Several case reports of Clostridium perjringens involvement in equine enteric disease have not identified the prevalence and statistical association of these bacteria with foal diarrhoea. Each of five methods which favoured the recovery of C. perjringens in different physiological states were chosen to improve the sensitivity of isolation in a survey of foal diarrhoea for C. perjringens and other pathogens. C. perjringens was significantly associated with foal diarrhoea (isolated from 57% of 421 scouring anjmals but from only 33% of 222 controls; odds ratio 7.4; p < 0.001 by multivariate analysis); it was also associated with fatal diarrhoea (odds ratio 2.7; p=0.047). Rotavirus, Cryptosporidium sp. and large numbers of Strongyloides westeri were the only other pathogens associated with diarrhoea although they were less prevalent than C. perjringens; Salmonella sp. was the only other pathogen associated with fatal diarrhoea. Enterotoxin production was detected by reverse passive latex agglutination test (RPLA) amongst isolates of C. perjringens from scouring and healthy foals. The enterotoxin gene from an equine strain was cloned and its sequence was essentially identical to that published for a human isolate. Less than 5% of C. perjringen isolated from scouring foals and 0.5% from controls were positive for the enterotoxin gene by polymerase chain reaction (PCR) (odds ratio 19.1; p<0.005). Presence of the enterotoxin gene was confirmed in representative isolates with a gene probe of chromosomal DNA and PCR product as well as neutralisation of cytotoxicity by antitoxin. Enterotoxigenicity of half ofRPLA positive isolates could not be confirmed in this way. Enterotoxigenic C. perfringens were a probable cause of foal diarrhoea. However, a greater proportion of the disease was associated with nonenterotoxigenic . perjringens. There is now a need to identify molecular differences between non-enterotoxigenic C. perjringens strains from scouring and healthy foals which might be associated with pathogenicity.

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