Can geophagy mitigate enteric methane emissions from cattle

Mitigation of ruminant methane (CH 4 ) production remains a formidable challenge for both improving feed conversion efficiency and decreasing emissions of this potent greenhouse gas but no viable solutions are yet available. We have taken a novel approach to addressing this challenge, based on our understanding of soil microbial ecology and clay mineralogy, and the practice of geophagy, that is, the deliberate consumption of soil materials including clay minerals by animals. In a series of preliminary in vitro studies, we have found that some clays can significantly, albeit inconsistently, reduce CH 4 production. A hydrothermally-derived kaolinite gave the most consistent results when the initial pH of the cow rumen content, used as an inoculum, was in the range of 6.0 to 6.2. In one in vitro incubation, this kaolinite (7.5 and 15 mg clay g -1 minced alfalfa), a condensed tannin (7.5 mg g -1 minced alfalfa), and a 1:1 kaolinite/condensed tannin mixture all caused a marked reduction in CH 4 production. Kaolinite has a lower surface area than the other clay minerals tested, so this finding suggests a common biological process that is related more to the pH-variable charge characteristics than the surface area of the clay sample. While the underlying mechanism is yet to be clarified, the use of suitable clays could potentially offer an animal- and environment-friendly approach to limiting enteric CH 4 emissions, especially when the rumen pH is depressed from feeding