Kaolin clay-based diets for managing livestock's health and methane emission problem

Increased livestock production is essential to meet the rising food and agri-services demand. However, livestock emit 70–95 % of agricultural methane (CH 4 ), a potent greenhouse gas, through their enteric fermentation. While various feed additives have been proposed to address CH 4 emissions and livestock production, this review highlights the potential of kaolin clays to serve these benefits by leveraging animals’ natural consumption habits. Over 136 non-human animal species are actively engaged in geophagy (earth-eating), and most of them prefer kaolin-rich soils. These animals routinely consume such soils as a source of essential minerals, and to manage gut parasites/pathogens, mycotoxins, gastrointestinal disorders, diarrhea, and acidosis. By learning from these feeding habits and their health benefits, raw and modified kaolin minerals can be used as feed ingredients in livestock’s regular diets. The unique morphology ( e.g. , platy kaolinite and hollow tubular halloysite) and surface properties ( e.g. , easy dispersion in solution to develop high Al 3+ and polyhydroxy-Al ions) of kaolin can reduce enteric CH 4 emissions by intervening in its related biochemical reactions, while enhancing animal production. At the same time, these added clay particles are excreted through the feces. Unprocessed kaolin may often contain iron as an impurity, which is typically considered an economic burden due to additional processing requirements. However, this kaolin can be beneficial as a feed ingredient as it can enhance enteric CH 4 inhibition as well as alleviate iron deficiencies in livestock. This review will also discuss possible modifications of kaolin prior to adding it as a feed supplement for better and more sustainable outcomes in managing CH 4 emissions, and animal health problems.