In order to evaluate the effect of using probiotic (Saccharomyces cerevisiae) in diets for horses, it was used four male equines, with average body weight of 400 kg, in a 4 õ 4 Latin square design. Diets were composed of concentrated and 85 Tifton grass hay (low quality) or alfafa hay (high quality), with or without addition of yeast. Each experimental period lasted 36 days, with total fecal collection for determination of apparent digestibility coefficients of the nutrients and fecal collection for determining pH and fecal microbiology. Use of probiotic did not affect apparent digestibility coefficients of the diets, except for ether extract. Hay nutritional quality affected coefficients of dry matter digestibility, crude protein and ether extract (EE) only for diets with Tifton grass hay without probiotic and with alfafa hay with probiotic. The utilization of yeast culture increased the Lactobacillus population in feces of animals fed diet with Tifton grass hay with probiotic. Probiotic was not used in population of Lactobacillus in diets of alfafa hay (good quality). Streptococcus population in the diet increased as yeast was supplemented in both diets with Tifton grass hay as that with alfafa hay. Diet with 85 Tifton grass without probiotic promoted reduction in fecal pH values 14 and 17 hours after feeding. Considering the values of fecal pH in this periods after feeding, the diets supplemented with probiotic showed values higher than those without addition of yeast.
apparent digestibility; feces; horses; microbiology; probiotic; roughage
