The use of plant by-products as non-conventional feedstuff for livestock feeding with reference to rumen methanogenesis

Global warming has turned as a global concern for especially those who engaged in animal agriculture. The use of non-conventional feedstuff (e.g., plants and plant extracts) has also become an interesting topic since they are natural products, environmentally friendly and safe in food production. These potential feed additives are rich sources of secondary compounds. The ideal effects of these plant secondary compounds on ruminant would be to reduce methane (CH 4 ) production with no negative effect on rumen fermentation characteristics. The aim of the present review was to summarize the related studies from published papers in recent years. Based on published data, plants and plant extracts of various origins have shown to inhibit ruminal CH 4 production (methanogenesis) when fed to ruminants either as forages or as extracts tested in vitro or in vivo. The suppressed methanogenesis was mostly attributed to improving fermentation characteristics (e.g., increase in propionic concentration) as well as antimethanogenic and antiprotozoal activities of these feedstuff. However, it should be noted that the effectiveness of these feed additives depends on the source, type and level at which they are being used. In conclusion, plants and plant extracts seem promising as feed supplements for ruminant nutrition.