Understanding variability and repeatability of enteric methane production in feedlot cattle
K. A. Beauchemin, Paul Tamayao, Christine Rosser, Stephanie A. Terry, Robert Gruninger
Abstract
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 <12 visits and <5 blocks were omitted for the period and animals with ≥2 periods of complete CH 4 data were used in the final analysis (n=52). Animals were ranked based on CH 4 yield (g/kg DMI) from low to high, and grouped as Very-low (≤10% of animals), Low (11-25%), Intermediate (26-74%), High (75-89%), and Very high (≥90%) emitters (mean ± SD, 12.6 ± 2.16). The CH 4 yield was 16% less ( P <0.05) for Very-low compared with Intermediate animals due to lower CH 4 production (g/d, P <0.05), with no differences in DMI ( P >0.05). However, the period × grouping interaction ( P <0.001) for CH 4 yield indicated that the ranking of animals changed over time, although there were no extreme changes in rankings. Total VFA concentration decreased as CH 4 yield decreased, but molar proportions of VFA remained unchanged, suggesting lower extent of ruminal digestion rather than a shift in fermentation. There were no differences in feeding behavior or average daily gain among groupings ( P >0.05). The between-animal coefficient of variation in CH 4 yield of 17.3% enabled identification of low CH 4 -emmitting finishing beef cattle. However, accurate selection of low CH 4 -emitting animals should be based on repeated CH 4 measurements over the production cycle.