Differential diagnosis of diarrhoea in lambs

WHILE the consistency of healthy sheep faeces varies from firm pellets to soft paste, depending on the dry matter and fibre content of the diet, the observation of fluid faeces and faecal staining of the wool in the perineal region is not normal and indicates the presence of diarrhoea. Diarrhoea is seen commonly in lambs of all ages and is significant because it is usually associated with suboptimal production. The important aetiological factors differ according to the lambs' age and management system. Furthermore, the presence of diarrhoea is often accompanied by other clinical signs within the flock and is not necessarily the primary problem. It often occurs with bacteraemia, parasitaemia, endotoxaemia and toxicosis, or is associated with dietary changes or nutritional imbalances. Small improvements in the productivity of individual animals can have a substantial effect on the economic performance of the flock as a whole. An accurate diagnosis is therefore vital to ensure the best management of the problem, and is based on relevant husbandry factors and disease history, age of the lambs affected, examination of the flock, clinical examination of selected individual animals, collection of appropriate samples for laboratory investigation and, in some cases, postmortem examination. This article describes the differential diagnosis of diarrhoea in lambs of different ages, and highlights the problem of anthelmintic resistance associated with parasitic gastroenteritis which is commonly encountered in weaned lambs.