C. Langdon Fielding
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.
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:
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.
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