Technical Note: Effect of bait delivery interval in an automated head-chamber system on respiration gas estimates when cattle are grazing rangeland

ABSTRACT Agricultural methane (CH 4 ) emissions worldwide account for approximately 43% of all anthropogenic CH 4 emissions, and the majority of agricultural CH 4 emissions are attributed to enteric fermentation within ruminant livestock. Therefore, interest is heightened in quantifying and mitigating this source. The automated head-chamber system (AHCS; GreenFeed, C-Lock Inc., Rapid City, SD) evaluated here can be placed in a pasture with grazing cattle to measure their CH 4 and CO 2 emissions and O 2 consumption. However, improper management of an AHCS might have a significant effect on gas exchange estimates. One factor that may affect the quality of these estimates is the rate that bait is delivered and the length of time an animal has its muzzle in front of the intake manifold for sampling. During both experiments, at each visit to the AHCS an electronic ear tag triggered the delivery of 6-mm alfalfa pellets (bait; 32-g increments) at timed intervals up to 8 times per visit and a maximum of 4 sampling events/d. In Exp. 1, the AHCS was programmed to deliver feed at 18- (n = 2), 21- (n = 4), 24- (n = 4), or 27-s (n = 3) intervals for 73 d; in Exp. 2 the AHCS was programmed to deliver feed at 19- (n = 2), 27- (n = 4), 35- (n = 4), or 43-s (n = 3) intervals for 43 d. The AHCS was programmed to measure CH 4 , CO 2 , and O 2 (Exp. 2 only) fluxes at each visit during the experiments. Time intervals were analyzed by ANOVA, and least squares means were compared using linear and quadratic contrasts. Carbon dioxide emission estimates were not affected by time interval in either experiment. Methane emission estimates and the ratio of CH 4 :CO 2 linearly decreased ( P 2 consumption estimate in Exp. 2. Increasing the time increment increased ( P