Can Plant Saponins Lower Methane Emissions Without Hampering The Nutrient Digestibility of Ruminants?

Plant saponins have been used as additives to mitigate methane emissions originated from enteric fermentation of ruminant animals. Most of the studies however were based on in vitro techniques, and only limited studies were directly conducted on the animals. Inconsistencies of saponin effects on methane emissions have been previously observed, which might be related to their levels in rations. The present study was aimed to assess the effects of saponin levels on methane emissions and nutrient digestibility of ruminants in vivo by integrating data from multiple studies. A number of studies across 11 published articles were integrated into a database. Both small and large ruminant species were included. Searching of the articles was performed by using Scopus with keywords “saponin” and “methane”. The main criteria for a paper to be included were: (1) studies were conducted in vivo, (2) saponin contents were reported, and (3) methane was directly measured, not estimated by any methods. Parameters included in the database were methane emissions and nutrient digestibility. Data were analyzed by the statistical meta-analysis approach based on mixed model methodology. Different studies were treated as random effects while saponin levels in diets, i.e. control (no saponins), low (0 < saponins ≤ 5 g/kg) and high (saponins > 5 g/kg), were considered as fixed effects. Results revealed that, across all studies, methane emissions decreased significantly when saponins were added at both low and high levels (P<0.05), suggesting that the use of saponins for ruminants is beneficial in term of environmental conservation. Low levels of saponins increased nutrient digestibility as compared to control (P<0.05) while, on the contrary, high levels decreased the nutrient digestibility (P<0.05). It can be therefore concluded that the use of saponins at low levels is able to lower methane emissions of ruminants without hampering their digestibility.