59 Feeding behavior in divergent residual enteric methane emissions steers during the backgrounding and finishing phases

Abstract Enteric methane (CH4) is produced during the anaerobic fermentation of organic matter and represents an energy loss for ruminants. Diet and animal characteristics mainly determine CH4 emissions. However, there is limited information regarding the relationship between feeding behavior and CH4 emissions in growing steers consuming different diets. This experiment aimed to evaluate the feeding behavior of growing steers with divergent residual methane emissions (RCH4) during the backgrounding and finishing phases. Two hypotheses were evaluated: 1) the steers would not change the initial RCH4 classification when moving from backgrounding to finishing phases, and 2) steers with divergent RCH4 would show different feeding behavior. Angus steers (n = 60) were placed in two pens and were classified as high, medium, and low RCH4 during both phases. During the backgrounding phase, steers 209 ± 26 kg of initial body weight (BW) were fed a total mixed ratio (TMR) with 46% neutral detergent fiber (NDF) and 0.86 Mcal/kg DM of net energy of gain (NEg) for 60 d. During the finishing phase, steers (517 ± 40 kg of initial BW) were fed a TMR with 16.8% NDF and 1.37 Mcal/kg DM of NEg for 80 d. Feed intake and gas flux were determined daily using Smartfeed and Greenfeed technology. Steers were weighed every 2 wk during each phase to determine average daily gain (ADG). The number of meals (NM), meal size (MS), time per meal (TM), intervals between meals (IM), and intake rate (IR) were calculated using 5 min as a meal criterion. Individual RCH4 classification rank during the backgrounding and finishing phases was analyzed using a chi-square test. Feeding behavior was analyzed using a mixed model with RCH4 classification and animal as fixed and random effects, respectively. No relation (P = 0.5) existed between individual RCH4 classification during the backgrounding and the subsequent RCH4 classification during the finishing phase. In either phase, feed intake or ADG was not different (P 0.05) among divergent RCH4 groups. Feeding behavior was not different (P 0.05) among RCH4 groups during the backgrounding phase, but MS and TM were greater (P 0.05) in steers with high RCH4 during the finishing phase. Steers classified as low RCH4 showed less CO2 and CH4 production and less O2 consumption than medium and high RCH4 in either phase. In conclusion, growing steers were re-ranked according to the RCH4 classification during the backgrounding and finishing phases. Animal performance was not related to RCH4 classification. However, steers with decreased RCH4 showed less MS during the finishing phase. Also, CO2 and CH4 were less in low RCH4 steers during both phases. Further work should be conducted to recognize differences in fermentation and metabolism of lower RCH4 steers for developing selection and management interventions.