In vitro study of halloysite-kaolinite mixed mineral added to cattle rumen fluid: methane abatement and the fate of ruminal biota

Abstract Cattle are primary livestock, but they burp methane, a potent greenhouse gas. This is caused by microbial fermentation in the rumen, a process known as methanogenesis. Ruminal archaea, bacteria, protozoa, fungi, and nematodes take part directly and indirectly in this process. Feed supplements have become a feasible way of inhibiting methanogenesis. Considering that cattle are naturally geophagic, clay minerals, particularly kaolin, are being added to those supplements with the expectation that they will reduce enteric methane. The present study characterized a halloysite-kaolinite mixed mineral sample collected from a prospective deposit in Western Australia. The clay was mixed into grass mash to formulate a cattle diet. An in vitro experiment was conducted using the ANKOM system and viable rumen fluid to simulate cattle rumen fermentation. Rumen parameters, such as dissolved oxygen, oxidation-reduction potential, pH, and volatile fatty acids, were measured. Methane was produced as a result of rumen function, and its kinetic concentrations were measured. Scanning electron microscopy (SEM) of the rumen sample revealed clusters of kaolin-associated nematodes. Microbial diversity and functional community analyses were performed using 16S rRNA sequencing. Post-fermentation changes in kaolin minerals were assessed using SEM and X-ray diffractometry (XRD). The inclusion of kaolin significantly reduced methane production by 22.5% ( p < 0.05). This intervention did not affect the other fermentation parameters, microbial population, or clay composition. However, kaolin might reduce the mobility and survival of nematodes through physical attachment. Overall, these results indicate that raw halloysite-kaolinite mixed mineral can reduce enteric methane production without disrupting the measured ruminal fermentation parameters or the structural stability of the clay mineral. This study provides valuable insights into the inclusion of halloysite-kaolinite mixed mineral in specialized cattle feed additives.