Diarrhea in Foals

Diarrhea is extremely common in foals, but the con­dition is often self-limited. However, a few of the potential causes of diarrhea are highly contagious, and this leads to anxiety in horse owners and veterinarians when diarrhea is identified. A practical approach to diagnosis and treatment in foals with diarrhea should be a standard part of practice for the equine practitioner.

Recognition of Diarrhea

Recognition of diarrhea should be straightforward, although many diseases that lead to diarrhea begin with nonspecific signs. Foals with colic, fevers, lethargy, anorexia, or gas distension of the abdomen should be considered at risk for developing diarrhea. Recognizing early clinical signs is important not only from a therapeutic standpoint but also for infectious disease control.

Veterinarians should verify the consistency of the feces before proceeding with diagnosis and treatment in a foal in which diarrhea has been observed or described by the owners. Inexperienced horse owners often mistake the consistency of normal newborn foal feces for diarrhea, and this can lead to unnecessary veterinary testing and treatment.

Diagnostic Approach to the Foal With Diarrhea

A series of diagnostic tests is available for evaluating a foal with diarrhea, and these tests can be performed in either a field or hospital setting (Box 173-1 ). Initial testing is inexpensive and simple and is often appropriate for an otherwise healthy foal. A more comprehensive approach to testing is needed in sick animals or in herd outbreaks.

Box 173-1. Summary of a Diagnostic Approach for Foals With Diarrhea.

• 1.Physical examination*
• 2.Venous blood sample (complete blood count, chemistry panel)*
• 3.Fecal sample collection (flotation and infectious disease testing)*
• 4.Urine collection
• 5.Abdominal ultrasound
• 6.Abdominal radiographs

Physical Examination

As mentioned, the clinical examination is especially useful for confirming fever, gas distension of the abdomen, and fecal consistency. Evaluation of perfusion and hydration also deserves special attention because they can be indicators of intravascular volume status. This information can be used to gauge the need for immediate treatment and also help prioritize testing.

The veterinarian should attempt to categorize the foal into one of the following groups:

• 1.Healthy foal (no other clinical abnormalities other than diarrhea)
• 2.Stable foal with clinical abnormalities, including fever, lethargy, and decreased appetite
• 3.Compromised foal with evidence of hypovolemia or dehydration and more severe clinical signs, including colic and abdominal gas distension

Complete Blood Count

Next to the physical examination, this is probably the most useful test in helping categorize likely causes for diarrhea and the potential need for treatment. Identification of neutropenia, immature neutrophils, and toxic neutrophil changes may suggest a more severe (and potentially contagious) cause of diarrhea. Additionally, increases in PCV may be associated with dehydration and the need for more immediate treatment.

Chemistry Panel

Although the chemistry panel may be less helpful in categorizing the cause of the diarrhea, it provides important information about other potential organ injury. Specifically, azotemia is common with severe diarrhea and could potentially alter the treatment strategy. The protein concentration (both total protein and albumin) should be carefully scru­tinized. Protein-losing enteropathy is common in many conditions that cause diarrhea in foals and can result in low protein concentrations. However, dehydration is also common in these foals, which can result in increased protein concentration. A normal protein concentration may be found with mild disease, or it can also be found when protein loss is combined with severe dehydration (making interpretation particularly complex).

Fecal Sample Analysis

Obtaining a fecal sample for testing is an important part of a practical diagnostic approach. A number of simple tests can be performed, including fecal flotation for sand, fecal analysis for parasites, and infectious disease testing (Table 173-1 ). Fecal testing is such an important part of diagnosis that practitioners should make every attempt to obtain a sample. In some cases, even obtaining a fecal swab from the rectum may be adequate for certain tests. Samples can be transported in a sterile urine or fecal cup and submitted to the laboratory for testing. A fecal float for sand can be completed at the farm with a manure sample added to a small volume of water in a plastic bag; the sample is evaluated by manually palpating the consistency of the particulates that settle to the bottom.

