Table 1.

Observations from different articles reporting effects of yeast on rumen microorganisms and functions.

Title of research	Treatment/Dosage/System	Observations and summary	Authors
Effects of Saccharomyces cerevisiae at direct addition or pre-incubation on in vitro gas production kinetics and degradability of four fibrous feeds	Varying doses of yeast (S. cerevisiae) incubated with corn stover, oat straw, sugarcane bagasse and sorghum straw (in vitro)	•Direct addition or 72 h pre-incubation of S. cerevisiae with corn stover and oat straw improved gas production. •Direct addition or 72 h pre-incubation of S. cerevisiae to sorghum straw increased asymptotic gas production, the rate of gas production, and initial delay before gas production begins, DM and NDF digestibility. •Improve ruminal fermentation of low quality forages at 4 to 12 g/kg DM because gas production depends on nutrient availability for rumen microorganisms.	Elghandour et al. (2014)
Effects of Saccharomyces cerevisiae fermentation product on in vitro fermentation and microbial communities of low-quality forages and mixed diets	S. cerevisiae fermentation/concentrations of 0, 1, 2, 3 g/L (in vitro)	•The molar proportion of acetate and propionate respectively increased linearly with an increasing amount of S. cerevisiae for RS, CS, and CSNG. •Microbial protein increased linearly with an increasing level of S. cerevisiae for RS, and it reached peak values at 1 and 2 g/L S. cerevisiae for CSG and CSNG, respectively. •Fungi population was increased with 1 g/L S. cerevisiae for all forages except CSNG. The population of Ruminococcus flavefaciens increased at 1 or 2 g/L S. cerevisiae for RS, CSNG, and CSG. Total VFA reached a peak at 1 g/L S. cerevisiae for RS, CSNG, and CSG and increased for CS. •It is inferred that the addition of S. cerevisiae could improve the rumen fermentation of forages by stimulating the number of fibre-digesting rumen microbes, especially fungi populations.	Mao et al. (2014)
Effect of yeast culture (Saccharomyces cerevisiae) on the ruminal microbial population in buffalo bulls	Yeast culture (in vivo)	•A significant increase in the mean protozoal count (by 3.0 × 104 per mL) and the total bacterial count (by about 4.0 × 104 per mL) as compared with the control group.	Kumar et al. (2013)

DM = dry matter; NDF = neutral detergent fibre; RS = rice straw; CS = corn silage; CSNG = corn silage without grain; CSG = corn silage with grains; VFA = volatile fatty acid.