EFFECTS OF DIET AND HINDGUT DEFAUNATION ON DIET DIGESTIBILITY AND MICROBIAL CONCENTRATIONS IN THE CECUM AND COLON OF THE HORSE

The effects of diet and hindgut defaunation (removal of protozoa from the hindgut) on diet digestibility (Trial 1) and on total and cellulol ytic bacterial and fungal concentrations in the cecum and colon (Trial 2) were investigated. A high-forage (HF) diet, 90% alfalfa hay-10% co ncentrate, or a higher-concentrate (HC) diet, 60% alfalfa hay-40% conc entrate, was limit-fed. In Trial 1, defaunation resulted in a slight d ecrease in DM digestibility (P < .1) and had no effect on cellulose di gestibility. Dry matter digestibility was higher (P < .001) with the H C diet; however, no differences were observed in cellulose digestion. For the faunated periods, protozoal concentrations were similar in the cecum and greater in the colon for both diets (P < .05). A diet x loc ation interaction was observed for the genera Buetschlia and Blepharor orys. In Trial 2, defaunation had no effect on either total or cellulo lytic bacterial concentrations in the cecum or colon. Total bacterial concentrations were higher (P < .06) in the colon when ponies were fed the HC diet. Defaunation did not affect total fungal concentrations i n the cecum; however, fungal concentrations in the colon were slightly higher (P < .1) when the ponies were defaunated. Diet had no effect o n total or cellulolytic fungal concentrations. Both total and cellulol ytic fungal concentrations were approximately 10-fold higher in the co lon than in the cecum (P < .01). Protozoa do not seem to play an essen tial role in the fermentation of feedstuffs in the equine hindgut.