TABLE 173-1.

Fecal Testing for Specific Infectious Diseases Associated With Diarrhea in Foals

Suspected Pathogen	Testing Available
Salmonella spp	Incubation in enrichment broth followed by fecal culture PCR testing
Clostridium difficile	ELISA test kit (easily performed on site)
Clostridium perfringens	ELISA testing at commercial laboratories
Rotavirus	ELISA testing at commercial laboratories PCR testing
Coronavirus	PCR testing
Cryptosporidium spp	Immunofluorescence assay PCR testing
Strongyloides westeri	Fecal flotation

ELISA, Enzyme-linked immunosorbent assay; PCR, polymerase chain reaction.

Urinalysis

A urine sample can be used to further evaluate kidney function, which can be important if azotemia is revealed in the foal's blood work. Some toxins (e.g., oleandrin, cantharidin) cause diarrhea, and a urine sample can be used for testing. However, obtaining a urine sample is likely to be a lower priority than obtaining a fecal sample in foals with diarrhea.

Abdominal Ultrasound

Imaging of the abdomen with ultrasound is practical and useful and can easily be performed in the field. Identification of fluid-filled large or small intestine segments may raise suspicion that diarrhea is imminent in foals with suspicious clinical signs. Additionally, inflammation or thickening of the intestinal walls can indicate disease severity and raise the index of suspicion for certain conditions. Identification of the segment of intestine affected (small vs. large) may also help the examiner prioritize the possible causes of diarrhea. Given the relatively small size of foals, a reproductive linear probe on a basic ultrasound machine can be used effectively to evaluate the intestines.

Abdominal Radiography

Evaluation for foreign material (e.g., sand, gravel, and wire) may be one of the main reasons to radiograph foals with diarrhea. The degree of gas distension can be appreciated, but this can typically also be evaluated during physical examination. Small portable x-ray units can effectively radiograph the abdomen of a foal and can help to exclude foreign material (sand) as a cause for the diarrhea.

Common Causes of Diarrhea in Foals

Foal Heat Diarrhea

Otherwise healthy foals that develop diarrhea between 5 and 15 days of age are likely to have so-called foal heat diarrhea if other causes are excluded. Although the name implies an association with the mare's heat cycle, research suggests that there is no direct relationship (except temporally). The diarrhea may be a result of changes in gastrointestinal physiology and in microflora populations that are typical at this age because of the consumption of feed and other materials in the environment. This type of diarrhea is usually self-limited, and foals typically only require close observation. Antidiarrheal products can be administered if owners are concerned about the volume of diarrhea, but these products are often unnecessary.

Pica

Depending on the environment, foals are prone to eating soil, sand, and other foreign material such as hair. Sand is abrasive and when accumulated in the bowel can cause diarrhea and colic. Diagnosis can be made by fecal flotation of manure and confirmation of soil or sand in the sample. Abdominal radiography is the most definitive means for identifying and quantifying sand (Figure 173-1 ). However, apparently healthy foals may have small quantities of sand and have no obvious clinical signs. If the owners have observed the foal consuming soil or sand, the index of suspicion for this diagnosis should be increased. In addition to the treatments outlined in the next section, foals with a substantial quantity of colonic sand may initially need treatment with mineral oil (2 to 4 mL/kg). After the sand or soil is being passed regularly, treatment with psyllium may also be administered daily, at label doses.

Figure 173-1.

Radiograph of a foal with diarrhea secondary to accumulation of a modest quantity of sand in the gastrointestinal tract.

Rotavirus

Rotavirus is considered the most common infectious cause of foal diarrhea in some regions and can be identified in foals as early as a few days of age up to several months of age. The survival rate is typically very high, with clinical signs ranging from mild to severe. Foals with rotavirus infection often have abdominal gas distension (which can be marked) and colic, in addition to diarrhea. Treatment is supportive and usually very effective. Rotaviral enteritis is highly contagious and is an important consideration for breeding farms and veterinary practices. Accelerated hydrogen peroxide compounds or phenolic compounds can be used to effectively clean stalls and equipment used with these foals.

