Unraveling factors influencing the variability and repeatability of greenhouse gases measured through an automated head chamber system in grazing cattle in commercial conditions.

Global concern about the environmental impact of livestock production has been increasing over the past decade; consequently, research has focused on mitigating these emissions. Among all devices deployed to access greenhouse gases (GHG), the GreenFeed (GF) system is the most used for grazing systems. Nonetheless, the primary issue about GF use is its higher variability and the low repeatability (R) of GHG measurements in grazing individuals compared to other methods. Thus, this work aimed to assess both environmental and animal factors, as well as the variability of the GF itself, to explain GHG variability in cattle. These evaluations are usually conducted under experimental conditions, but in this work, both the variability and R values of CH4 were analyzed under commercial settings. Three and two GF units were deployed simultaneously in a dry lot and then in a grazing pasture, respectively, on a commercial cattle ranch. To evaluate the variability and R values of GHG, the GF collected enteric emissions, wind speed, wind direction, temperature, and animal data from 175 and 169 Angus heifers in dry lot and pasture settings, respectively. Variance component analyses were used to evaluate the influence of these factors on the GHG measurements. Results showed a coefficient of variation (CV) of CH4 and CO2 measured through the GF of 32% and 20%, respectively. Of the total CH4 variation in grazing conditions, 2.73% was explained by environmental factors and 38.3% was explained by animal factors, including feeding behavior (4.58%), between-animal variation (16.4%), date of the visit (12.5%), hour of the visits (3.05%), visits' duration (1.78%), and number of visits/day (1.25%). In contrast, in the dry lot, environmental and animal factors explained 7.49% and 8.58% of the CH4 variation, respectively. Finally, the GF equipment itself explained 0.15% and 2.06% of the variation of the CH4 in the grazing and dry lot conditions, respectively. The R values, measured as the animal variance divided by the sum of animal and error variances, increased linearly (0.094 to 0.23) in the dry lot, while in the grazing settings, it decreased linearly (0.098 to 0.056) from days 1 to 21. This study identified the most influential factors contributing to the variability of GHG emissions and the low R values of CH4 in commercial grazing cattle production, paving the way for enhanced future use of GF devices for reporting GHG emissions in grazing systems.