A modified sulphur hexafluoride tracer technique enables accurate determination of enteric methane emissions from ruminants

Abstract

a b s t r a c tThe sulphur hexafluoride (SF 6 ) tracer technique enables determination of enteric methane emissions from large numbers of individual ruminant animals. The objective of this research was to identify and correct substantial errors within the SF 6 technique. Six experiments were undertaken using respiration chamber, laboratory or SF 6 techniques. Experiment 1 used respiration chambers to demonstrate that the daily pattern of methane emissions from dairy cows was related to their pattern of feed intake. In contrast, the daily emission of SF 6 from these cows was constant and independent of the pattern of methane emission. This finding supports the contention that in order to accurately determine daily methane emissions using the SF 6 technique, it is necessary that gases are collected continuously at a constant rate for 24 h. Since development of the SF 6 technique in 1993, it has been propounded that capillary-tube flow restrictors achieved a constant rate of sample collection into evacuated gas collection canisters. Laboratory experiments 2, 3, 4 and 5 demonstrated that, when capillary-tube flow restrictors are used, the rate of sample collection declined and caused a bias of up to 15.6% in calculated methane emissions. This error was caused by an interaction between the declining sample collection rate and the pattern of an animal's methane emission over 24 h. In contrast, orifice plate flow restrictors maintained a constant sample collection rate at canister pressures <0.31 atm and thereby minimised the decline in sample collection rate. Experiment 5 also demonstrated that sample collection using orifice plate flow restrictors, combined with initial (<0.03 atm) and final (<0.49 atm) canister pressures, substantially reduced measurement error. Accuracy of the modified SF 6 technique, incorporating orifice plate flow restrictors for 24 h sample collection, was validated in Experiment 6. The mean (S.D.) methane yield (g CH 4 /kg DMI) of eight cows did not differ (P = 0.135) when determined using the modified SF 6 technique 22.3 (1.44) or chambers 21.9 (1.65). In addition, the between-animal coefficient of variation for methane yield determined using the modified SF 6 technique (6.5%) was similar to that determined using

Reducing the carbon footprint of Australian milk production by mitigation of enteric methane emissions

“…Since this workshop, there has been considerable research undertaken in Ireland and Australia to improve the accuracy and reliability of the SF 6 technique (e.g. Williams et al 2011a;Deighton et al 2013aDeighton et al , 2014aDeighton et al , 2014bMoate et al 2014cMoate et al , 2015. This research has identified the source of measurement errors within the SF 6 tracer technique and has led to the development and validation of a modified method .…”

“…A compilation of data from the most recent Australian feeding studies, including seven published experiments Deighton et al 2014b;Williams et al 2014b) and five other unpublished experiments from these authors, provides additional quantification of the lipid effect and, for the first time, quantification of the effect of wheat in the diet, on methane emissions from dairy cows. This dataset included measurements from 362 lactating dairy cows from six experiments in which methane was measured by open-circuit calorimeters and six experiments in which methane was measured by the SF 6 technique (Williams et al 2011a;Deighton et al 2014b).…”

“…However, there have been three Australian experiments in which cows have been fed measured amounts of harvested pasture (without supplement) and their mean methane emissions ranged from 369 to 458 g CH 4 /cow.day, methane yields ranged between 21.9 and 24.6 g CH 4 /kg DMI and PEMI ranged between 15.1 and 18.3 g CH 4 /kg milk Deighton et al 2014b;Moate et al 2014a). These methaneemission metrics are similar to those reported from pasture-fed dairy cows in other countries.…”

“…This dataset included measurements from 362 lactating dairy cows from six experiments in which methane was measured by open-circuit calorimeters and six experiments in which methane was measured by the SF 6 technique (Williams et al 2011a;Deighton et al 2014b). In these experiments, cows were in various stages of lactation and consumed diets containing a diverse range of dietary ingredients.…”

Methane emissions from two breeds of beef cows offered diets containing barley straw with either grass silage or brewers’ grains

“…Based on the potential for differences in animal physiology or behaviour to influence CH 4 production, a number of recent studies have been conducted within outdoor grazing environments to examine CH 4 emissions from breeds, which are suited to extensive grazing systems compared with more intensively managed breeds selected for increased growth and carcass yields. Measurements of CH 4 in grazing environments are possible using the SF6 tracer technique (Deighton et al, 2014). In the studies of Fraser et al (2014) and Richmond et al (2015), where two breeds were studied on two pasture types (lowland v. upland pasture), no difference between breeds (or interactions with pasture type) were identified for CH 4 expressed on a daily, DMI or GEI basis.…”