridium are resistant to metronidazole, so your veterinarian will likely perform a culture and sensitivity test on the foal’s feces to select the most effective antibiotic. [11]

Clostridiosis can also affect the intestine’s ability to process lactose. For this reason, some veterinarians may administer the enzyme lactase to help reduce diarrhea. [4]

Clostridium Prevention

Clostridium bacteria produce spores, which are hardy forms of the bacteria that are virtually impossible to eliminate from an environment. [4] Prevention of clostridiosis primarily relies on rigorous biosecurity and thorough cleaning of foaling areas to reduce risks as much as possible.

In particular, keeping the foaling environment free of manure is crucial. The bacteria are primarily spread through fecal contamination. [4]


Cryptosporidium parvum is a protozoan parasite that commonly affects foals between 4 – 21 days of age. [1][4] Typically, diarrhea from Cryptosporidium resolves on its own within 1 – 8 days. [7][9]

Cryptosporidium Treatment

Treatment is primarily supportive, involving fluids and nutritional support. Some studies suggest that antiparasitic medications such as paromomycin may be beneficial; however the evidence is lacking in foals. [4]

Cryptosporidium Prevention

Due to the highly infectious nature of the parasite, any affected animals must be isolated from all other animals to prevent the spread of infection. [1] These environments must be thoroughly disinfected before introducing other animals into the area, using agents such as bleach or hydrogen peroxide. [1]

The most significant concern with Cryptosporidium is that the parasite is highly infectious to humans, requiring careful handling of any affected animals. [1] Personal protective equipment (PPE) such as gloves and single-use coveralls are recommended for anyone handling an affected foal.


Strongyloides westeri is a nematode (roundworm) parasite that primarily affects foals. Foals acquire the nematode by consuming larvae in the dam’s milk, which allows the larvae to proliferate in the foal’s intestine. [1][4]

When present in large numbers, Strongyloides can cause diarrhea in foals.

Treatment and Prevention

Ivermectin or oxibendazole are the main medications for treating Strongyloides in foals.[1]

Administering ivermectin to the broodmare immediately after birth has been shown to be effective in preventing the transmission of larvae through the mare’s milk. This is the primary preventive measure currently employed against this internal parasite.

However, using ivermectin in lactating mares may result in the foals have less than optimal exposure to ivermectin, allowing worms to develop drug resistance. [14]

Your veterinarian can advise you on a specific deworming protocol for your broodmares, including the timing and dosage of medications.


  • Diarrhea is common in young foals and can cause serious consequences, including death, if left untreated
  • The most common causes of infectious diarrhea in foals are rotavirus, Salmonella, Clostridium, Cryptosporidium and Strongyloides
  • Treatment of diarrhea in foals focuses on maintaining hydration, providing nutritional support, and protecting the gastrointestinal lining
  • Strict biosecurity practices are crucial for prevention of all types of infectious diarrhea in foals

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