Salmonellosis

Infection with Salmonella spp can cause diarrhea in horses of any age. It is found in a low percentage (<1%) of normal horses and should therefore be considered a primary pathogen in foals with diarrhea. Foals can show varying degrees of disease severity depending on the serotype involved, but hemorrhagic diarrhea can be observed. Secondary infections in joints or bone are possible and may contribute to a poorer prognosis than is realized with many of the other listed causes.

Clostridium difficile

Clostridium difficile infection can be a cause of diarrhea in foals of any age, but this organism may also be found in the feces of healthy foals that are free of abnormal clinical signs. Unlike the situation in adult horses, C difficile infections in foals are not directly associated with antimicrobial administration. Enzyme-linked immunosorbent assay test kits can be used at veterinary hospitals to evaluate for this pathogen, making rapid diagnosis possible. Unlike many other causes of diarrhea, a specific treatment for this disease (metronidazole) is available and effective.

Clostridium perfringens

Clostridium perfringens (particularly type C) infection of the intestinal tract can induce severe disease that can result in death before treatment is even started, and mortality rates may exceed 50%. Severely affected foals are often young (<5 days) and may have hemorrhagic diarrhea. Treatment with metronidazole should be started immediately in foals suspicious for having this pathogen, before testing results are returned.

Coronavirus

Coronavirus has been reported in sporadic cases of foal diarrhea. Its role as a primary pathogen in horses remains unclear, and it has been identified in conjunction with other causes of foal diarrhea. A positive test result for coronavirus should be interpreted carefully unless all other causes have been excluded.

Cryptosporidium Species

Cryptosporidium parvum infection is an uncommon cause of diarrhea in foals but may affect individuals between 4 and 20 days of age. It has been described in individual cases and in herd outbreaks. Similar to other infectious causes, infectious disease control measures are extremely important in the management of this disease.

Parasites

Strongyloides westeri can cause mild diarrhea in foals between 1 and 2 weeks of age. Identification of large numbers (>2000 eggs per gram) of embryonated eggs in a fecal sample and exclusion of other causes of diarrhea are diagnostic for infection with this pathogen. Treatment of the mare with ivermectin 2 to 4 weeks before parturition can prevent transmission to the foal.

Initial Treatment

Treatment of foals with diarrhea is often initiated before a specific diagnosis is made because some confirmatory testing may take 48 to 72 hours or longer to complete. The clinical examination and laboratory work, if available, can be used to evaluate the immediate need for treatment while additional test results are pending. Healthy foals may require little treatment, whereas a severely compromised foal may need aggressive resuscitation.

Healthy Foal with Diarrhea

Foals categorized as otherwise healthy may not require treatment. They are often the foals with “foal-heat” diarrhea, but they may also have other causes of diarrhea and only mild clinical disease. A simple approach to these foals is to recommend frequent observation and monitoring by the owners (every 6 hours), which should specifically include taking of the body temperature and making note of nursing frequency. Additionally, administration of a smectite paste (Table 173-2 ) may help reduce the volume of diarrhea.

TABLE 173-2.

