Repeatability of carbon dioxide and methane emissions and oxygen consumption by forage-consuming beef heifers

Authors: MACNEIL, MICHAEL - University Of The Free State; Waterman, Richard

Submitted to: Animal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2025
Publication Date: 2/20/2025
Citation: MacNeil, M., Waterman, R.C. 2025. Repeatability of carbon dioxide and methane emissions and oxygen consumption by forage-consuming beef heifers. Animal. 19(4). Article 101469. https://doi.org/10.1016/j.animal.2025.101469.
DOI: https://doi.org/10.1016/j.animal.2025.101469

Interpretive Summary: Research that investigates the contribution of respiratory gases to global warming must be fundamentally and statistically accurate to allow mitigation procedures to be derived and implemented by livestock managers. Violations of sound experimental procedures will lead to false conclusions and provide industry recommendations that will compromise creditability of the science and ultimately impact beef production in a negative manner. In this pilot study 30 heifers were continually monitored for 414 days and daily respiration measurements of methane (CH4), Carbon dioxide (CO2) and oxygen (O2) were monitored using a automated head-chamber system (ACHS; Greenfeed: C-Lock, Inc., Rapid City, SD). In this pilot study, statistical power of the test was evaluated for experiments comparing two treatments and for the comparison of an observed mean against a threshold. For an individual animal, methane required 45 days of measurements to obtain a mean with 80% accuracy. Carbon dioxide required data from fewer days (28). Given the cost of the technology to measure gases in the grazing situation and its limited capacity, some care will be required in designing appropriate experiments and to properly interpret the observed effects particularly when they are not statistically significant.

Technical Abstract: Gas exchange by ruminant livestock is deemed as a contributor to climate change. As such research to reduce the production of greenhouse gasses is an emerging need. It is important that these studies reach definitive outcomes. Because the majority of cows are sustained by grazing forages, the objective of this study was to assess the variation in CH4 and CO2 emissions and O2 consumption among forage-consuming beef cattle. Recommendations as to the number of days over which data needs to be collected and numbers of experimental units that need to be used in comparing treatments can be inferred from this information. Heifers (n=30) from a three-breed composite population of beef cattle were used in this research. They were introduced to a portable automated head-chamber system in January 2023 and had continuous access to the system through February 2024 (414 d). Data were uploaded to a server and proprietary algorithms were used to calculate CH4 and CO2 emission and O2 consumption of the heifers. Repeatability of the daily average values were calculated, and estimates were used to infer the accuracy of measurements obtained over varying numbers of days. The numbers of heifers that are required to achieve a specified power-of-the-test for an experiment comparing two treatments and for the comparison of an observed mean against a threshold were calculated. Methane required 45 days of measurements to obtain a mean with 80% accuracy. Carbon dioxide required data from fewer days (28). Given the cost of the technology to measure gases in the grazing situation and its limited capacity, some care will be required in designing appropriate experiments and to properly interpret the observed effects particularly when they are not statistically significant.