Understanding variability and repeatability of enteric methane production in feedlot cattle

Breeding ruminants for low methane (CH 4 ) emissions can be permanent and cumulative, but requires a better understanding of the variability of CH 4 production among animals to accurately assess low-CH 4 phenotypes. Our objectives were to: 1) investigate the variation in CH 4 production among and within growing beef cattle, 2) identify low-CH 4 emitters, and 3) examine relationships between CH 4 production and intake, feeding behavior, growth, and rumen fermentation. Crossbred beef heifers (n=77; body weight=450 kg) were allocated to 3 pens and offered a finishing diet of 90% concentrate and 10% silage (dry matter (DM) basis). The study was conducted over 3 consecutive 6-week periods (126 days). GrowSafe bunks measured individual animal DM intake (DMI) and rumen fluid was sampled orally each period. A GreenFeed system measured individual animal emissions for 2 weeks/period. Methane production was calculated by animal within period using visits that were ≥3 min with fluxes compiled into six 4-h blocks corresponding to time of day, and averaged over blocks to obtain an average daily emission for the period. Animals with