Dosages of Medications Used in Foals With Diarrhea

Medication	Dosage
Ceftiofur	5-10 mg/kg, IV, q 12-24 hr
Amikacin	20-25 mg/kg, IV, q 24 hr
Metronidazole	10-15 mg/kg, PO or IV, q 8-12 hr
Smectite paste	30-60 mL, PO, q 6-12 hr for a 50-kg foal
Lactase	6000 IU, PO, q 4-8 hr
Ivermectin	200 µg/kg, PO, once
Omeprazole	4 mg/kg, PO, q 24 hr
Flunixin meglumine	0.5 mg/kg, PO or IV, q 12-24 hr

Stable Foal With Clinical Abnormalities

A foal with diarrhea and fever that otherwise is hemodynamically stable (i.e., is drinking water or nursing and does not have clinically significant dehydration) also warrants close monitoring and may benefit from antidiarrheal medications as described earlier. In addition, beginning treatment for infectious diseases while testing is pending is often warranted, specifically the following:

• •Broad-spectrum antimicrobials, including ceftiofur, aminoglycosides, and metronidazole
• •Antiulcer medications
• •Nonsteroidal antiinflammatory drugs (low-dose)
• •Lactase enzyme
• •Smectite paste

Compromised Foal With Unstable Cardiovascular Status

A foal that has diarrhea and signs of the systemic inflammatory response syndrome (SIRS), as well as signs of hypovolemia (tachycardia, poor pulse quality, cool extremities, pale mucous membranes, prolonged capillary refill time, and depressed mentation), should receive medical treatment. In addition to the medications listed for foals in category 2 (stable foal with clinical abnormalities), intravenous fluid therapy is the most important and life-saving measure in this situation. An isotonic crystalloid with an electrolyte composition similar to normal foal values is ideal. Normosol-R1 (or Plasmalyte A2) represents a safe choice for administration in the absence of laboratory values. It has a higher sodium-to-chloride ratio, compared with many of the other fluids, making it more ideal for foals that have had significant fecal sodium losses. A fluid bolus of 20 mL/kg should be administered rapidly (over 20 to 30 minutes, if possible), followed by reassessment of the foal. If perfusion indicators have not improved, the bolus can be repeated for two additional doses (60 mL/kg total) if needed to help normalize perfusion.

Following these initial boluses of fluids, the foal can usually be changed to a slower and continuous rate of fluid administration. Depending on the age of the foal and severity of disease, a rate of 3 to 6 mL/kg per hour is often used. Replacement fluids (i.e., Normosol-R) are often still used for this phase of fluid therapy because they are higher in sodium than maintenance fluids, and ongoing sodium losses can be substantial in affected foals. Urine production and, ideally, body weight should be monitored to ensure that the foal is not becoming fluid overloaded. Many foals with diarrhea develop metabolic acidosis secondary to severe losses of sodium and bicarbonate. Although it is not likely appropriate for bolus administration, isotonic sodium bicarbonate can be made by adding sodium bicarbonate to sterile water to create a fluid with a tonicity similar to plasma. This can be used in diarrheic foals that have ongoing sodium losses, but potassium and calcium are often also required as fluid additives.

Given that foals with diarrhea may have gastrointestinal protein losses, colloids (typically plasma or hetastarch) are often considered as part of treatment. The higher oncotic pressure of these fluids makes them appealing for use in patients that have low plasma oncotic pressure. However, foals with diarrhea may be very prone to fluid overload for reasons other than low plasma protein. They can be expected to have changes in vascular permeability and the interstitial matrix. Although colloids may improve plasma oncotic pressure, they may still potentiate edema by increasing intravascular pressure or leaking into the interstitium. There is little clinical evidence in any species that colloids improve mortality rates despite their theoretical benefits.

Foals with abdominal pain from intestinal inflammation or gas distension may need more intensive pain management. The author has used lidocaine as a continuous intravenous infusion (0.05 mg/kg per minute) in foals with enteritis and diarrhea and has observed an improved comfort level. There is little research, however, describing the pharmacokinetics of this drug in foals. Other medications such as butorphanol or xylazine can also be used but may have less ideal secondary effects.

Foals with diarrhea that are colicky and gas-distended often need feed restriction to enable the colic and intestinal inflammation to subside. Application of a muzzle can be useful for preventing nursing, or the foal can be separated into a box or stall next to the mare. Parenteral nutrition or dextrose may be required in these cases if the foal is intolerant of nursing for an extended period.