INFLUENCE OF SACCHAROMYCES CEREVISIAE ON THE ENVIRONMENTAL EFFICIENCY OF METHANE PRODUCTION IN DAIRY AND BEEF CATTLE: META-ANALYSIS

The use of feed additives (e.g. yeasts products) for reduction of ruminants’ methane (CH4) production has drawn the attention of cattle nutritionists and environmentalists. Although there are many relevant studies on this topic, but the obtained results for dairy and beef cattle are contradictory. Therefore, the objective of the present study is to examine the effect of yeast (Saccharomyces cerevisiae) on reduction of CH4 production in dairy and beef cattle using meta-analytic methods. After compilation of relevant articles published between 1990 and 2016 and applying exclusion and inclusion criteria, meta-analyses of data from dairy and beef cattle were applied for the pooled dataset or for each animal category (dairy or beef). The effect size of yeast on CH4 production (g/day) and CH4 production per dry matter intake (CH4/DMI (g/kg)) was estimated as standardized mean difference at 95% confidence interval. In addition, heterogeneity across studies was tested by using Q test and I2 index. Study bias was verified through Funnel plot and trim-and-fill method. The results of meta-analysis of all 3 groups of animals (all cattle, dairy cattle, and beef cattle) suggested that effect size of yeast on CH4 production (g/day) and CH4/DMI (g/kg) was not significant. In other words, the use of yeast for dairy and beef cattle did not reduce CH4 production and CH4/DMI (g/kg) significantly. The results of Q test and I2 index suggest that there is no heterogeneity between different studies on CH4 production and CH4/DMI (g/kg) so that value of I2 index of CH4/DMI (g/kg) in dairy and beef cattle was about 14% while for dairy cattle, the index is about 40%. There was no study bias of CH4 production as well as CH4/DMI (g/kg). As shown in funnel plot, the studies are more concentrated in the lowest part of the plot. The results of meta-analysis suggest that use of yeast (Saccharomyces cerevisiae) as feed additive does not offer significant results in terms of reduction of CH4 production in dairy and beef cattle. It is recommended to conduct further studies on effect of different doses of yeast, use of yeast products, different strains and experimental designs