The Effects of Dietary Saponins on Ruminal Methane Production and Fermentation Parameters in Sheep: A Meta Analysis

Ruminants production systems are facing a critical period within global agriculture due to their unique digestive system which, whilst allowing them to utilize low-quality fiber-rich feed, produces the potent greenhouse gas methane (CH4) as a by-product. It has been proposed that saponin-rich plants can be used to reduce CH4 emissions from ruminant livestock, although the reported results are variable in terms of efficacy. Here we use meta-analytical methods to investigate the literature to determine if saponins can contribute to reducing CH4 production and its further effects on other rumen fermentation parameters in sheep. Following defined search terms available papers on the subject were collected for the period 1990 to 2019 and inclusion and exclusion criteria were applied, an analysis was conducted on CH4 production, CH4 per dry matter intake (DMI), ruminal pH, total volatile fatty acid (VFA), acetate, propionate, butyrate, and acetate-to-propionate ratio based on a comparison between a saponin supplemented group and a control group.The standardized effect size (Hedges’ g) was calculated at the confidence interval of 95%. Q-test and I2 statistic were used to determine heterogeneity and publication bias was identified through the Egger test. The meta-analysis determined that using saponin sources tended to decrease CH4 production (P=0.062) and acetate-to-propionate ratio (P=0.057), with a reduction in CH4/DMI (P=0.001) and an increase in propionate concentration (P=0.011). No significant difference was observed in ruminal pH, total VFA concentration, and butyrate concentration. The I2 statistic for the parameters analyzed here was below 50% for heterogeneity with the Egger test results indicating a publication bias for CH4 production.