Climate change presents a range of challenges for animal agriculture in Australia. Livestock production will be affected by changes in temperature and water availability through impacts on pasture and forage crop quantity and quality, feed-grain production and price, and disease and pest distributions. This paper provides an overview of these impacts and the broader effects on landscape functionality, with a focus on recent research on effects of increasing temperature, changing rainfall patterns, and increased climate variability on animal health, growth, and reproduction, including through heat stress, and potential adaptation strategies. The rate of adoption of adaptation strategies by livestock producers will depend on perceptions of the uncertainty in projected climate and regional-scale impacts and associated risk. However, management changes adopted by farmers in parts of Australia during recent extended drought and associated heatwaves, trends consistent with long-term predicted climate patterns, provide some insights into the capacity for practical adaptation strategies. Animal production systems will also be significantly affected by climate change policy and national targets to address greenhouse gas emissions, since livestock are estimated to contribute ~10% of Australia's total emissions and 8-11% of global emissions, with additional farm emissions associated with activities such as feed production. More than two-thirds of emissions are attributed to ruminant animals. This paper discusses the challenges and opportunities facing livestock industries in Australia in adapting to and mitigating climate change. It examines the research needed to better define practical options to reduce the emissions intensity of livestock products, enhance adaptation opportunities, and support the continued contribution of animal agriculture to Australia's economy, environment, and regional communities.

Improvements in feed conversion efficiency (FCE) can be applied to individual animals as well as to production from land, as in a farm system. Our focus relates mainly to food production from individual animals within any animal population where there is divergence in the efficiency that individuals use ingested feed for maintenance and production; primarily due to differences in digestion and metabolism. Intake variation from the predicted mean for individuals of a similar size and level of production in a population has been termed residual feed intake (RFI), with low values indicating an efficient animal. Efficient animals require less feed than average and can be expected to produce less CH₄ and N₂O per unit product than the population average at a similar level of production. Selection for this trait will lower CH₄ emissions per animal, unless more animals are kept to eat the feed not required by efficient animals. There are few published evaluations of CH₄ yields from animals with divergent RFI and there is little evidence that efficient animals have a different CH₄ yield expressed as CH₄/kg dry matter (DM) intake. Of equal or greater importance than RFI is the need to select high producing animals, as this will reduce emissions/unit of product, referred to as emissions intensity (Ei). Research should identify productive individuals that have a low RFI to minimise Ei and maintain food production. The extent to which CH₄ can be reduced by selection for RFI will depend on the heritability of efficiency, dispersal of efficient animals through all populations and their resilience in a production system (i.e., robustness). The benefit of RFI to lowering greenhouse gas (GHG) emissions is its application, irrespective of farming system (i.e., confined, intensive, extensive grazing), especially because efficient animals are likely to increase farm profitability. Efficient animals are already in all herds and flocks and research must identify and remove inefficient individuals, while retaining and ensuring efficient ones are fit to purpose. However, the biggest benefits to reducing emissions and increasing production will be associated with good animal management practice (e.g., appropriate genetics, reproductive performance, longevity) with efficient animals superimposed. Good animal systems management will improve profitability, and apply to both intensive and extensive systems to increase food production and lower Ei. One dilemma for agriculturists will be the practice of feeding grains to ruminants, as gains in animal efficiency, especially in reduction of Ei, are likely to be biggest with high energy density rations, but feeding grain to ruminants may become an unsustainable practice if food supplies for humans are limited.

The purpose of this study was to determine if estimated breeding value (EBV) of an animal's sire and or the animal's nutrition affected the structure of its 'M. longissimus thoracis et lumborum' (LL) and, hence, the eating quality of meat derived from its carcass. Lambs were chosen based on the EBV of their sires in terms of post-weaning live weight (PWWT), post weaning fat at the C-site (PFAT), and post-weaning eye muscle depth (PEMD). Morphometric techniques were used to characterise muscle structure in terms of the distribution of intramuscular connective tissue; the variables together are called fascicular structure. Perimysial seam thickness and fascicular width were both influenced by sire estimated breeding values for PWWT, PFAT, and PEMD. Variation in fascicular structure was associated with an interaction between PEMD-EBV and PFAT-EBV of the sire. Fascicular width decreased with increased PEMD-EBV and increased with PFAT-EBV, but was not affected by PWWT-EBV. When the total seam thickness was adjusted to a common fascicular width, the lambs on a low plane of nutrition had relatively more intramuscular connective tissue than those on a high plane. The total seam thickness was negatively associated with PFAT-EBV and positively associated with PEMD-EBV. Warner Bratzler shear (WBS) peak force (PF) and initial yield were not associated with differences in sire EBV. The residual WBS shear force, peak force minus initial yield (PFIY), and compression values were negatively associated with nutrition but were positively associated with PWWT-EBV and PEMD-EBV of the sires. These latter 2 effects were moderated by nutrition. The data support the hypothesis that morphological characteristics of perimysium are genetically determined and nutritionally responsive. Variance in morphology accounted for some variance in the biophysical attributes of meat and may help explain why sheep with high muscling potential have tougher meat.

