Influence of ruminal methane on digesta retention and digestive physiology in non-lactating dairy cattle

Enteric methane (CH4) production is a side-effect of herbivore digestion, but it is unknown whether CH4 itself influences digestive physiology. We investigated the effect of adding CH4 to, or reducing it in, the reticulorumen (RR) in a 4x4 Latin square experiment with rumen-fistulated, non-lactating cows, with four treatments: (i) control, (ii) insufflation of CH4 (iCH(4)), (iii) N via rumen fistula, (iv) reduction of CH4 via administration of bromochloromethane (BCM). DM intake (DMI), apparent total tract digestibility, digesta mean retention times (MRT), rumen motility and chewing activity, spot breath CH4 emission (CH(4)exhal, litre/kg DMI) as well as CH4 dissolved in rumen fluid (CH(4)RRf, mu g/ml) were measured. Data were analysed using mixed models, including treatment (or, alternatively, CH(4)exhal or CH(4)RRf) and DMI relative to body mass(085) (rDMI) as covariates. rDMI was the lowest on the BCM treatment. CH(4)exhal was highest for iCH(4) and lowest for BCM treatments, whereas only BCM affected (reduced) CH(4)RRf. After adjusting for rDMI, CH(4)RRf had a negative association with MRT in the gastrointestinal tract but not in the RR, and negative associations with fibre digestibility and measures of rumination activity. Adjusting for rDMI, CH(4)exhal had additionally a negative association with particle MRT in the RR and a positive association with rumen motility. Thus, higher rumen levels of CH4 (CH(4)exhal or CH(4)RRf) were associated with shorter MRT and increased motility. These findings are tentatively interpreted as a feedback mechanism in the ruminant digestive tract that aims at mitigating CH4 losses by shortening MRT at higher CH4.