Abstract Enteric methane production from beef cattle is a rising concern. The first step to lower emissions is the ability to obtain reliable measurements. Methane output was recorded using the GreenFeed system from C-lock; this system allows methane emissions to be measured daily at voluntary baited visits. The current GreenFeed testing length recommendation is 14-21 days for a free stall setting and 21 days for a pasture setting which includes a training period to acclimate animals. The objective of this study was to evaluate if data from a shorter test is as accurate as a prediction for methane emissions measured on the recommended 21 days. Measurements were collected from 160 heifers and bulls from a seedstock operation with an average age of 453.8 ± 22.5 days for heifers (n = 64) and 281.4 ± 61.8 days for bulls (n = 96). The data included 81 Angus, 16 South Devon, 20 Simmental, and 43 Angus Simmental cross. All animals evaluated had at least 21 days of valid testing days on a GreenFeed automated system. The average overall methane production was 179.7 ± 22.5 g/day and 165.9 ± 37.2 g/day for heifers and bulls, respectively. To evaluate the potential of shorter testing periods, individual animal emissions were averaged over 5, 10, 15, and 21-day periods. Linear regressions were performed to demonstrate the relationships between the shorter test period averages to the 21-day average for methane measurements. There was a strong positive relationship for all comparisons to the 21-day average with an improved prediction as the test length increased towards 21 days. Pearson correlation coefficients between 21-day measures to 5, 10, and 15-day periods were 0.86, 0.94, and 0.98, respectively. Estimated regression coefficients of methane emissions from a 21-day test on testing subsets were 0.73, 0.88, and 0.96 for 5, 10, and 15 days, respectively. Although the shorter test days were strongly associated with the 21-day average, they failed to reach unity and overestimated emissions from the 21-d test. Regression analysis comparing measurement windows of 5 to 21,10 to 21, and 15 to 21-day averages were compared to the mean of 21 days. The predictive power increased over time with estimated coefficients of 0.78 for 15 to 21 days, 0.92 for 10 to 21 days, and 0.98 for 5 to 21-day averages, indicating that longer days on test provides more stable estimates. Pearson correlation coefficients between the 21-day average to later test periods were 0.99, 0.96, and 0.89, indicating strong correlations with the 21-day average. In conclusion, these findings show that extended days on tests increased the accuracy of estimate of emissions when compared to 21-day tests, but shorter testing periods may not be a precise predictor for a 21-day test for methane emissions.
Condon et al. (Wed,) studied this question.