Sheep (Ovis aries) represent one of the most important livestock species for global animal protein and wool production. However, little is known about the genetic and biological basis of ovine phenotypes, particularly those with high economic value and environmental impact. Here, by integrating 1413 RNA sequencing (RNA-seq) samples from 51 distinct tissues across 14 developmental time points, representing early-prenatal, late-prenatal, neonatal, lamb, juvenile, adult, and elderly stages, we constructed a high-resolution Developmental Gene Expression Atlas (dGEA) in sheep. We observed dynamic patterns of gene expression and regulatory networks across tissues and developmental stages. Leveraging this resource to interpret genetic associations for 48 monogenic and 12 complex traits in sheep, we found that genes upregulated at prenatal developmental stages played more important roles in shaping these phenotypes than those upregulated at postnatal stages. For instance, genetic associations of crimp number, mean staple length (MSL), and individual birthweight were significantly enriched in the prenatal rather than postnatal skin and immune tissues. By comprehensively integrating genome-wide association study (GWAS) fine-mapping results with the sheep dGEA, we identified several candidate genes for complex traits in sheep, such as SOX9 for MSL, GNRHR for litter size at birth, and PRKDC for live weight. These results provide novel insights into the developmental and molecular architecture of ovine phenotypes. The dGEA (https://sheepdgea.njau.edu.cn/) will serve as an invaluable resource for sheep developmental biology, genetics, genomics, and selective breeding.

Introduction Biochar has gained significant attention as a possible anti-methanogenic supplement for ruminants due to its potential to reduce methane (CH4) emissions from enteric fermentation. However, its effects on rumen methanogenesis have been inconsistent and, in some cases, contradictory. These variations are likely influenced by factors such as the type of biochar used, its source material, and how it is administered, including the form in which it is provided and the dosage needed to achieve desired outcomes. This study aimed to examine the effects of two fit-for-purpose biochars on rumen fermentation, CH4 emissions, and the rumen microbiome of cattle-fed roughage-based diets. Two experiments were conducted to assess the potential of biochar in mitigating CH4 emissions.Experiment 1 This was a controlled pen trial conducted over 56 days, involving 12 steers that were fed Rhodes grass hay ad libitum. The animals were assigned to one of four treatment groups: control (no biochar, only molasses), low dose (50 g biochar/animal/day), mid dose (100 g biochar/animal/day), or high dose (200 g biochar/animal/day). Two types of biochar, Biochar 1 and Biochar 2, were administered with molasses (200 mL per animal/day). Methane emissions were measured using open-circuit respiration chambers, and rumen fluid samples were collected for analysis of the rumen microbial community and fermentation metabolite.Experiment 2 In this trial, 45 heifers were selected and grazed together in a single paddock for 60 days to assess the effects of biochar on productivity and CH4 emissions under grazing conditions. The animals were allocated to one of three treatment groups (15 animals per group): control (no biochar, only molasses), Biochar 1, or Biochar 2. Each group was administered biochar at an estimated single dose of 100 g per animal/day mixed with molasses. Methane emissions were measured using GreenFeed systems in the field to monitor CH4 production from individual animals.Results In the controlled pen trial (Experiment 1), biochar supplementation resulted in a reduction of CH4 emissions by 8.8-12.9% without any negative effects on rumen fermentation or dry matter intake (DMI). Minor changes were observed in the rumen bacterial community, particularly in the Christensenellaceae and Prevotellaceae families. However, in the grazing trial (Experiment 2), no significant differences in CH4 emissions or productivity were detected with biochar supplementation.Conclusion While the results from controlled feeding conditions suggest that biochar has the potential to reduce enteric CH4 emissions, the lack of significant findings under grazing conditions highlights the need for further research. Future studies should focus on identifying biochar types, doses, and delivery methods that are effective in reducing CH4 emissions in grazing systems without compromising cattle productivity.

