173 Awardee Talk: Spot Sample Protocol for Gas Quantification of Grazing Beef Cattle Using a Greenfeed

Abstract

Abstract Through a natural digestive process called enteric fermentation, cattle produce greenhouse gases that are an environmental concern and an energetic loss. Gas fluxes can be quantified with several techniques; however, an open circuit gas quantification system (OCGQS) allows for unencumbered quantification of methane (CH4), carbon dioxide (CO2), and oxygen (O2) from grazing cattle. In the literature, there is wide variation in the minimum number of spot samples recommended to evaluate gas fluxes of an individual animal, while no recommendations have been made to evaluate metabolic heat production. The objective of this study was to characterize the minimum number of spot samples needed to accurately quantify metabolic heat production and CH4, CO2, and O2 gas fluxes in grazing beef cattle. A minimum of 100 spot samples each were collected from seventeen grazing animals using a OCGQS (GreenFeed, C-Lock, Inc). The mean gas fluxes were computed starting from the first 10 visits (forward) and increasing by increments of 10 until 100 visits was reached. Mean gas fluxes were also computed starting from visit 100 moving back in time in increments of 10 (reverse) using the same approach. Mean gas fluxes were used to calculate individual animal metabolic heat production for each interval with both the forward and reverse approaches. Pearson and Spearman correlations were computed between the full 100 visits and each shortened visit interval. The minimum number of spot samples was determined when correlations with the full 100 visits were greater than 0.95. The 0.95 correlation threshold was met between 30 and 40 visits for all gas fluxes and metabolic heat production. Therefore, mean forward and reverse gas fluxes and metabolic heat production were also computed starting at 30 visits and increasing by 2 until 40 visits and vice versa. The results indicated that the minimum number of spot samples needed for accurate quantification of CH4, CO2, and O2 gas fluxes are 38, 40, and 40, respectively. Using gas fluxes collected by the OCGQS, metabolic heat production can be calculated after 36 spot samples. The practical calculation of metabolic heat production will require 40 spot samples given the necessary number of spot samples for component gases in the calculation. Animals met the required number of spot samples for quantification of metabolic heat production, CH4, CO2, and O2 in 29.5 ± 8.7, 30.5 ± 9.1, 31.8 ± 9.2, and 31.8 ± 9.2 days, respectively. Large variation existed around the number of days needed to achieve the recommended number of spot samples. For this reason, protocols for the OCGQS should be based on the total number of spot samples, rather than a test duration.