Feed restriction enhances the depressive effects of erythromycin on equine hindgut microbial metabolism in vitro.

Equine typholocolitis is a sporadic diarrheal disease causing high mortality rates. One of the risk factors responsible for this is the oral application of the macrolide antibiotic erythromycin. The aim of the present in vitro study was to investigate whether erythromycin in combination with feed restriction provokes changes in microbial hindgut metabolism and could therefore be involved in the pathogenesis of equine typhlocolitis. As application of erythromycin and feed restriction are risk factors for equine typhlocolitis, both factors were chosen to investigate their individual and combined effects on hindgut microbial metabolism. The colon simulation technique (Cositec) was used to evaluate biochemical parameters of microbial metabolism. Production rates of the acetate, proprionate and butyrate were measured as quantitative parameters of microbial fermentation. Application of erythromycin (10 mg/d) predominantly decreased the production rates of propionate. Reducing the fermentable substrate to 30% induced an even more pronounced impairment. The detrimental effects of feed restriction on the production rates of short-chain fatty acids (SCFA) were enhanced when feed restriction was combined with the application of erythromycin. Irrespective of erytrhomycin, the butyrate fermentation rate was completely inhibited by feed restriction within two days after start of restriction. The reduction in butyrate fermentation rate has to be discussed as a pathophysiological factor for the onset of acute typhlocolitis.