CONTEXT: The semi-arid mulga lands of the Southern Rangelands of Western Australia experience frequent droughts. Maintaining a profitable animal grazing enterprise whilst preserving rangeland condition requires selecting an appropriate stocking rate and herd structure. OBJECTIVE: We construct and apply bioeconomic models of beef enterprises for the semi-arid Southern Rangelands of Western Australia, to assess the profitability and relative riskiness of three different livestock production systems and three different stocking rates when exposed to different frequencies of drought. METHODS: We construct bio-economic models of herd structures that separately focus on producing either: (i) 200 kg heifers and 210 kg steers (ii) live export of 340 kg heifers and 380 kg steers, or (iii) 500 kg heifers and 560 kg steers for local slaughter. The models are applied to assess the financial and production resilience of each herd structure for three different stocking rates, given the incidence of drought and various price scenarios. RESULTS AND CONCLUSIONS: Comparing the three herd structures, option (iii) produces more kilograms of beef at an equivalent grazing pressure and recovers fastest from drought. Considering cattle prices over the 7-year period ending in 2021, live export and slaughter production systems generate comparable financial returns to graziers' actual reported results. Under two different scenarios of future prices, option (iii) provides the most profitable outcome. Applying a stocking rate that is 66% of a recommended stocking rate allows use of residual rangeland feed (known as 'haystack') during drought, generates greater profit, and produces a more stable herd size and income. Not matching the haystack with the longest modelled drought reduces the grazier's average annual profit by $172,000. The optimum herd structure identified in this study targets the production of 500 kg heifers and 560 kgs steers for local slaughter, and relies on a conservative stocking rate that leaves enough haystack to increase resilience if ever consecutive droughts occur. SIGNIFICANCE: In the Southern Rangelands of Western Australia, there are financial and environmental merits in a herd structure that produces heavy steers and heifers for local slaughter yet is underpinned by conservative stocking rates.

Context Australia is renowned for its climate variation, featuring years with drought and years with floods, which result in significant production and profit variability. Accordingly, to maximise profitability, dryland farming systems need to be dynamically managed in response to unfolding weather conditions. Aims The aim of this study is to identify and quantify optimal tactical livestock management for different weather-years. Methods This study employed a whole-farm optimisation model to analyse a representative mixed enterprise farm located in the Great Southern region of Western Australia. Using this model, we investigated the economic significance of five key livestock management tactics. These included timing of sheep sales, pasture-area adjustments, rotational grazing, crop grazing and sheep nutrition adjustments. Key results The results showed that, on the modelled dryland mixed-enterprise farm in the Great Southern region of Western Australia, short-term adjustments to the overall farm strategy in response to unfolding weather conditions increased expected profit by approximately 16%. Each tactic boosted profit by between A$7704 and A$53,171. However, we outline several complexities that farmers must consider when implementing tactics. Conclusions The financial gains from short-term tactical management highlighted their importance and farmers’ need to develop and apply those skills. The tactical skills promote business resilience and adaptability in the face of climate uncertainties. Implications The study highlighted the economic value of dynamic livestock management in response to climate variations, offering farmers in the Great Southern region the means to underpin profitable and sustainable farm practices.

The trade-off between accuracy and complexity is a common issue faced in farm systems analysis. To provide insights into the importance of representing weather-year sequence in farm modelling, two whole-farm optimisation models are constructed and applied to a mixed enterprise farming system in a subregion of Western Australia. The frameworks are (i) four-stage single-sequence stochastic programming with recourse (4-SPR) to capture weather-year variation and management tactics tailored to each weather-year and (ii) eight-stage multi-sequence stochastic programming with recourse (8-SPR) to outline weather-year sequences and management tactics tailored to particular weather-year sequences. Results show that single-year stochastic programming generates similar expected profit and strategic management as multi-year stochastic programming. However, optimal tactical farm management is affected by the outcome of the previous year. Tactical decision-making in response to the outcome of the preceding weather-year increases profitability by 14%. Technology changes over the last decade, particularly the increase in computer speed and computational power, increase the ease of construction and application of the 4-SPR and 8-SPR frameworks. Nonetheless, choosing which framework is best to apply to a particular issue or opportunity remains a challenge.

