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Foal Diarrhoea
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Introduction
Diarrhea is a significant cause of morbidity and mortality in the neonatal foal. Numerous noninfectious and infectious agents are responsible for enterocolitis and enteritis. This article provides an overview of the differential diagnoses for neonatal diarrhea and general and specific guidelines for therapy.
Many causes of diarrhoea result in abdominal pain before abnormal faeces are observed. Contagious causes of faol diarrhoea are spread by environmental-oral or faecal-oral transmission. In the equine neonate enteritis/diarrhoe is one of the signs of sepsis. The diagnosis can be difficult because the diagnostic methods have limitations. There are often important herd considerations as well as individual factors. Frequently, a potential pathogen is not identified. Radiography and ultrasonography are important diagnostic aids for evaluating foals with abdominal distension.
Diarrhoea can cause dehydration and significant acid-base and electrolyte imbalances in a very short period of time, especially in young foals. Early diagnosis and carefully considered treatment are important.
Mare and foal
Causes, diagnosis, therapy and prevention of foal diarrhoea
• Foal heat diarrhoea. This occurs most frequently at the time that corresponds with dam's first postpartum oestrus, and is probably related to the natural faunation that occurs in foals between 1 and 2 weeks of age. It is most likely caused by hypersecretion in the small intestinal mucosa, which may overwhelm an immature colon that is unable to compensate by increased fluid and electrolyte absorption.Usually no therapy is required. After cleaning the foal's perineum, a water repellent ointment can be used to prevent scalding and hair loss.
• Nutrional causes (overfeeding, sudden diet changes, foreign material). Overfeeding, failure to adhere to instructions for milk replacers and sudden diet changes of the mare and/or foal should be avoided. Eating foreign material (sand, etc.) should be prevented as this also may cause irritation of the gastrointestinal tract.
• Lactose intolerance. Primary lactose-intolerance from a congenital deficit or absence of lactase in the brush border of the small intestine is rare in foals but secondary lactose intolerance may occur after many small intestine infections as a result of the loss of lactase-producing intestinal cells. Supplementation with lactase (fresh yoghurt) may have a benificial effect.
• Viral intestinal disease (Rotavirus, Coronavirus). Rota-virus infection is probably the most common infectious cause of faol diarrhoea. The severity of the disease is determined by immune status, inoculation dose and the age of the foal. Adult carriers and infected foals may shed rotavirus, and the organisms may persist in the environment for up to 9 months. After oral infection the virus replicates the villous tips of the small intestine, and these cells are destroyed. The gut looses absorptive function and probably alos the ability to produce lactase. Fals may be anorectic, depressed and develop diarrhoea within 24h. Fever is not always present. Diagnosis can be made with a test on faeces. Foals should be kept on mare's milk, intravenous rehydration and electrolyte balancing may be needed.
• Helminth parasites. Strongyloides westeri may affect as may as 90% of young foals, but is usually non-symptomatic except when present in enormous numbers. Foals can acquire a patent infection as early as 8-12 days of age because transmission of larvae is transmammary or incidentally through penetration of the skin. Prevention is achieved through deworming the mare with ivermectin 1-2 weeks before the expected parturition date. Incidentally, haevy infection with Strongyle spp. may cause diarrhoea in older foals. Diagnosis may be difficult as faecal samples will be negative for eggs. Parascaris equorum is more commonly associated with intestinal obstructiopn than diarrhoea.
• Protozoan parasites (Cryptosporidium). The role of Cryptosporidium spp. in foal diarrhoea is controversial. Clinical infection in immunocompetent animals is slef-limiting, but fatal enterocolitis and chronic diarrhoea have been reported. Diagnosis is made by detecting oocysts in a faecal sample. Treatment is generally supportive.
• Anaerobic and aerobic bacterial pathogens (Clostridium, E. Coli, Salmonella, Rhodococcus equi). Clodstridium is an important cause of enteric disease in young foals as it may produce potent exotoxins that damage the mucosa and cause fluid loss into the gut lumen and peritonal cavity. Affected foals can develop severe colic with gas distension preceding the (haemorrhagic) diarrhoea or they may die acutely of shock. Treatment is often disappointing but should consist of fluid therapy and antimicrobial agents. Clostridium is often associated with stress, antibiotic-associated diarrhoea and hospital environments, and clinical signs range from mild diarrhoea to severe necrotising haemorrhagic enterocolitis.
E. Coli has rarely been associated with diarrhoea in foals, although it is the most common cause of septicaemie in newborn foals.
In foals, infection with Salmonella spp. mostly occurs as isolated cases. The mare appears to be the primary source of infection in most cases. Affected foals usually have moderate to severe clinical signs that include fever, diarrhoea, dehydration, profound depression and reduced appetite. The diagnosis is confirmed by faecul culture.
Rhodococcus equi usually causes respiratory problems, but occasionally infected foals may have acute or, more often, chronic diarrhoea.
• Gastric ulceration
• Antibiotic associated diarrhoea
