Abstract Exploring how residual methane production (RMP) relates to productivity may reveal opportunities for selecting animals with lower methane emissions without impacting performance. This trial aimed to evaluate differences in average daily gain (ADG), dry matter intake (DMI), feed efficiency, body composition and gaseous exchange in growing beef heifers with divergent phenotypes for RMP. Growing beef heifers (n = 97; initial BW = 264 ± 25 kg) with high genetic variability were assigned randomly to one of two blocks. Both blocks were evaluated during an 84-day feed efficiency test using individual feed bunks (American Calan Inc.), during which time individual DMI and BW were recorded to determine ADG and feed efficiency. Carcass ultrasound data were collected at the end of the study. Each animal also participated in an energy metabolism study, that included four consecutive days of total fecal and urine collections and one day of methane (CH4), carbon dioxide (CO2), and oxygen (O2) exchange measurements using headboxes (HB) through an indirect calorimetry method. All heifers were fed a common diet of 80% corn silage, 15% dried distillers grains, and 5% supplement (DM basis), offered ad libitum. Residual methane production was calculated within block from the regression of CH4 on metabolic body weight (MBW) and DMI measured while heifers were in the HB. Heifers were divided into one of three RMP classes (± 0.5 SD from the mean block RMP). Data were analyzed using a mixed model including RMP classification and block as fixed effects. Low RMP heifers emitted 27.8% less CH4 (g/d; P 0.001) and 32.3% less CH4 yield (g/kg DMI; P 0.001). Similarly, compared to high RMP heifers, low RMP heifers produced 10.4% less CO2 (g/d; P = 0.033) and consumed 11.6% less O2 (g/d; P = 0.011). During the feed efficiency test, there were no differences in initial and ending BW, ADG, DMI, gain-to-feed ratio, longissimus muscle area or intramuscular fat (P 0.399) between heifers with high and low RMP phenotypes. In terms of metabolism traits, there were no differences for MBW, DMI, or dry matter digestibility (P 0.691) between heifers with divergent RMP phenotypes. Using Pearson’s correlations, DMI during the feed efficiency test was positively associated with ADG (r = 0.55; P 0.001) and DMI measured in the headbox was positively associated with CH4 production (r = 0.66; P 0.001), highlighting the role of feed intake in growth and CH4 emissions. Gain (r = 0.16; P = 0.128) and feed efficiency (r = -0.04; P = 0.674) were not associated with RMP; however, low RMP heifers emitted 27.8% less methane (g/d). These results suggest that selecting for reduced RMP could lower methane emissions without impacting productivity.
Simeone et al. (Wed,) studied this question.