Methane is a potent greenhouse gas. In Australia, only about 11% of national emissions of methane are produced by sheep and cattle, but enteric methane emissions attract media attention and a disproportionate and undeserved amount of blame for global warming is directed at ruminant livestock. Media fascination with 'animal farts' and enteric methane has in turn helped to generate negative social perceptions of the red meat industries. Some strategies for reducing enteric methane emissions and arguments that could help redress these negative perceptions are included in an Appendix to this report. After 2015, calculations of methane emissions from ruminants may be included in carbon accounting schemes and, if this occurs, will place financial imposts on the grazing industry. Proposed methodologies that could be used to measure methane emissions from livestock in Australia are considered along with inventory systems in overseas countries. Current knowledge of the microbiology and biochemistry of the rumen and the reasons why methane is produced by ruminants are reviewed, along with proven and potential ways to reduce methane outputs at an individual animal, or farm, or national level. Currently available strategies that reduce methane emissions are described, along with potential strategies that need further research and development.

Sheep selected for high wool growth were previously shown to exhibit higher microbial protein outflow from the rumen and higher uptake of amino nitrogen in portal blood than those selected for low wool growth. This suggests that genetic selection for wool growth may induce changes in foregut physiology. This study was undertaken to determine whether differences in digesta kinetics, especially mean retention mime (MRT), are associated with differences in fleece production between sheep with low or high estimated breeding values (EBVs) for fleece weight. Twenty mature Merino wethers with uniform EBVs for liveweight were allocated to two groups of 10 animals on the basis of high or low EBVs for yearling fleece weight. Five sheep with low-EBVs and five sheep with high-EBVs for fleece weight groups were allocated in a crossover design to low and high feeding-level treatments, which comprised a blended hay diet fed at maintenance or 1.5 times maintenance. All sheep were given single doses of chromium-mordanted fibre and cobalt-EDTA as inert, non-digestible markers. Digesta kinetics was determined by analysis of the faecal marker excretion patterns using a compartmental model. Higher feed intakes from animals fed 1.5 times maintenance were associated with higher rates of wool growth and higher masses of indigestible fibre in the gut, but reduced MRT of digesta. Although sheep with higher EBVs for fleece weight had higher wool growth rates, there was no indication that these wool growth differences were associated with differences in digesta kinetics. The lack of interaction between feeding level and genotype suggests that MRT did not contribute to genotype differences in wool growth in sheep fed restricted intakes. The differences in wool growth among commercial Merino sheep with divergent fleece weight EBVs achieved by multi-trait selection are not attributable to differences in digesta kinetics, at least when feed is not available 'ad libitum'.

Triticale will become an increasingly important cereal grain in some areas because of its high yield potential, drought stress tolerance and disease resistance (Todorov, 1988). However, it is important to assess the nutritive value of the grain in order to establish its potential as an energy source. The concentrations of nutrients and antinutritive factors in some of the new high-yielding cultivars are also variable and need to be documented. The next level of research will be to determine the nutritive value of these cultivars including the availability of energy in these grains. The present study was conducted to investigate the effect of high-yielding cultivars of triticale in diets on production performance and utilization of dietary energy by broiler chickens.

Rates of methane (CH4) production and the sources of carbon (C) for its synthesis were studied in four mature ewes when dosed with a CH 4-mitigating ionophore ICI-111075, or monensin, or when untreated. The sheep were given 700 g/day of chaffed lucerne hay in equal portions every hour, before and during experiments in which 14C-labelled NaHCO3-, acetate, propionate, lactate and formate were infused intraruminally over 12 h and the specific radioactivity of C (SR) in each of these substrates was determined. During these infusions, the SR of material in the primary pool (the tracer infusion site) and in secondary metabolites of this material (secondary pools) approached asymptotic or 'plateau' values. The rate of infusion of 14CH4 (kBq/day) divided by the plateau SR value (kBq/g C) gave estimates of the rate of irreversible loss of CH4 (g C/day). These calculations indicated that CH4 production rate was reduced by 72% when sheep were dosed with ICI-111075 and by 58% when dosed with monensin. With monensin, the reduction in CH4 production was not associated with hydrogen (H2) accumulation in the rumen headspace gases whereas with ICI-111075, the decrease in CH4 production was associated with marked H2 accumulation in the headspace gases. When plateau SR were attained during the tracer infusions, the percentage ratio, (SR in any secondary pool: SR in the primary pool) gave an estimate of the fraction of C in that secondary pool derived from material of the primary pool. Calculated in this way, the percentage of CH4-C derived from rumen fluid carbon dioxide (CO 2) averaged 59% in untreated sheep, and when sheep were dosed with ICI-111075, the corresponding percentage averaged 12%. These findings indicate there are sources of C for rumen CH4 synthesis other than rumen fluid CO2. However, there was no evidence that C from acetate, propionate, lactate or formate in rumen fluid were direct sources of the unidentified CH4-C. One plausible explanation for these findings is that CH 4 is synthesised within naturally occurring microbial biofilms (attached to feed particles or the rumen wall) from CO2 that is produced locally by fermentation of unlabelled substrates within the biofilms. It is postulated that such pools of CO2 would be kinetically distinct and, during the infusion of 14C-labelled substrates, would exhibit a lower SR than the CO2 in the surrounding rumen fluid.