Fecal Gas Production of Ten Common Horse Feeds Supplemented With Saccharomyces cerevisiae

• Yeast addition increased the asymptotic GP of concentrates compared to forage feeds.
• Concentrate feeds had higher GP and lower rate of GP compared to forages.
• Forages increased ruminal pH compared to concentrates, and decreased ME.
• Yeast increased fermentation kinetics of steam-rolled barley, wheat bran, and corn stover.

The study aimed to assess the nutritive value of 10 feeds (grains and forages) commonly used in horse nutrition in Mexico, on the basis of their chemical composition, in vitro organic matter digestibility (IVOMD) and in vitro gas production measurements with or without the supplementation of Saccharomyces cerevisiae (SC) 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. Substrates tested were: 6 concentrates (corn gluten meal, soybean meal, steam-rolled corn, steam-rolled barley, oat grain, and wheat bran) and 4 roughages (soybean hulls, corn stover, alfalfa hay, and oat hay). Gas production (GP) was recorded at 2, 4, 6, 8, 10, 12, 14, 24, 48, and 70 hours using the pressure transducer technique. Some ingredient × yeast interactions were observed (P ≤ .020) for the asymptotic GP and GP at 48 and 70 hours of incubation. Yeast addition increased (P < .001) the asymptotic GP of concentrates compared to roughages. Concentrate feeds had higher (P < .05) GP and lower (P < .001) rate of GP compared to roughages without yeast. From 24 to 70 hours of incubation, forages with or without yeast had lower (P < .05) GP compared to concentrates supplemented with SC. Forages had higher fermentation pH compared to concentrates but lower (P < .05) metabolizable energy, IVOMD, and microbial protein production compared to concentrates. Supplementation with SC increased (P < .05) the asymptotic GP of oat grain, soybean meal, soybean meal, steam-rolled barley, steam-rolled corn, wheat bran, corn stover, and oat hay, without affecting the rate of GP or lag time of oat grain, soybean meal, wheat bran, corn stover, and oat hay. Moreover, supplementation with SC increased (P < .05) metabolizable energy, IVOMD, and microbial protein production of steam-rolled barley, wheat bran, and corn stover, without affecting (P > .05) the fermentation of other feeds. Supplementation with SC improved fermentation of feeds with higher effects on concentrates compared to roughages. It was concluded that although SC mainly improves concentrate utilization by horses, it also improves fiber digestion when used on high-roughage diets fed to horses.