Analysis and review of publicly available GreenFeed results

Abstract Text:

The GreenFeed is a novel tool for measurement of enteric methane (CH₄) from ruminant animals.  The GreenFeed method uses repeated short-term measurement of CH₄ emitted from the animal in a feed trough while animals are receiving a feed reward.  To date, over 50 papers, conference proceeding, and reports are available that have used GreenFeed. The research covers a wide range of applications including method comparisons, animal genetics and dietary studies, and on-farm use.  In many studies, variability and repeatability of the GreenFeed data is reported.  The objective of this study was to aggregate the public data, analyze the results for overall accuracy compared to reference methods, summarize variability and repeatability of CH₄ emissions across applications, and to determine the strength of individual animal ranking relationships.  Overall, 22 method comparison trails ranging in herd averged emission from 150-485 g/d have been completed comparing GreenFeed to either the Sulfur Hexafluoride tracer method ( SF₆, 11 trials), respiration chambers (9 trials), or model predictions (2 trials).  The herd averaged results for the reference method compared to GreenFeed showed no significant slope bias (Reference = 0.99 x GreenFeed, R²=0.99) and the average absolute mean error for all trails was 6.4%.  For individual animal CH₄ emissions, GreenFeed measured CH₄ emissions were positively and moderately-to highly correlated with respiration chamber, SF₆, or modeled CH₄ in all but 4 trials.  In the 4 trials with less agreement for individual animals, the number of GreenFeed samples per animal was very low for some animals (4-10 samples) or there was no chamber replication.  GreenFeed measured CH₄ for individual animals also showed moderate correlations with DMI in three studies (r²=0.73, r² = 0.61, r=0.77), and in other studies was found to be higher (r²=0.42 and r²=0.47) than for SF₆ (r² = 0.17, r² = 0.08).  Between animal variation in GreenFeed CH₄ emissions were found to be the same, or lower than between animal variation in DMI, BW, or Respiration Chambers, or SF₆ in all but one trail.  Long term repeatability (R) of GreenFeed CH₄ emissions on forage based diets was R = 0.70 - 0.88 in 7 different trials.  Overall, the GreenFeed method produced similar absolute CH₄emissions estimates to reference methods, demonstrated the ability to rank animals, produced low but accurate between animal variability, and was highly repeatable on forage diets.

Keywords: GreenFeed, methane, emissions