Diarrhea

I. Foal Heat Diarrhea

1. Most frequently occurs at a time that would correspond with dam's first postpartum estrus; foal is 6-10 days old.
2. Foals are bright and alert.
3. Duration is usually 2-5 days.
4. Usually no therapy required other than perineum cleaning.

II. Nutritional

1. Consumption of excessive amount of milk after a foal is separated from its dam for a period of time, or in overfeeding ill or orphaned foals.
2. Sudden changes in diet of the mare or foal.
3. Foreign material (sand, dirt): Examine feces for sand, digital exam of rectal mucosa for grit.
4. Carbohydrate intolerance. While primary carbohydrate intolerances are uncommon, they are often transient and associated with viral diarrhea.

III. Parasites

1. Strongyloides westeri [1]

1. May cause diarrhea in foals at 1-4 weeks of age.
2. Larvae in mare's milk beginning at 4 days postpartum and peak at 10-12 days.
3. Prepatent period in foal 6-14 days; - Use fresh feces and sugar flotation.
4. Treatment with thiabendazole, cambendazole, ivermectin.
5. Administering ivermectin to mares on day of parturition prevents transmission to foals.

2. Parascaris equorum. Heaviest infections of P. equorum occur in late suckling or weanling foals. Diarrhea is unlikely manifestation.
3. Crytosporidium sp. [2,3]

1. Associated with diarrhea in both immunocompetent and immunosuppressed foals.
2. Incubation 9-28 days.
3. Oocysts found in feces by sugar float or direct FA test (FA is the best test) [3].
4. Found in 15-31% of normal foals beginning at 4 weeks; very rare in yearlings and adults [3].
5. Duration of excretion of oocysts can be up to 14 weeks.
6. Infected foals considered the source of infection for other foals.

4. Giardia [3]

1. Found in 17-35% of foals in one study; all age groups including nursing mares.
2. Foals shed cysts between 2 and 22 weeks of age.
3. May be concurrently infected with cryptosporidium.
4. Infected mares considered the source for foals.
5. Relationship to diarrhea in most cases is not observed.

IV. Bacteria

In a retrospective study at University of Florida, at least 1 infectious agent was detected in 122/223 (55%) foals. Rotavirus was most frequently isolated (20%), followed by C. perfringens (18%), Salmonella spp. (12%), and C. difficile (5%). The survival rate was 87% (191/223) [4].

1. E. coli is a frequent cause of septicemia in which diarrhea may be a component; however, E. coli has not been frequently documented as a primary cause of foal diarrhea. Effacing E. coli can cause bloody diarrhea.
2. Salmonella spp. endotoxemia/diarrhea. (See Neonatal Salmonellosis)
3. Clostridium perfringens type C, has been responsible for high mortality in neonatal foals during the first two days of life. These organisms have been isolated from the gut in large numbers from foals with a necrotizing hemorrhagic enteritis characterized by colic, depression, hemorrhagic diarrhea, shock and death; however, peracute cases may manifest as sudden death without diarrhea.

1. Produces hemorrhagic necrotizing enteritis characterized by colic, depression, shock and death in 12 hr - 4 day old foals. It may manifest as sudden death without diarrhea.
2. May affect more than 1 foal on a farm, causes illness in newborn foals within 72 hours of birth. Changing foaling environment and hygiene usually not successful.
3. Clinical pathology - Leukopenia, neutropenia, ≥ azotemia, metabolic acidosis.
4. Therapy of ill foals consists of supportive care (IV fluids, acid-base) IV antibiotics because gut is often eroded and may have concurrent gram-negative bacteremia, IV Clostridium perfringens type C & D antiserum, no milk for 24 hours, IV and oral plasma, oral metronidazole.
5. Diagnosis via pathology - Hemorrhagic necrotizing enteritis, large number of gram-positive rods, Clostridium perfringens α and β toxin in fresh gut contents.
6. Editor's Comment - In outbreaks on a farm try this: wash mares udder and remove smegma and dirt between sides of mammary gland, disinfect, lessen caloric intake of mare to reduce milk, milk out 1 side of mammary gland to lessen foals milk intake, oral metronidazole at 10 mg/kg BID beginning at 8-12 hours of age (Editor's Comment - No sooner because of open gut) for 5 days may prevent disease. Use C. perfringens antitoxin orally during first 6 hrs of life.

4. Clostridium difficile

1. In foals < 3 days of age; two presentations:

1. Fatal hemorrhagic necrotizing enterocolitis [5]
2. Severe watery diarrhea [6]

2. Diagnosis by fecal culture (direct plating of fecal specimen in selective media) or cytotoxin via assay

1. Submit 25-50 ml of liquid feces
2. Must evaluate within 24 hours - Keep refrigerated or freeze

3. Therapy with metronidazole may be beneficial if administered early

5. Necrotizing enterocolitis [7]

1. Associated with high risk and premature foals.
2. Clinical signs seen at 3-24 hours of age are abdominal distension and ileus, colic and signs of septicemia.

