Enteric methane and carbon dioxide emissions measured using respiration chambers, the sulfur hexafluoride tracer technique, and a GreenFeed head-chamber system from beef heifers fed alfalfa silage at three allowances and four feeding frequencies

摘要

The objective of this study was to determine methane (CH4) and carbon dioxide (CO2) emissions from 8 beef heifers (approximately 20 mo of age and 382 +/- 24.3 kg BW) measured by respiration chambers and the sulfur hexafluoride (SF6) tracer technique and a mobile head-chamber, spot-sampling system (GreenFeed; C-Lock Inc., Rapid City, SD) when fed alfalfa silage at 3 feeding levels and 4 feeding frequencies. Feeding frequency may affect CH4 yield (g/kg DMI), and measurement systems (such as GreenFeed or SF6) are needed to obtain accurate estimates of CH4 emissions from individual cattle under grazing where new pasture is provided once or twice daily. The Hereford x Friesian heifers were used in 5 consecutive periods (P1 to P5) of 14 d with CH4 and CO2 emissions measured with the SF6 technique in wk 1 (5-6 d), with chambers in wk 2 (2 d), and with the GreenFeed system when not in chambers (8 d) of each period. Alfalfa silage was restricted to 6, 8, 8, and 8 kg DM/d in P1, P2, P3, and P4, respectively, and provided ad libitum (10.9-12.2 kg DM/d) in P5. Silage was fed in 2, 2, 3, and 4 meals per day in P1, P2, P3, and P4, respectively, and was continuously available (refilled twice daily) in P5. Methane production increased from 141 to 265 g/d as DMI doubled (P 0.001), but average CH4 yields measured in respiration chambers (24.5 g/kg DMI) and by the SF6 technique (22.8 g CH4/kg DMI) and the GreenFeed system (26.2 g/kg DMI) were unaffected by feeding management (P = 0.6 for chambers and SF6 and P = 0.06 for GreenFeed). The CH4 yields estimated by the GreenFeed system did not differ from CH4 yields estimated by the chambers in P1, P2, P3, and P5 but were greater (P 0.02) than CH4 yields estimated by the SF6 technique in P2, P3, P4, and P5. Yields of CO2 (g/kg DMI) decreased with increasing DMI (P 0.04) and CO2 production (g/d) increased from 5,293 to 9,167 g/d as DMI increased (P 0.001). In general, the SF6 technique and the GreenFeed system provided means for CH4 yield that were not different from those of respiration chambers, and CH4 yields (g/kg DMI) were unaffected by DMI level or feeding frequency.