Examining the inter- and intraspecies variability in the polyphenolic profile and in vitro antimethanogenic potential of forage species
Methane (CH4) emissions from ruminants represent around 39% of the global agricultural greenhouse gas emissions. Inclusion of tannin-rich forages (TRFs) in animal diet has emerged to be one of the most promising strategies to reduce CH4 emissions in ruminants as they can also potentially improve animal health and productivity by increasing live weight gains, wool production, and increase milk and meat production. However, the results from the studies on TRFs till date, have so far been highly inconsistent and their utilisation on field scale has been difficult. To overcome these variabilities, we conducted a greenhouse experiment with 17 cultivars from 8 different forage species. The plants were grown under identical environmental conditions and were harvested thrice at the same phenological stage. The leaf samples from the plants were examined for their polyphenolic composition and proanthocyanidin (PA) structural traits. The interspecies variability across the species, for both PA concentration and structural traits, was found to be higher than variation within the cultivars of the same species as well as variation across the harvests. To assess whether the observed variability in polyphenols and tannins affects the bioactivity of these forages, hohenheim gas test was conducted to determine CH4 reduction potential of these species, using lucerne as a tannin-free negative control. With the exception of birdsfoot trefoil cultivars, all the tested species reduced CH4 production by up to 48% compared to lucerne. However, tannins in the forages were found to negatively affect the digestibility of the feed. Plantain and chicory were the most promising candidates from our experiment, as despite their comparatively lower CH4 reduction potential, they had no negative effect on the digestibility of the feed.