Diarrhoea in horses and foals:
reducing the ‘no diagnosis’ cases

Although we see many cases of diarrhoea in equines of all ages, the cause is often elusive and we have to apply general treatment regimes. The percentage of horses with diarrhoea in which a firm ante mortem diagnosis is made has been variably reported as between 10 and 20%. Although many cases may be undeterminable and perhaps related to dietary changes etc, there is increasing recognition that infectious agents and/or their associated toxins are of major pathogenic importance in equine diarrhoeas and there are several test procedures now available to improve our diagnostic rate and help select more targeted therapy and prevention strategies.

Causes: The ‘usual suspects’ include Rotavirus and Cryptosporidium in foals and Salmonella sp. in all age groups. Other pathogens of potentially major importance both in foals and adult horses include Aeromonas sp, Clostridium difficile and Clostridium perfringens.

Diagnosis: Of the bacterial pathogens Salmonella and Aeromonas sp identification is relatively straightforward and both can be grown with reasonable success on routine culture media. Intermittent shedding of salmonellae may lead to false negative results and repeat samples are always advisable. Successful culture of C. difficile and C. perfringens is difficult and not diagnostic per se as not all strains are toxigenic. Hence the preferred approach to diagnosis of Clostridial diarrhoeas is ELISA identification of toxins – tests are available for C. perfringens enterotoxin (CPE) and C. difficile toxins A and B (TOX A/B). Detection of both Rotavirus and Cryptosporidium in cases of foal diarrhoea also requires an immunological technique – namely immunochromatography (ICT). All of these tests (see over) can be easily performed on a small sample of faeces.

(* all tests performed on faecal samples; # based on only one publication)

Treatment: The use of antibiotics in bacterial diarrhoeas has always been a contentious issue but is less contentious when a specific agent has been identified for which a suitable antibiotic can be targeted. For example, metronidazole is effective against the vast majority of Clostridial enteropathogens and enrofloxacin is effective against the vast majority of Salmonellae and Aeromonads. Codeine phosphate is an old and reliable means of halting diarrhoea with typically 1-2 mg/kg bid per os being effective in most cases or up to 3 mg/kg tid in the more severe cases (NB. a slow withdrawal of treatment is vital to success). As an alternative loperamide (‘Imodium’) can be used at 0.1-0.2 mg/kg bid per os (2-5 capsules bid per 50kg foal). Adsorbents such as bismuth subsalicylate (‘Pepto-bismol’) at 1 ml/kg bid per os is a useful adjunct to acute diarrhoea in horses and foals and some cases benefit from therapy to counter bowel oedema including corticosteroids and hetastarch.