Diagnosing salmonellosis in horses. Culturing of multiple versus single faecal samples

Three rectal faecal samples were taken at 24-hour intervals from 136 horses in order to investigate whether multiple faecal cultures yield a greater number of Salmonella-positive horses compared to single faecal cultures. Of these 136 horses, 89 were suspected of salmonellosis on clinical grounds and 47 belonged to a control group. From the 'Salmonella suspected' group, 22 horses (25%) were Salmonella positive on one or more occasions. Only twelve of these 22 positive horses (55%) were positive at first sampling. Of the control group, only three horses (6%) were positive for Salmonella. Thirty-one (69%) of the 45 positive cultures from the 'Salmonella suspected' group were found only after enrichment in Selenite broth. From the results of the present study it is concluded that multiple faecal cultures are superior to single faecal cultures for diagnosing clinical salmonellosis in horses and that there is no relation between the course of the disease and whether the Salmonellae were cultured directly or indirectly, after enrichment in Selenite broth. Salmonellae were cultured from the faeces of horses treated with antibiotics before their referral, even when the isolated strain was sensitive to the antimicrobial drug used by the practitioner.