Sheep (Ovis aries) represents one of the most important livestock species for animal protein and wool production worldwide. However, little is known about the genetic and biological basis of ovine phenotypes, particularly for those of high economic value and environmental impact. Here, by generating and integrating 1,413 RNA-seq samples from 51 distinct tissues across 14 developmental time points, representing early prenatal, late prenatal, neonate, lamb, juvenile, adult, and elderly stages, we built a high-resolution developmental Gene Expression Atlas (dGEA) in sheep. We observed dynamic patterns of gene expression and regulatory networks across tissues and developmental stages. When harnessing this resource for interpreting genomic associations of 48 monogenetic and 12 complex traits in sheep, we found that genes upregulated at prenatal developmental stages played more important roles in shaping these phenotypes than those upregulated at postnatal stages. For instance, genetic associations of crimp number, mean staple length (MSL), and individual birth weight were significantly enriched in the prenatal rather than postnatal skin and immune tissues. By comprehensively integrating fine-mapping results and the sheep dGEA, we identified several key genes associated with complex traits in sheep, such as SOX9 (associated with MSL), GNRHR (associated with litter size at birth), and PRKDC (associated with live weight). These results provide novel insights into the gene regulatory and developmental architecture underlying ovine phenotypes. The dGEA (https://sheepdgea.njau.edu.cn/) will serve as an invaluable resource for sheep developmental biology, genetics, genomics, and selective breeding. ### Competing Interest Statement The authors have declared no competing interest.

Context Ruminant livestock industries are seeking to improve efficiency of feed use and reduce greenhouse gas emissions. Aims The research aimed to measure variation in feed intake and residual feed intake (RFI) in growing lambs and examine the inter-relationships of related traits and diet effects. Methods In Phase 1, 6-month-old Merino wethers (n = 113) were fed a base diet ad libitum for 60 days to measure dry matter intake (DMI), liveweight (LWT) and average daily gain (ADG). Whilst being fed the same base diet, measures of body composition (using computer tomography scanning) and methane emissions were collected. For Phase 2, lambs selected for low or high RFI in Phase 1 were randomly assigned to either a low or high diet and fed ad libitum for 30 days. They were assessed for intake, growth, body composition and CH4 emissions. Key results In Phase 1 there was significant variation in DMI, which was explained by these traits in order of significance (R2 additive): LWT (R2 = 63.9%), ADG (R2 = 70.4%) and fat gain (R2 = 75.7%). In Phase 2, high RFI lambs had higher metabolisable energy intake (MEI; P < 0.05) compared to low RFI lambs. In lambs fed the high diet, intake (DMI and MEI P < 0.001), LWT (P < 0.05), ADG (P < 0.001), fat and lean gain (P < 0.001) were higher than in lambs fed the low diet. Daily methane emissions were highest (P < 0.05) in high RFI lambs fed the high diet. There were no significant effects of RFI or diet on methane yield (MY; g methane/kg DM). Differences in RFI or RFI adjusted for fat gain did not persist to the end of the 30 day feeding period in Phase 2. Conclusions Lambs with low RFI had lower MEI for the same liveweight as well as lower fat and lean gain in the empty bodyweight. They also had lower daily methane emissions compared to those that had high RFI and ate more. Implications The opportunity to select sheep at a young age with lower RFI and lower MEI is of significant production and environmental importance.