The objective of this study was to establish the extent to which lamb myofibre characteristics at ~8 months of age were influenced by sire (n = 9) estimated breeding values (EBVs) and pasture-based nutritional systems (low and high quality and availability, LOW and HIGH) from birth to slaughter (n = 56). Immunostaining of myosin heavy chain isoforms in 'longissimus' muscle fibres revealed that as the post-weaning eye muscle depth EBV (PEMD) increased, the percentage of type 2B/X myofibres increased and the percentage of type 2A myofibres decreased. The percentage of type 2B/X myofibres also increased with increasing PEMD in the 'semimembranosus' muscle, but not in the 'semitendinosus' muscle. Post-weaning fat depth (PFAT) EBV was negatively related with the percentage of type 2B/X myofibres in 'longissimus' and 'semitendinosus' muscles and with the relative area of more glycolytic to more oxidative fibre types, although there was an interaction with nutritional system in the 'semitendinosus' muscle, with this ratio increasing with the PFAT EBV among the LOW nutrition lambs. Overall, post-weaning weight (PWWT) EBV had less effect on myofibre characteristics than PEMD and PFAT EBVs. Average cross-sectional area of myofibres was more affected by the LOW than HIGH nutritional system in 'longissimus' muscle (-25%) compared with 'semitendinosus' (-21%) and 'semimembranosus' (-15%) muscles. LOW nutrition resulted in a significantly smaller cross-sectional area of all myofibre types in 'longissimus' muscle and of types 2A, 2AB/X, and 2B/X in 'semimembranosus' and 'semitendinosus' muscles. Overall, the relative area of glycolytic myofibres increased and/or more oxidative myofibre types decreased in LOW compared with HIGH nutritional system lambs in 'longissimus' and 'semimembranosus', but not in 'semitendinosus' muscle. The results demonstrate significant influences of sire EBVs on myofibre characteristics of lambs, the extent of which depends upon muscle type and nutritional regimen. More specifically, they suggest continued selection for increased muscling and reduced fatness in lambs are associated with shifts in the proportions of myofibre types, with potential for adverse effects on eating quality. They also show that the direction and magnitude of the effects of chronic, moderate postnatal nutritional restriction at pasture on myofibre characteristics vary between muscles with different contractile, metabolic, and/or functional characteristics.

Genetic selection and breeding to reduce methane production is one option to reduce greenhouse gas emissions, but correlated responses in production traits also need to be considered. The objective of this study was to quantify the effect of divergent selection for methane yield (MY), on methane and body weight traits in Angus cattle. High and Low MY selection lines were created in each of two performance-recorded Angus research herds during the 2011 mating season. This study is a preliminary report on the divergence of these selection lines, as assessed by the performance of the 2013 born progeny. There was no significant selection line by herd interaction. Approximately half a generation of selection was achieved. There was a significant (P<0.05) divergence between the two lines in the selected trait, methane yield. This was also reflected in the significant (P<0.05) selection line differences in the residual methane (actual minus expected methane production) traits and also in the estimated breeding values for these traits. There were no significant selection line differences in birth, weaning and yearling weights.

• Simple flock management practises that increase productivity per ewe will also reduce emissions per unit animal-product sold. • The reductions in emissions intensity observed for an individual sheep is typically greater than seen on the farm scale, due to resultant changes in ewe/lamb numbers while feed availability is unchanged.

Records on 1043 young Angus heifer and bull progeny from 73 sires, measured for methane production in respiration chambers, were used to evaluate the accuracy of a 1-day measurement relative to 2-day measurement duration. The traits assessed were dry matter intake (DMI, kg/day), methane-production rate (MPR, g/day), methane yield (MY, MPR per unit DMI) and four residual methane (RMP, g/day) traits. The RMP traits were computed as actual MPR minus expected MPR, where the expected MPR were calculated from three widely used equations. The expected MPR for the fourth RMP trait was computed by regressing MPR on DMI, using the data from the study. Variance components, heritability, phenotypic and genetic correlations, and the efficiency of selection using 1-day compared with 2-day measurement were used as assessment criteria. The environmental variance for the 2-day measurement was slightly lower than that of the 1-day measurement for all the traits studied, indicating that the addition of an extra day of data was effective in reducing the amount of unexplained variation in each trait. However, these minor reductions did not have a major impact on accuracy; hence, very high phenotypic (rp of 0.91-0.99) and genetic (rg of 0.99 for each trait) correlations were obtained between the two measurement durations. The very high genetic correlation between the two durations of measurement indicated that, at the genetic level, the 1-day duration is measuring the same trait as the 2-day measurement duration. Any enteric-methane emission-abatement strategy that seeks to reduce MPR per se, may have a detrimental impact on ruminant productivity through a correlated reduction in feed intake; hence, MY and the RMP traits are likely to be the traits of interest for genetic improvement. Efficiency of selection for MY and the RMP traits ranged from 0.96 to 0.99, which implies that there would be less than 5% loss in efficiency by adopting a 1-day relative to a 2-day methane-measurement duration. While the throughput of the respiration-chamber facility can be increased by adopting a 1-day measurement duration, additional resources, such as holding pens, would be required to take advantage of the extra day.

