Selection of sheep with low enteric methane (CH4) emissions is a greenhouse gas (GHG) mifigallon option suitable for pastoral systems. However, the effect of breeding sheep with low enteric CH4 emissions on excreta output and associated CH4 and nitrous oxide (N2O) emissions and therefore total GHG emissions are not known. The objective of the current experiments were to determine excreta output, and estimate associated GHG emissions, from progeny of low and high enteric CH4 per unit of dry matter intake (DMI) selection line sheep (CH4/DMI). The animals were fed two qualifies of cut perennial ryegrass-based pasture (very mature vs. vegetative, 12 animals per CH4/DMI line) in Exp. 1 and cut pasture in two repeated seasons (autumn and winter; 15 animals per CH4/DMI line x 2 seasons) in Exp. 2. Total faecal and urine output was determined on individual animals, followed by enteric CH4 emission measurements in respiration chambers. GHG emissions from urine (N2O) and faeces (CH4 and N2O) were estimated based on New Zealand Agricultural GHG Inventory methodology. There was no interaction between CH4/ DMI selection line and diet quality in Exp. 1 or seasons in Exp.2. Total daily faecal output of DM, organic matter (OM) and neutral detergent fibre (NDF; all g/d) and associated calculated faecal CH4 emissions were greater for low compared to high CH4/DMI sheep in Exp. 1 (P < 0.05), while being similar between CH4/DMI selection lines in Exp. 2. Nitrogen (N) excretion and N partitioning into urine, faeces and body retention, and calculated excreta N emissions, were mostly similar between CH4/DMI selection line sheep in both experiments. Except, faecal N output (g/d and per unit of N intake) and associated calculated direct faecal N2O-N emissions (g/d) were greater in low compared to high CH4/DMI sheep in Exp. 1 (P < 0.05). Enteric CH4 emissions were numerically 8% less (P = 0.15) in Exp.1 and 10% less (P = 0.004) in Exp. 2 and total animal level GHG emissions (CH4 and N2O) were numerically 7% less (P = 0.21) in Exp. 1 and 8% less (P = 0.006) in Exp.2 for progeny of the low compared to the high CH4/DMI line sheep. In conclusion, the magnitude of difference in enteric CH4 (expressed as CO2 -equivalent) between low and high CH4/DMI selection line sheep were still present when CH4 from faeces and N2O emissions from urine and faeces were also accounted for. The animal genetic traits were expressed independent of environmental factors, i.e. pasture quality and season.

Selection lines of sheep with low and high CH yield (g/kg DMI; CH/DMI) are being developed on the basis of feeding pelleted alfalfa hay at 2.0 times maintenance ME requirements in respiration chambers, but their divergence under predominant grazing conditions, as in New Zealand, is not known. The objectives of this study were to determine CH emissions and rumen fermentation characteristics in sheep from low and high CH/DMI selection lines while grazing pasture. Two grazing experiments were conducted with 42 selection line ewes in March 2013 (Exp. 1) and 98 selection line progeny ewe hoggets in October/November 2014 (Exp. 2), with CH emissions estimated by the SF tracer technique and DMI estimated by titanium oxide in combination with natural long-chain -alkanes. Total daily CH production (g/d) was similar between high and low CH/DMI selection line sheep in Exp. 1 and lower for low CH/DMI progeny compared with high CH/DMI progeny in Exp. 2 ( < 0.05). The CH/DMI tended to be 20% lower for low CH/DMI line sheep compared with high CH/DMI selection line sheep in Exp. 1 ( < 0.10) and was 15% lower for the low CH/DMI line in Exp. 2 ( < 0.01). Total VFA concentration and concentrations (m) of acetate, butyrate, and isobutyrate plus isovalerate were lower ( < 0.05) for low CH/DMI line sheep compared with high CH/DMI selection line sheep in both experiments. The current study indicates that differences in CH/DMI and VFA concentrations in selection line sheep, previously established on alfalfa pellets, are also present to a similar magnitude when grazing pasture.

Effects of canola oil spraying on feed intake, ruminal volatile fatty acids (VFA) concentrations and methane (CH4) emissions were investigated in cattle grazing a temperate pasture. Sixty 1-yr-old crossbred steers were allocated into two groups (n=30/group), balanced for body weight (293.8±14.0kg). Following acclimatisation the groups were randomly assigned to one of the two grazing treatments: daily grazing pasture strips (0.1ha) sprayed daily with canola oil (Oil-spray, 12L/strip) and no oil sprayed (Control). The experimental phase involved two periods (Period 1 and 2), for which a paddock of perennial ryegrass (Lolium perenne) was subdivided by electric fences into 0.1ha strips. Period 1 lasted 5 days, whereas Period 2 lasted 12 days. Treatments were applied only in Period 2. Methane emissions were measured using the SF6 tracer technique over 3 days in Period 1 (baseline emissions) and over 4 days in Period 2. Individual animals' feed dry matter intake (DMI) were estimated only in Period 2 using TiO2 as faecal output marker and in vitro digestibility of forage dry matter (IVDMD). Concentrations of VFA in rumen fluid were determined in samples collected at the end of the study by stomach-tubing. Baseline CH4 emissions did not differ between the cattle groups. In Period 2, the herbage eaten by cattle on Oil-spray treatment had higher fat content than on Control (8.9 vs. 3.9% of DM), with no apparent difference in other chemical entities. Cattle grazed on Oil-spray pasture had higher (P=0.02) DMI than those on Control pasture (8.29 vs. 7.51kg/d). Methane emissions from cattle on Oil-spray treatment were lower (P<0.01) than those on Control pasture both on gross (138.6 vs. 156.1g/d) and per unit of feed intake (17.2 vs. 20.9g/kg DMI) basis. Oil spraying of pasture resulted in lower (P<0.001) acetate/propionate ratio in rumen fluid compared to Control pasture (4.2 vs. 5.1). It is concluded that enhanced dietary lipids contents is an effective means of reducing CH4 emissions from grazed pasture. Longer term evaluation of oil supplementation effects on CH4 emission and feeding value of grazed herbages may aid in defining forage breeding avenues targeting lipid content of forage species.

