Influence of sampling time on carbon dioxide and methane emissions by grazing cattle

Authors: Gunter, Stacey; Bradford, James

Submitted to: American Society of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/9/2015
Publication Date: 6/23/2015
Citation: Gunter, S.A., Bradford, J.A. 2015. Influence of sampling time on carbon dioxide and methane emissions by grazing cattle. American Society of Animal Science Proceedings. 66:201-203.

Interpretive Summary: A need to respond to global climate change has focused great attention towards greenhouse gases (carbon dioxide and methane) produced by domestic ruminants and mitigation of their greenhouse gas emission. Respiration chambers have long been the preferred method to measure greenhouse gas emission by cattle. With quickly advancing technology, automated head chambers are now available as a research tool that measures the greenhouse gas emission by grazing cattle in their natural environment. With these new systems, cattle are enticed to place their head in the chamber with feed and while they consume this bait, the chamber collects a breath sample and analyzes it for greenhouse gases. A criticism of this system is that it only measures greenhouse gas while the animal is feeding, possibly only 3 to 12 minute per day. Data collected over a 64-day period was separated into early morning (midnight to 5:59 am), late morning (6:00 am to 11:59 am), afternoon (noon to 15:59 pm), and evening (6:00 pm to 11:59 pm) periods. When breath samples were collected in the late morning they tended to predict lower carbon dioxide emission by cattle, but methane emissions predictions were definitely lower in the late morning. But, because differences were small among the daily periods, as long as research ensures that breath sampling occurs across the entire day they can be confident ‘spot sampling’ will provide quality and accurate predictions of greenhouse gas emission by cattle.

Technical Abstract: A need to respond to global climate change has focused great attention towards greenhouse gases produced by domestic ruminants and gas emission mitigation. Respiration chambers have long been the preferred method to measure CO2 and CH4 emission by cattle. With quickly advancing technology, automated head chambers are now available as a research tool that measures the CO2 and CH4 emission by cattle. With this system, cattle are enticed to place their head in the chamber with feed and while they consume this bait, the chamber collects a breath sample and analyzes CO2 and CH4. A criticism of this system is that it only measures CO2 and CH4 while the animal is feeding, possibly only 3 to 12 min/d. Data collected over a 64-d collection period (n = 2,377) was separated into early morning (0000 to 0559), late morning (0600 to 1159), afternoon (1200 to 1759), and evening (1800 to 2359) samples. Carbon dioxide emission tended (P = 0.10) to be less when samples were collected in the late morning, but differences were small. Further, CH4 emissions did differ (P = 0.07) among periods, with later morning sampling producing the least CH4 emission (199 g/d) and evening sampling producing the greatest CH4 emission (235 g/d). In a further analysis, 3 data sets were produced with sampling occurring over the entire day (ALL), only in the MORNING (0500 to 1059), and only in the EVENING (1400 to 1959) which could occur in some research situations. Methane (P = 0.98) and CO2 (P = 0.35) emission estimates did not differ among sampling scenarios. As a result of this analysis, researchers can be confident in ‘spot sampling’ when assurances are made to collect representative samples in sufficient numbers.