A total of 2,600 methane (CH4) and 1,847 CO2 measurements of sheep housed for 1 h in portable accumulation chambers (PAC) were recorded at 5 sites from the Australian Sheep CRC Information Nucleus, which was set up to test leading young industry sires for an extensive range of current and novel production traits. The final validated dataset had 2,455 methane records from 2,279 animals, which were the progeny of 187 sires and 1,653 dams with 7,690 animals in the pedigree file. The protocol involved rounding up animals from pasture into a holding paddock before the first measurement on each day and then measuring in groups of up to 16 sheep over the course of the day. Methane emissions declined linearly (with different slopes for each site) with time since the sheep were drafted into the holding area.

Breeding of ruminant livestock for low CH₄ emission is an attractive means of mitigating enteric CH₄ emissions. However success requires that the mechanism responsible for among animal variation in emissions is repeatable and heritable and has a negligible negative impact on production and functional traits. This study was designed to estimate repeatability and heritability of the CH₄4 emission trait in sheep, and to determine whether the ranking of sheep based on their CH₄ emissions is maintained over a range of contrasting diets. A flock of 105 ewe lambs (10 months old) of a progeny testing program were screened for their CH₄ yields (i.e., emissions/unit feed dry matter (DM) intake) when a molasses containing grass silage was fed at restricted intake (1.3 x maintained 13-15 d between consecutive measurements (i.e., screening phase). Mean CH₄ yield of lambs was 18.4 ± 0.38 g/kg DM intake during the screening phase, and estimates of repeatability and heritability for CH₄ yield were 0.16 and 0.30, respectively. Methane yield in the screening phase was 7.9% higher for the high versus low ranked sheep (19.2 ± 0.18 versus 17.8 ± 0.26 g/kg DM intake). The 10 lowest (low rank) and the 10 highest (high rank) CH₄ yielding sheep were selected and retained for further study. Two repeated measurements of CH₄ yield were conducted, the first measurement while sheep were fed fresh cut perennial ryegrass pasture (grass), the second with the same sheep fed a 400:600 concentrate:forage (wheat grain:lucerne hay; fresh basis) pelleted diet (pellet). Repeated measurements revealed that rankings were maintained among diets, but that there was a CH₄ rank x diet interaction for CH₄4 yield. When fed the grass diet, the high ranked sheep had 13% higher CH₄4 yield than the low ranked sheep, but when fed the pelleted diet, the high ranked sheep had 36% higher CH₄ yield than the low ranked sheep. Emissions of hydrogen were only measurable when sheep were fed the pelleted diet. This study is the first to report that ranking of sheep for CH₄4 emissions is consistent among diets, although the magnitude of difference among the rankings was affected by diet, suggesting that among animal variation in CH₄ emission could be exploited to breed animals for low CH₄ emission.

The efficacy of technologies to reduce enteric CH₄ emissions from ruminants are typically evaluated on individual animals with little consideration of enterprise scale impacts. While impacts of the many rumen manipulations being studied are hard to anticipate, there is adequate information to assess impacts of farm management changes and potential animal genetic changes on whole farm productivity and enteric CH₄ emissions. Seven common sheep production systems grazing an annual pasture in central New South Wales, Australia, were modelled using GrassGro® (version 3.1.2). A range of animal management and animal genetic strategies were examined for their impact on total enteric emissions, emission intensity (i.e., kg CO₂ equivalent/kg live weight (LW) of animal sold) and profit. Within enterprises, mitigation options were compared at their respective sustainable economic optimum stocking rate as it was assumed that farmers would seek to achieve the highest sustainable profit achievable from a finite land resource. Management options considered were choice of lambing time, mating ewes for the first time as lambs rather than yearlings, and feeding lambs to reduce time to slaughter. The potential for using selective animal breeding was also tested, with sheep physiological parameters being altered in GrassGro® to represent genetic improvement in fecundity, LW gain, residual feed intake and CH₄ yield. In general, the management choices delivering lowest emission intensity were also the most profitable within sustainability constraints. Mating maiden ewes as lambs was only effective in reducing enterprise emissions intensity in self-replacing flocks (i.e., no purchased replacements). When stocking rates were at the sustainable economic optimum, choice of enterprise or management had little influence on total enteric emissions from the enterprise. If decisions are guided solely by economics, farmers are likely to continue with similar levels of production (and emissions) until a price on enteric CH₄ emissions makes the sheep enterprise unprofitable, or an alternative more profitable enterprise than sheep grazing emerges. Improving animal genetics for residual feed intake or CH₄ yield offers opportunity to reduce enterprise emissions, but industry progress toward higher genetic merit for these traits is expected to be slow due to relatively low heritability and competing economic imperatives for progress in other traits.