Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2017
Publication Date: 7/1/2017
Publication URL: https://handle.nal.usda.gov/10113/5801811
Citation: Gunter, S.A., Bradford, J.A. 2017. Technical Note: Effect of bait delivery interval in an automated head-chamber system on respiration gas estimates when cattle are grazing rangeland. Professional Animal Scientist. 33(4):490-497. https://doi.org/10.15232/pas.2016-01593.
Interpretive Summary: Methane and carbon dioxide represent 11 and 81%, respectively, of all man-made greenhouse gas emissions. Agricultural methane emissions account for approximately 43% of all man-made methane emissions and most agricultural methane emissions are attributed to ruminal fermentation of feedstuffs within animal. Hence, there is significant interest in quantifying and mitigating this source from ruminant livestock. The automated head-chamber system (AHCS; GreenFeed, C-Lock, Inc., Rapid City, SD) evaluated here can be placed in a pasture with grazing cattle and can measure their methane and carbon dioxide emissions and these data can then be used to parameterize and validate greenhouse gas emission models. However, improper management of the AHCS can have a significant effect on emission estimates. How the AHCS attracts the cattle to place their head in the chamber is by providing small discrete portions of palatable feed, referred to as bait. One factor affecting the quality of emission estimates is the amount of time the animal hold its muzzle in front of the intake manifold when the AHCS is measuring emissions. This time variable can be manipulated by the number and rate that bait is delivered while the calf has its head in the chamber. In 2 experiments bait-delivery rate was set to 4 discrete times in order to change the time the animal has its head is in the AHCS (18 to 43 second between bait deliveries). These 2 experiments showed that cattle did not respond consistently to increasing time increment for bait delivery and had minimal effect on gas emission estimates, hence timing of bait-delivery rate can be set to accommodate optional visitation by the cattle without negatively impacting emission estimates.
Technical Abstract: Agricultural methane emissions account for approximately 43% of all anthropogenic methane emissions and the majority of agricultural CH4 emissions are attributed to enteric fermentation within ruminant livestock, therefor interest is heightened in quantifying and mitigating this source. An automated head-chamber system (AHCS; GreenFeed, C-Lock, Inc., Rapid City, SD), evaluated here, can be placed in a pasture with grazing cattle and measure their methane and carbon dioxide emissions, and oxygen 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 time an animal has its muzzle in front of the intake manifold for sampling. At each visit, an electronic ear tag triggers the delivery of 6-mm alfalfa pellets (bait; 32-g increments) at timed intervals up to 8 times/visit and a maximum of 4 sampling events/day. In Experiment 1, the AHCS was programmed to deliver feed at 18 (n = 2), 21 (n = 4), 24 (n = 4), and 27 (n = 3) second intervals for 73 days; in Experiment 2 the AHCS was programmed to deliver feed at 19 (n = 2), 27 (n = 4), 35 (n = 4), and 43 (n = 3) second intervals for 43 days. The AHCS was programmed to measure methane, carbon dioxide, and oxygen (Experiment 2 only) fluxes at each visit during the experiments. Time intervals were analyzed by analysis of variance and least-square means were compared using linear and quadratic contrast. Carbon dioxide emitted was not affected (P = 0.11) by time interval in either experiment. Methane emitted and the ratio of methane/carbon dioxide was linearly decreased (P < 0.01) by increasing time increment in Experiment 1, but not different (P = 0.64) in Experiment 2. Further, time increment did not affect oxygen consumption in Experiment 2. Increasing the time increment increased (P < 0.01) the time cattle spent in the AHCS, but did not affect (P = 0.15) the amount of bait consumed. Cattle did not respond consistently to increasing time increment for bait delivery and had minimal effect on gas emission and consumption estimates.