Context Breech strike is a serious disease particularly in wool sheep. Skin wrinkle and dags are known predisposing factors for breech strike, although a large part of the variation between sheep is unexplained. Aims We used sensor buttons to determine whether there were differences in humidity and temperature in the breech area of Merino sheep exposed to blowflies without traditional preventive measures being used in the flock. Methods Sixty-two Merino rams and 62 Merino ewes that had high or low breeding values for breech strike were each fitted with a sensor button to record hourly temperature and humidity in the breech over 49 days. The sensors were fitted before the onset of the blowfly season. The sensor was tied to a wool staple close to the skin in the breech and was removed when a sheep was struck. All remaining buttons were removed prior to shearing. Breech wrinkle, neck wrinkle, breech cover and faecal soiling (dags) were recorded on all the sheep. A total of 98 213 hourly temperature and humidity records were analysed with cubic smoothing splines to assess how humidity and temperature differed between struck and unstruck sheep, and whether the breech indicator traits affect temperature and humidity in the breech. Results Time of day and day-to-day variation prior to being struck explained most of the variation of temperature and humidity in the breech of the sheep. Humidity and temperature increased with an increase in breech cover. The humidity in the breech area was, on average, 2% higher in struck sheep prior to being struck. There was a sharp increase in humidity in struck sheep in the 8 days leading up to detection of breech strike relative to unstruck animals, most probably due to exudate from the wound. Conclusions Sheep prone to be struck have higher humidity in the breech than sheep less prone to be struck. Implications Temperature in the breech does not qualify as a potential indicator trait for breech strike in wool sheep, whereas humidity needs further research to determine its effectiveness as a potential indicator trait.

Context Reducing livestock emissions, the largest single contributor to agricultural emissions, is increasingly recognised as a high priority. The low biological efficiency of beef cattle, due to their long gestation period, long generational interval, and propensity to be uniparous, contributes to the high methane emissions intensity (kg CO2-e/kg product) of beef compared to most other food products. Aims We evaluate the potential of increasing the frequency of multiparous births (twinning) as a pathway to reducing the methane intensity of beef and the net methane emissions of intensive beef systems. Methods We simulate a uniparous herd structure and emissions profile using GrassGro™ livestock systems modelling software and then calculate the effects of an increasing frequency of multiparous births (twinning), up to 1.53 calves per cow joined, on methane emissions. Key results Our results demonstrate that beef from calves reared as twins has a 22% lower methane intensity than beef from a single reared calf. Although twinning reduces the methane intensity of beef, at the herd level, net methane emissions could rise by as much as 23% at 1.53 calves per cow joined if overall herd size is allowed to grow through an increased number of calves. If we decrease stocking rates, whilst also increasing twinning rates, it is possible to reduce net emissions by up to 14%, without changing productivity. Conclusions Our results illustrate the significant potential of twinning to decrease the methane intensity of beef and to increase the productivity per cow in intensive beef systems. Implications Despite this, twinning is unlikely to be a viable net emissions reduction pathway – as twinning will increase stocking rate unless herd structure is altered – unless a commercial or policy driver to reduce net methane emissions is established.