1. Foals are acidotic, hypotensive.

3. Diagnosis via abdominal radiographs for pneumatosis intestinalis.
4. Therapy is ICU support, parenteral nutrition, ≥ surgical removal of affected bowel.

6. Rhodococcus equi. Occasionally causes diarrhea in foals between 1 and 4 months of age, but has not been a neonatal problem.
7. Actinobacillus equuli. Diarrhea attributed to the organism is frequently a secondary manifestation of septicemia in the neonate from birth to 2 weeks of age.

V. Viruses

1. Rotavirus

1. Epidemiology [8]

1. Affects ages 2 days to 4-5 months.
2. Younger foals more severely affected.
3. Outbreaks of rapid spreading diarrhea reported.
4. Low mortality, high morbidity.
5. 1/3 of foals positive for rotavirus are asymptomatic.
6. Phenolic disinfectants required to disinfect. (Bleach not effective).
7. Recovered foals shed virus for 4-10 days following recovery and can perpetuate spread of infection during that time.
8. Virus persists in environment for up to 9 months.

1. Control is sanitation, isolation and quarantine of affected premises, protective clothing, team effort.

1. Diagnosis [8]

1. Virogen Rotatest® (Wampole Laboratories) rapid detection of rotavirus antigen in feces.

1. Elisa test is sensitive and specific.
2. Clinical signs should be compatible.

2. Clinical Signs [8]

1. Fever, depression, watery diarrhea, ≥ anorexia.
2. Younger foals more severely affected.
3. Dehydration, electrolyte and acid-base problems.
4. Synergistic infection with other agents may potentiate severity of clinical signs [9]
5. CBC usually normal except for evidence of dehydration.

3. Prevention

1. Immunity is based on local gut immunity.
   Vaccine for horses - Administer to pregnant mares. Fort Dodge Laboratories, PO Box 518, Fort Dodge, Iowa 50501, www.fortdodge.com [10]
2. Minimize stress and crowding, isolate diarrhea cases.

2. Other viruses [8]

1. Corona virus isolated from foals with and without diarrhea; significance is unknown.
2. Adenovirus isolated from diarrheic foal, significance unknown.

3. Immunodeficiency

1. Regardless of the type of deficiency (i.e., failure of passive transfer, combined immunodeficiency, humoral immune system abnormalities, cellular immune system abnormalities, etc.) such immunocompromised foals are more susceptible to all infections and diarrhea is a common manifestation.

VI. Some Orally and Systemically-Administered Antibiotics

Some orally and systemically-administered antibiotics (e.g., oxytetracycline, erythromycin, rifampin, trimethoprim-sulfa, ampicillin) have been incriminated as causal agents of diarrhea due to toxic effects, alterations in normal intestinal flora, superinfections by pathogens (Clostridium difficile), and the emergence of resistant strains of bacteria.

VII. Evaluation

1. History. Particular attention must be paid to the age of the affected foal because of the age of occurrence of some etiologic types of diarrhea, i.e., foal heat diarrhea, enterotoxemia, etc.
2. Physical examination.
3. Overeating confirmed by:

1. History
2. Acid fecal pH
3. Presence of reducing sugars in feces (Clinitest®, Ames Co., Division Miles Laboratories, Elkharter, IN.)

4. Carbohydrate intolerance

1. Lactose tolerance test. (See absorption tests)
2. Response to treatment with lactase preparation (Lact-Aid® Lactaid Inc., Pleasantville, NJ).

5. Blood

1. Blood cultures in suspect neonatal septicemia. Most bacteremias are gram-negative and yield more than one isolate.
2. Complete blood count.

1. Leukopenia associated with Salmonellosis, E. coli septicemia, Clostridia sp., endotoxemia.
2. May be unremarkable in viral diarrheas.

3. Electrolytes

1. Diarrhea causes losses of sodium, bicarbonate, chloride, potassium and calcium.

4. BUN, creatinine, may be elevated due to hemodynamic (pre-renal) nephritis from infectious agents, or tubular damage from concurrent use of aminoglycoside antibiotics.
5. IgG - Often is low (< 400 mg/dl)
6. Acid/base status.

1. Can be determined by measuring total CO2 with Harleco® CO2 Apparatus.
2. Milliequivalent of bicarbonate needed = base excess X body weight (Kg) X 0.4.

6. Hydration

1. Indicators of dehydration include poor jugular distensibility; enophthalmos, increased skin turgor, prolonged CRT, and elevated HCT & TPP.

