Genetic parameters for blood urea nitrogen, methane emissions, and feed intake in Hereford beef cattle

Abstract

The objective of this project was to estimate heritabilities and evaluate genetic and phenotypic correlations among three key environmental impact traits: dry matter intake (DMI), methane (CH4) emissions, and blood urea nitrogen (BUN)—a proxy for nitrogen metabolism—in a population of Hereford cattle. Enteric methane (CH4) emissions and nitrogen excretion from beef cattle are major contributors to agriculture's environmental footprint. DMI is a critical trait because it influences the amount of nutrients consumed and metabolized by the animal, thereby affecting both CH4 production and nitrogen excretion. Data were collected from 728 animals across six trials from 2021 to 2024, with phenotypes obtained using the Vytelle intake system (Vytelle, Greeley, CO), GreenFeed head-chamber system (C-Lock Inc., Rapid City, SD), and colorimetric BUN assays (Thermo Fisher Scientific, Waltham, MA). A three-trait animal model was fitted using ASReml 3.0 to estimate genetic parameters. Fixed effects in the model included trait-specific contemporary groups (CG; DMI, CH4, BUN) and animal age at the time of measurement to account for environmental and developmental variation. Heritability estimates were moderate for BUN (0.19 ± 0.16) and CH4 (0.28 ± 0.25), and high for DMI (0.53 ± 0.14), indicating meaningful potential for genetic improvement. A strong genetic correlation was observed between BUN and DMI (0.82 ± 0.37), suggesting overlapping genetic control of nitrogen metabolism and feed intake, while genetic correlations between CH₄ and the other traits were weak or negative. Residual correlations revealed environmental drivers strongly influencing CH4 and DMI (0.89 ± 0.29) and a potential trade-off between BUN and DMI (-0.29 ± 0.21). These results support the feasibility of genetic selection for reduced environmental impact through reduced CH4 emissions and improved nitrogen efficiency. Further validation in larger, multi-breed populations is warranted. Incorporating traits like BUN and CH4 into breeding programs may enable long-term reductions in livestock-related environmental impacts without compromising productivity.