Enteric methane (CH4) emissions from sheep contribute to global greenhouse gas emissions from livestock. However, as already available for dairy and beef cattle, empirical models are needed to predict CH4 emissions from sheep for accounting purposes. The objectives of this study were to: 1) collate an intercontinental database of enteric CH4 emissions from individual sheep; 2) identify the key variables for predicting enteric sheep CH4 absolute production (g/d per animal) and yield [g/kg dry matter intake (DMI)] and their respective relationships; and 3) develop and cross-validate global equations as well as the potential need for age-, diet-, or climatic region-specific equations. The refined intercontinental database included 2,135 individual animal data from 13 countries. Linear CH4 prediction models were developed by incrementally adding variables. A universal CH4 production equation using only DMI led to a root mean square prediction error (RMSPE, % of observed mean) of 25.4% and an RMSPE-standard deviation ratio (RSR) of 0.69. Universal equations that, in addition to DMI, also included body weight (DMI + BW), and organic matter digestibility (DMI + OMD + BW) improved the prediction performance further (RSR, 0.62 and 0.60), whereas diet composition variables had negligible effects. These universal equations had lower prediction error than the extant IPCC 2019 equations. Developing age-specific models for adult sheep (>1-year-old) including DMI alone (RSR = 0.66) or in combination with rumen propionate molar proportion (for research of more refined purposes) substantially improved prediction performance (RSR = 0.57) on a smaller dataset. On the contrary, for young sheep (<1-year-old), the universal models could be applied, instead of age-specific models, if DMI and BW were included. Universal models showed similar prediction performances to the diet- and region-specific models. However, optimal prediction equations led to different regression coefficients (i.e. intercepts and slopes) for universal, age-specific, diet-specific, and region-specific models with predictive implications. Equations for CH4 yield led to low prediction performances, with DMI being negatively and BW and OMD positively correlated with CH4 yield. In conclusion, predicting sheep CH4 production requires information on DMI and prediction accuracy will improve national and global inventories if separate equations for young and adult sheep are used with the additional variables BW, OMD and rumen propionate proportion. Appropriate universal equations can be used to predict CH4 production from sheep across different diets and climatic conditions.

Tedera is a valuable high-quality forage for sheep during summer–autumn. There is evidence that prior grazing experience of novel forages influences preference and haymaking of tedera improves preference by goats. In the first experiment, it was hypothesised that the voluntary feed intake (VFI) of fresh leaves and stems of tedera by sheep would be greater for experienced vs. naïve sheep. In the second experiment, it was hypothesised that the VFI of naïve sheep fed wilted leaves and stems of tedera would be greater than fresh leaves and stems of tedera. To test these hypotheses, adult Merino sheep were fed seven accessions of tedera, in two outdoor pen feeding experiments conducted consecutively. Each of six pens had 14 feeders, two for each accession, and two sheep. In experiment 1, three pens had sheep that had previously grazed tedera (experienced) and three pens had sheep with no experience (naïve), and all were fed fresh leaves and stems of the seven tedera accessions. Experiment 2 involved only naïve sheep, with three pens fed fresh leaves and stems and three pens fed wilted leaves and stems of the seven tedera accessions. Preference was measured each day for six days in experiment 1; and for five days in experiment 2 by calculating the average differences of feed offered and feed remaining from the feeders. In experiment 1, experienced sheep showed no difference in preference (average percentage eaten) in the first hour of each day compared to naïve sheep (70% vs. 56% DM intake (kg), p = 0.27). There was an increase in the amount eaten from the first to the last day for both groups, except for the intake of one accession that was reduced for the experienced sheep. In experiment 2, there was no statistical difference in preference between accessions. However, when the average percentage eaten by the experienced and naïve groups are combined, they are strongly correlated, with significant differences between accessions. Sheep did not eat more wilted tedera compared to fresh, which did not support our hypothesis. The only differences we found in sheep preference for tedera accessions occurred in experiment 1. Further studies to investigate seasonal differences in sheep preference between accessions is required and increased replication is needed to better determine the effect of prior grazing experience on the preference for tedera accessions.

CONTEXTFarm management occurs against a backdrop of weather-year variation. How important is it for farming system models to capture this variation and the management tactics matched to that variation?OBJECTIVEThis study seeks to compare farm optimisation frameworks that differently represent weather-year variation and quantify the value of short-term tactical management in response to unfolding weather conditions.METHODSThree different farm optimisation frameworks that describe a farming system in Western Australia are constructed and compared. The models range from steady-state deterministic programming to complex multi-year stochastic programming with detailed representation of weather-year variation and associated farm management tactics. The models are subject to various applications to test their differences and similarities.RESULTS AND CONCLUSIONSModelling results reveal significant differences in farm profit and optimal farm management when weather-year variation and the relevant management tactics are considered. Including tactical decision-making increases expected farm profit by at least 14%.SIGNIFICANCEThis study demonstrates the usefulness of multi-year discrete stochastic programming when applied to mixed enterprise farm businesses in the Great Southern region of Western Australia. The study quantifies the value of applying farm management tactics in response to weather-year variation and demonstrates that steady-state deterministic, single year stochastic and multi-year stochastic models generate different estimates of profitability and different strategic and tactical management decisions.

