Genetic insights into enteric methane emissions in indoor-fed growing cattle

Despite increasing interest in the genetic selection of ruminants for reduced enteric methane emissions, uncertainty remains on which methane trait definitions best reflect the exploitable genetic variation independent of traits already included in national cattle breeding programs. The present study aimed to explore the genetic variability in a range of methane-related traits in growing beef cattle and quantify the proportion of genetic variance in daily methane production that is independent of performance traits such as feed intake, growth, and body size. Methane and carbon dioxide emissions were measured using GreenFeed systems on 1,700 growing crossbred beef cattle from a commercial feedlot. Performance traits, including energy intake, feeding behavior, liveweight, live animal ultrasound, subjective skeletal and muscular scores, and slaughter data were also available. Thirteen methane traits were generated, comprising daily methane production, five ratio traits, and seven residual methane production (RMP) traits, each statistically adjusted for different combinations of energy intake, liveweight, average daily gain (ADG), and carcass weight. Genetic parameters were estimated using animal linear mixed models. Daily methane production was moderately heritable (0.42 ± 0.09), with a genetic standard deviation of 23.43 g/d. Daily methane production exhibited moderate genetic correlations with feed intake (0.51), ADG (0.39), metabolic liveweight (0.27), and carcass weight (0.42). These correlations suggest commonalities in the genetic architecture between methane production and traits related to feed intake, body size, and growth rate. Genetic adjustment of daily methane production for these traits resulted in a 25% reduction in the genetic standard deviation (from 23.43 g/d to 17.55 g/d), with only 56% of daily methane productions genetic variance remaining independent of the performance traits. Heritability estimates for the RMP traits ranged from 0.38 ± 0.09 to 0.46 ± 0.09, and their genetic correlations with daily methane production remained strongly positive (>0.84). These results suggest that while genetic selection can reduce methane emissions in growing beef cattle, a substantial portion of the genetic variation in daily enteric methane emissions overlaps with traits already under selection. Thus, consideration needs to be given to the genetic correlations between methane emissions and other traits already under selection when attempting to quantify the cost benefit of genetically selecting on methane emissions.