Validation of the sulphur hexafluoride (SF₆) tracer gas technique for measurement of methane and carbon dioxide production by cattle

Abstract

Methane (CH 4 ) and carbon dioxide (CO 2 ) production from six crossbred yearling beef heifers (400 ± 13.0 kg) were measured, using the sulphur hexafluoride (SF 6 ) tracer gas technique (Tracer) and open-circuit hood calorimetry (Cal) to validate the former in estimating rumen CH 4 and CO 2 production in the field. Animals were individually fed a diet consisting of 50% barley concentrate and 50% alfalfa cubes at 1.3 &times ;maintenance requirements daily. Hifers were divided into two groups for individual animal 24- h gas measurements by each method. Each group of heifers was rotated between the Cal and Tracer techniques for 6 consecutive days in an incomplete block design. Methane production ranged from 108 to 145 L d -1 (mean 130 ± 4.0 L d -1 ) using the Cal technique, and 90 to 167 L d -1 (mean 137 ± 4.0 L d -1 ) using the Tracer technique. The mean CH 4 production (L d -1 ) was not different (P = 0.24) between the two methods. Carbon dioxide production with the Tracer technique was 20% higher than CO 2 production with the Cal technique (P < 0.01). The range of CO 2 production was 1574 to 2049 L d -1 (mean 1892 ± 74.0 L d -1 ) by Cal, and 1541 to 3330 L d -1 (mean 2353 ± 74.0 L d -1 ) by Tracer. Day-to-day variation in CH 4 production was not different within each method (P > 0.05); however, animal-to-animal variation (11.7%) was significant for the Tracer technique (P = 0.04), but not for the Cal technique (P = 0.53). Comparison of the equality of variance between the two methods showed that there were no differences in variations (P > 0.05) between Cal and Tracer for CH 4 production. On the other hand, variations in CO 2 production were not equal (P > 0.05) between methods. Day-to-day variation in CO 2 production was significant using Cal, but not Tracer (P > 0.05). Animal-to-animal variation in CO 2 production was 1.6 and 11.8% by Cal and Tracer techniques, respectively. It can be concluded that the SF 6 tracer technique accurately estimated rumen CH 4 production, but CO 2 production was 20% higher. The study suggests that for CH 4 measurements using the SF 6 tracer technique, more animal numbers are needed than for Cal to reduce animal-to-animal variation. Key words: Methane, carbon dioxide, SF 6 tracer technique, validation, cattle