A survey of horses with acute diarrhoea: diagnosis, assessment of the prognosis, and comparison of two antibiotic therapies

Twenty horses, ponies, and foals referred with acute diarrhoea were divided at random into two treatment groups. One group was treated intravenously with trimethoprim/ sulfadiazine and the other group with ampicillin/gentamicin. Both groups were given the same standardized symptomatic therapy. All animals were evaluated clinically and 5 variables (general impression, heart rate, rectal temperature, appetite, and consistency of the faeces) were estimated on a five point scale (0-4). Jugular blood samples were taken at admittance and at regular intervals for routine screening. Three blood variables (packed cell volume, white blood cell count, and base excess) were also classified in a 5-point scale. The 'diarrhoea prognosis index' was the total sum of the eight variables scaled. Faecal samples were cultured aerobically and examined for worm eggs and larvae. A definite diagnosis was only reached in 11 horses (55%). Salmonellosis and parasitic infections were the most common causes of the diarrhoea. Seven horses (35%), three from the ampicillin/gentamicin group and four from the trimethoprim/sulfadiazine group, died or were euthanized because of a poor prognosis. Only the packed cell volume differed significantly between horses that died and horses that survived. No single clinical or haematological/biochemical variable did forecast the prognosis for the individual patient reliably, nor did the 'diarrhoea prognosis index'. The only reliable indication for the outcome of an individual horse appeared to be the clinical response to treatment within 4 days. The clinical outcome of both treatment groups did not differ significantly. In conclusion, it was difficult to reach a specific diagnosis in these horses with diarrhoea. It was not possible to forecast the prognosis of an individual patient by a single variable or by a combination of variables. No significant differences were found between the two antibiotic treatment groups.