Simulating the number of spot-samples required to estimate the methane to carbon dioxide ratio in lambs and its relationship with methane yield

ABSTRACT

Measuring the methane to carbon dioxide ratio (CH₄/CO₂) from animals could be useful to predict CH₄ yield when dry matter intake (DMI) cannot be measured. The objectives were to (1) evaluate the relationship of CH₄/CO₂ with CH₄ yield; (2) compare the CH₄/CO₂ of 10–60 simulated spot-samples with the CH₄/CO₂ calculated with data from 48-h of respiration chamber measurements. The DMI and CH₄ and CO₂ emissions measured every 5–6 min in respiration chambers from a previous experiment with 70 lambs fed ryegrass substituted with 0%, 25%, 50%, 75% and 100% of forage rape were retrieved. Emission data were used to perform simulations of 10, 20, 30, 40, 50 and 60 randomly selected spot-samples per lamb. The CH₄/CO₂ of 20 or more spot-samples was useful to predict CH₄ yield and detect differences between dietary treatments, while the precision of the prediction increased when increasing the number of spot-samples up to 50 samples per lamb. Twenty spot-samples were sufficient to obtain accurate CH₄/CO₂ estimates; however, variance decreased (precision improved) with an increasing number of spot-samples per lamb up to 50 spot-samples. The CH₄/CO₂ of 10–60 simulated spot-samples explained 61% to 66% of variation in the 48-h measured CH₄ yield.

KEYWORDS:

• Greenhouse gases
• fresh forages
• sheep
• predictors
• spot-samples

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by New Zealand Agricultural Greenhouse Gas Research Centre, and Maria Della Rosa was financially supported by the New Zealand Government through the Global Research Alliance Livestock Emissions & Abatement Research Network (LEARN) awards programme.