PS9-26. Estimates of Genetic Parameters for Enteric Gas Fluxes in US Beef Cattle.

Abstract Enteric methane (CH4) is a major source of greenhouse gas emissions in beef production systems and represents an energetic loss diminishing production efficiency. As such, CH4 and carbon dioxide (CO2) emissions, together with oxygen (O2) consumption, have been evaluated as indicators of feed intake and efficiency. Genetic selection to improve feed efficiency offers a powerful approach to mitigating CH4 emissions, given the cumulative and permanent nature of genetic gains. This study aimed to assess genetic variability and estimate the heritability of enteric gas fluxes in beef cattle. Data were collected in one commercial farm (Nichols Farms, Bridgewater, IA) from 879 animals (362 Angus, 175 Simmental, 48 South Devon, and 294 crossbreeds), with a total of 1,753 individuals represented in the pedigree relationship matrix. Daily averages (g/d) of CH4 and CO2 emissions, and O2 consumptions were measured by GreenFeed (C-Lock Inc., Rapid City, SD) as animals rotated through two pens every 8 to 21 days during the 60-d performance test. Daily averages (g/d) of CH4, CO2, and O2 were 177.8 ± 36.3, 7451.8 ± 1130.4, and 5129.1 ± 1465.0, respectively. Genetic parameters were estimated under an animal model implemented using the BLUPF90 package. Fixed effects included breed group and RFI contemporary group (year born, sex, and feed efficiency test group), with animal age fitted as linear and quadratic covariates. The additive genetic effect of the animal was included as a random effect using the pedigree-based relationship matrix. Variance components were estimated using restricted maximum likelihood (REML). Phenotypic variances of CH4, CO2, and O2 were 965.6, 580.5, and 291, respectively. Additive genetic variances of CH4, CO2, and O2 were 396.5 ± 125.0, 183.9 ± 72.4, and 136.0 ± 42.2, correspondingly. The heritability estimates of CH4, CO2, and O2 were 0.41 ± 0.13, 0.32 ± 0.12, and 0.47 ± 0.15, following this order. Our findings indicate that enteric gas fluxes are heritable traits in beef cattle, with a substantial proportion of phenotypic variance explained by additive genetic effects. The moderate to high heritability estimates obtained in this study suggest that CH4, CO2, and O2 have the potential to be incorporated into genetic improvement programs. Selection for these traits could contribute to reducing methane emissions or improving efficiency, supporting the development of more sustainable beef production systems.