Fallibility of faecal consistency as a criterion of success in the evaluation of oral fluid therapy for calf diarrhoea.

It is often said that the success of oral rehydration in humans depends on the adequacy of the improvement in the composition and volume of extracellular fluid, not reduction of faecal output. Indeed, the latter may increase initially. Such increases do not prevent the treatment from being effective but they may, falsely, undermine its acceptability to patients or those caring for them. This paper provides data to show that standard oral rehydration solutions used to treat experimentally induced calf diarrhoea procure identical improvements in plasma volume during the first 48 h, whether faeces improve or not, and those calves whose faecal consistency improved actually showed greater deterioration of extracellular fluid volume. While it is important for this to be appreciated by clinicians and explained to owners, it is absolutely imperative that those responsible for the approval of new therapeutic products for registration understand and accept that faecal consistency offers no reliable insight into the effectiveness of oral rehydration therapy for calf diarrhoea. It was, however, interesting that there was some relationship with correction of acidosis--perhaps because some of the contributing factors arise from colonic dysfunction.