The objective of this study was to determine the genetic parameters of methane (CH4) emissions and their genetic correlations with key production traits. The trial measured the CH4 emissions, at 5-min intervals, from 1225 sheep placed in respiration chambers for 2 days, with repeat measurements 2 weeks later for another 2 days. They were fed in the chambers, based on live weight, a pelleted lucerne ration at 2.0 times estimated maintenance requirements. Methane outputs were calculated for g CH4/day and g CH4/kg dry matter intake (DMI) for each of the 4 days. Single trait models were used to obtain estimates of heritability and repeatability. Heritability of g CH4/day was 0.29 ± 0.05, and for g CH4/kg DMI 0.13 ± 0.03. Repeatability between measurements 14 days apart were 0.55 ± 0.02 and 0.26 ± 0.02, for the two traits. The genetic and phenotypic correlations of CH4 outputs with various production traits (weaning weight, live weight at 8 months of age, dag score, muscle depth and fleece weight at 12 months of age) measured in the first year of life, were estimated using bivariate models. With the exception of fleece weight, correlations were weak and not significantly different from zero for the g CH4/kg DMI trait. For fleece weight the phenotypic and genetic correlation estimates were −0.08 ± 0.03 and −0.32 ± 0.11 suggesting a low economically favourable relationship. These results indicate that there is genetic variation between animals for CH4 emission traits even after adjustment for feed intake and that these traits are repeatable. Current work includes the establishment of selection lines from these animals to investigate the physiological, microbial and anatomical changes, coupled with investigations into shorter and alternative CH4 emission measurement and breeding value estimation techniques; including genomic selection.

Globally, ruminants are the most important source of emission of methane (CH4). Animal-to-animal variation in CH4 emission has genetic basis (Pinares-Patino et al., 2011), hence offering a potential mitigation avenue through animal breeding. However, for this approach to progress to practical application a rapid and reliable method of ranking animals for their CH4 emissions is required. Microbial fermentation of feed in the rumen produces volatile fatty acids (VFA), hydrogen (H2), carbon dioxide (CO2), ammonia and heat. A last step in the process is the reduction of CO2 to CH4 by Archaea using H2 as a source of energy. Formation of both acetic and butyric acids is accompanied by the production of H2 and CO2, whereas propionic production involves a net uptake of H2, hence VFA profiles may be used to predict CH4 emission rates (Benchaar et al., 2001). This controlled study conducted with sheep explored the relationship between rumen VFA and CH4 emission.

Attempts to evaluate the sulphur hexafluoride (SF6) tracer technique to estimate CH4 emissions from ruminants have yielded mixed results. These studies either used SF6 permeation tubes with a long history of use in animals, involved small number of animals or used partial animal enclosure. Our study was conducted with a relatively large number of experimental sheep and controlled variables regarding the permeation rate (PR) of SF6. Twenty four sheep housed in a covered yard and fed lucerne silage to achieve common feed intakes among individuals in the study were administered fresh SF6 permeation tubes. Following 10 d acclimatisation in pens, sheep were staggered in 3 groups of 8 each in order to match availability of 8 respiration chambers. Each group were transferred to individual metabolic crates and habituated to breath collection harnesses for 3d before breath samples were collected daily over 6 consecutive d for CH4 emission estimation using the SF6 'Tracer' technique. Sheep were then brought into respiration chambers for CH4 measurements over 4 consecutive d ('Chamber'). During sheep occupation, chamber inlet and outlet gas streams were sampled into evacuated yokes, as for the tracer technique procedures. Samples were analysed for CH4 and SF6 mixing ratios by gas chromatography as for the Tracer technique, which were then used to estimate CH4 emissions using tracer technique procedures (i.e., Tracer in chamber). Paired t-tests based on within sheep data were used for pairwise comparisons of CH4 emission estimates between techniques. Daily CH4 emissions for the Tracer. Chamber and Tracer in chamber procedures were 14.8 +/- 2.4, 13.9 +/- 1 and 16.1 +/- 2.8 g, respectively. Although Tracer and Chamber emission estimates did not differ, Tracer estimates were associated with much larger among- and within-animal variability than Chamber values, and the relationship between Chamber and Tracer estimates was poor. Rate of recovery of SF6 from chamber gases calculated by dividing the calculated daily emission of SF6 (i.e., net mixing ratio of SF6 x chamber ventilation rate) by the known PR of SF6 was 10% lower than that for CH4. In sheep, the average CH4 emission estimate using the SF6 tracer technique matches that obtained from chambers, but the correlation between estimates is poor, possibly due to a mismatch in routes of excretion of tracer and trace gases.This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. (C) 2011 Elsevier B.V. All rights reserved.