ABSTRACT: The study aimed to assess the nutritive value in vitro of 4 feeds (grains and forages) commonly used in horses nutrition in Mexico, in the absence or presence of Saccharomyces cerevisiae at 4 mg/g DM. Fecal inoculum was obtained from 4 adult English
Thoroughbred horses fed on restricted amount of concentrate and oat hay ad libitum. The
incubated substrates included were corn gluten meal, soybean meal, oat grain and alfalfa hay. Gas production was recorded at 2, 4, 6, 8, 10, 12, 14, 24, 48 and 70 h using the Pressure
Transducer Technique. Some ingredient × yeast interactions were observed (P < .020) for the
asymptotic gas production (GP) and GP at 48 and 70 h of incubation. Yeast addition increased (P
< .001) the asymptotic GP of concentrates compared to forages. Concentrate feeds had higher (P
< .05) GP and lower (P < .001) rate of GP compared to forages without yeast. From 24 to 70 h
of incubation, forages with or without yeast had lower (P < .05) GP compared to concentrates
with yeast addition. Forages had higher fermentation pH compared to concentrates, but lower (P
< .05) metabolizable energy (ME), in vitro organic matter digestibility (IVOMD) and microbial
protein production (MBP) compared to concentrates. Yeast addition increased (P < .05) the
asymptotic GP of oat grain and soybean meal, without affecting the rate of GP or lag time of
both. Yeast treatment improved fermentation of feeds with higher effects on concentrates
compared to forage. It was concluded that concentrate feeds had higher nutritive value than
forages commonly fed to horse
