In a randomized block design experiment, the effect of fecal inocula from horses supplemented with live yeast (Saccharomyces cerevisiae) in diets containing 50% oat straw on in vitro total gas (gas production [GP]), methane (CH4), and carbon dioxide (CO2) productions as indicators of hindgut activity was assessed. Three commercial products of S. cerevisiae were tested (1) Biocell F53 (YST53), (2) Procreatin 7 (YST07), and (3) Biosaf SC47 (YST047). For the incubations, each product was added at 0 (control without yeast addition), 2, or 4 mg/g dry matter (DM). Fecal inocula for incubations with each treatment was obtained from Quarter Horse mares fed the same yeast additives for 15 days, resulting in four different fecal inocula (FI53, FI07, FI47, and FI00). The fecal content mixed with the culture media were used to inoculate three identical runs of incubation in bottles containing 1-g DM of substrate (a mixture of concentrate and oat straw [1: 1 DM]). The GP, CH4, and CO2 productions were measured at 2, 4, 6, 8, 10, 12, 24, and 48 hours post-incubation. Addition of additives YST53 and YST07 at 2 mg/g DM resulted in higher asymptotic GP (linear effect, P = .021) and GP during the first 12 hours of incubation (linear effect, P < .05) compared with control without yeast addition, with the highest value being for the dose 2 mg/g DM with the fecal inoculum FI53. The additive YST47 at all doses with fecal inoculum FI47 had lower GP (linear effect, P < .05) at different incubation hours compared with control. The additive YST53 increased GP, CH4, and fermentation kinetics at the dose 2 mg/g DM with decreasing CH4 production by 78% at 4 mg/g DM at 24 hours of incubation. Addition of YST53 at 2 and 4 mg/g DM with fecal inoculum FI53 enhanced fermentation kinetics (P < .05) compared with control and other additives at different doses. It can be concluded that the yeast additive Biocell F53 was the most effective at doses of 2 and 4 mg/g DM compared with other Saccharomyces strains to attain a more favorable hindgut fermentation to digest fibrous roughages by horses. (C) 2016 Elsevier Inc. All rights reserved.

Authors thank Universidad Autónoma del Estado de México for financial support of the project #3706/2014 CID. Kholif A.E. thanks the National Council for Science and Technology (CONACyT, Mexico) and The World Academy of Sciences (TWAS, Italy) for his postdoctoral fellowship at the Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma del Estado de México, México.

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