7. Absorption studies

1. Oral lactose tolerance test to determine diarrhea attributed to maldigestion.

1. 1 gram lactose/kg body weight as a 20% solution via nasogastric tube.
2. Curve normally peaks at 90 minutes following lactose administration.
3. Normal: should see ≥ 35 mg/dl 92 mmol/l) increase in blood glucose

VIII. Therapy

1. Foal Heat diarrhea

1. Uncomplicated cases require no specific therapy other than cleansing of the foal's perineum and subsequent application of a water repellent ointment to prevent scalding and hair loss.

2. Lactose-intolerant foals should have limited access to mare's milk.

1. Mare's milk can be "stripped" or foal can be muzzled. Foal may be given commercial milk replacer with yeast-derived lactase enzyme (Lactaid®, SugarLo Co., Pleasantville, NJ).

3. Parasites

1. Strongyloides westeri. Benzimidazoles are effective against adults in small intestine.
   Thiabendazole (44 mg/kg); cambendazole (20 mg/kg); oxibendazole (10 mg/kg).

4. Fluids in light of the consequences of dehydration and electrolyte imbalances (See Fluid and Electrolyte Balance). Fluid and electrolyte replacement and maintenance should be of utmost concern. Fluids with sodium chloride, bicarbonate and potassium replacement can be accomplished by oral or intravenous therapy.

1. Commercially available glucose-electrolyte supplements can be administered free-choice to diarrheic foals that are able to drink from a bucket; otherwise, they can be administered via nasogastric tube.

1. Withhold milk from foal while administering oral fluids.
2. Monitor plasma glucose closely and supplement as needed. These preparations will predispose to hypoglycemia if no other source of energy is available and should be used on a short-term basis.

2. I.V. fluid and electrolyte solutions should be isotonic as fluid loss is isotonic. (See Fluid and Electrolyte Balance).

5. Plasma Transfusion (See Plasma Therapy)

1. Indications

1. Failure of passive transfer in presence of diarrhea + septicemia.
2. Protein loss through inflamed bowel wall may lead to hypoproteinemia.

6. Antimicrobial Therapy (See Guidelines for Drug Use in Equine Neonates)

1. Indicated in the neonate with diarrhea and signs of depression and anorexia because they frequently become septicemic. Selection of appropriate antimicrobials should be based on blood culture and susceptibility results.

1. Rotavirus infected foals will not need antimicrobials if CBC is normal.

2. Be aware of enhanced nephrotoxic potential of aminoglycosides due to decreased renal perfusion in diarrheic, hypovolemic and dehydrated foals.

7. Internal Protectants

1. Bismuth subsalicylate. It also acts to neutralize bacterial toxins; 3-4 ounces/45 kg PO, every 6-8 hours.
2. Kaolin and pectin; 3-4 ounces/45 kg PO, every 23 hours.
3. Activated charcoal. It may act to neutralize toxins of some organisms, i.e., Salmonella spp., Clostridium spp., and E. coli. 0.5-1.0 oz (15-30 g)/45 kg, every 12 hours, via nasogastric tube.
4. Di-tri-octahedral smectite (Biosponge, Platinum Performance, Buellton, CA) can bind endotoxin and has been shown to neutralize toxins of C. difficile and C. perfringens. 15-30 ml every 6 hours

8. Intestinal lubricant/cathartic

1. Mineral oil. It may be used in managing overeating induced enteritis.
2. Mucilloid via stomach tube beneficial in managing sand-induced enteritis. 1-2 ounces mucilloid (Metamucil®, Searle and Co., San Juan, PR; Mucilose®, Winthrop-Breon Laboratories, New York, NY).

9. Nonsteroidal anti-inflammatory drugs (NSAID)

1. Caution must be exercised because of their potential nephrotoxicity and role in gastroduodenal ulceration.

1. Minimum effective dosage should be used.
2. Flunixin meglumine appears to be safer than phenylbutazone.

10. Total Parenteral Nutrition (TPN) should be considered along with making the severely diarrheic foal NPO if it is not so already (See Parenteral Nutrition & Enteral Nutrition).
11. Gastrointestinal ulcer prevention (See Gastroduodenal Ulcers)

IX. Epidemiology of Foal Diarrhea

1. Risk factors associated with increased incidence of foal diarrhea [11].

1. Shavings for stall bedding.
2. Prophylactic treatment of foals with antibiotics.
3. Treatment of foals with vitamins.
4. Foals born to non-farm resident mares.

2. Risk factors associated with decreased incidence of foal diarrhea [11].

1. Stall disinfection between foaling mares.
2. Tail wrapping and udder washing mares.
3. Use of straw for stall bedding.

3. Salmonella spp infections.

1. In foals <12 weeks of age Salmonella spp tend to be primary cause of death whereas in older animals Salmonella not correlated with lesions.
2. Serotypes include (from most common to least): S. typhimurium, S. typhimurium var copenhagen, S. saint-paul, S. kentucky, S. muenchen, S. montevideo, and many other serotypes.