Methane

Methane (CH₄) production from enteric fermentation of ruminant animals, such as beef cattle, impacts all three pillars of sustainability- environment, economic, and social. Several collection methods can quantify CH₄ emissions from beef cattle. Respiration chambers, the GreenFeed (C-Lock Inc.), the sulfur-hexafluoride tracer technique, infrared spectroscopy, and sniffers are currently the most common collection methods. Each collection method has distinct advantages and disadvantages for application to large scale genetic evaluations. The most high-throughput methods to collect CH₄ phenotypes are the GreenFeed and sniffers. However, there are barriers to the implementation of these technologies. The GreenFeed is labor-intensive and costly. Whereas, sniffers, which are less expensive and require less labor, may be more suitable for ranking animals rather than providing absolute measurements as CH₄ concentration (ppm) is reported rather than CH₄ production (g/d). As phenotyping CH₄ production for genetic evaluations continues, development of more standardized phenotyping protocols for the GreenFeed and sniffers should be considered.

Although feed additives and dietary modifications have proven effective in reducing CH₄ emissions, their mitigation effects persist only with continuous use. Other concerns include rumen adaptation to the treatment and practical application in grazing systems. In contrast, genetic selection for reduced CH₄ emissions would result in permanent and cumulative changes.

Phenotype

Daily methane production (grams/day) is the most direct phenotype to characterize CH₄ production. Other phenotypes can be calculated from daily methane production and related component traits, such as methane yield (g CH₄/kg dry matter intake (DMI)) and methane intensity (g CH₄/unit of animal product), similar to what is seen for DMI. These calculated traits are ratio traits that require additional animal information to calculate which may not be available in some production situations (i.e. feed intake while grazing).

Residual methane production (RMP) also has been proposed, which is calculated similarly to residual feed intake (RFI) or residual average daily gain. Although multiple calculations of RMP have been published, it is generally defined as the difference between observed and expected methane production calculated by the regression of methane production on DMI (and possibly other variables). Observed CH₄ production is adjusted for phenotypically correlated sources of variation, so that RMP is not correlated with those traits. Similar to BIF’s recommendations for selection on DMI rather than RFI, selection for reduced CH₄ production should involve the direct trait rather than a RMP trait. Moreover, development of an economic selection index would be beneficial to select for reduced CH₄ production with other appropriate economically relevant traits considered.

Identification of indicator traits that are correlated with CH4 production, but easier and/or less expensive to measure is a possible alternative. Indicator traits may be less effective for selection but would allow for a larger number of animals to be phenotyped.

Adjusted Value

No adjustments factors have been developed for methane phenotypes.

Contemporary Group

Contemporary groups for CH₄ production phenotyping should be similar in age, sex, and breed composition and receive similar management. All cattle within a contemporary group should have CH₄ production measured using the same collection method and protocol. Diet composition is known to influence CH₄ production. Therefore, diet should also be consistent within contemporary groups.

It is still unclear at which stage of production (grazing or confinement) animals should be phenotyped. Updates to these guidelines will be made in the future as research in this area develops.

Genetic Evaluation

Collection of CH₄ production data on a large scale, as required for genetic evaluation, has proven both difficult and expensive. Literature reports that CH₄ production (g/d) from cattle is a moderately heritable trait ranging from 0.21 ± 0.06 to 0.30 ± 0.06 suggesting genetic selection is possible. Successful implementation of a genetic evaluation for methane traits will likely require collaboration across the beef industry.

Recommendations

BIF recommends that selection for reduced enteric CH₄ production should not be based on a RMP trait. Incorporation of an enteric CH₄ production trait into an economic selection index would be the most practical usage of this trait.

Attribution

This article is a derivative of work performed by Elizabeth Dressler and Dr. Megan Rolf.