The objective of the study was to determine if feeding the probiotic Bacillus amyloliquefaciens strain H57 ('H57 ') to young Merino wethers can improve their feed intake, productivity, energy metabolism and rumen fermentation parameters. Thirty-six Merino wethers were housed in individual pens and fed ad libitum a high-fibre pelleted diet (Control group, n = 18), or the same pelleted diet inoculated with H57 (H57 group, n = 18) for a four-week Treatment period. This was followed by a two-week Carry-over period when all wethers were fed the pelleted diet without H57. Intake of pellets was measured daily (dry matter intake, DMI), live weight (LW) and body condition score (BCS) were measured weekly, and the LW gain (LWG) and feed conversion ratio (FCR) were calculated from the DMI and LWG. During the six-week experimental period, samples of blood and rumen fluid were collected four times and analysed for blood enzymes, metabolites, hormones and rumen fermentation parameters. In the Treatment period, the H57 group had 25% larger final LW than the Control group (6.0 vs 4.8 kg, P = 0.045) and had a greater BCS (2.94 vs 2.44, P = 0.014) and DMI of pellets (1429 vs 1337 g/day, P = 0.033), resulting in a better FCR (6.8:1.0 vs 8.4:1.0, P = 0.049). The increases in final LW and BCS were most marked in the initial two weeks of the Treatment period, but persisted over the remaining two weeks and continued, albeit to a smaller extent, during the Carry-over period. Blood metabolites, enzymes and hormones did not differ between the two groups and were within the expected reference ranges for sheep. Rumen NH3 concentrations were elevated (P = 0.033) in the H57 group throughout the experiment, but overall the volatile fatty acid (VFA) concentrations were not different. B. amyloliquefaciens was present in H57 pellets throughout the Treatment period, and consequently was detected in the rumen fluid and faeces of the H57 group. In conclusion, young Merino wethers fed high-fibre pellets inoculated with H57 for four weeks grew faster, converted the pellets into final LW more efficiently and had a higher BCS than peers fed the same pellets without H57. This can be important when feeding high-fibre pellets to transition young Merino wethers onto a finishing diet. The mechanisms behind these responses remain to be elucidated.

Farm management occurs against a backdrop of weather-year variation. In Australian mixed enterprise farming systems, how important is it for farm optimisation models to capture this variation and the management tactics matched to that variation? This study compares two whole farm optimisation models of an Australian mixed enterprise farming system. One model represents weather-year variation and the short-term tactical management responses tailored to the unfolding weather-year conditions. The other model is a traditional deterministic steady state model that employs the key assumption that every year is an expected weather-year. Both models require the farm manager to select a profit-maximising suite of enterprises and activities relevant to either the expected weather-year or the suite of weather-years that typify weather-year variation where the farm is located. Comparison of the models' results reveals key differences in farm strategy, farm tactics and farm profit. The model that includes tactics aligned to the weather-year variation reveals that tactical decision-making increases expected farm profit by about 18 per cent.

In Australia, 71% of agricultural greenhouse gas (GHG) emissions are enteric methane (CH4), mostly produced by grazing sheep and cattle. Temperate low CH4 yielding legumes and herbs can mitigate enteric CH4 production, but system-level GHG emissions need to be considered. The aims of the study were to: (1) devise a framework to assess GHG reductions when introducing low CH4 yielding species; (2) assess mechanisms of CH4 reduction in temperate legume and herb species for Australia; (3) use a case study to demonstrate expected changes to system-level GHG emissions with the introduction of low CH4 yielding legumes; and (4) identify knowledge gaps and research priorities. Results demonstrate lowering emissions intensity (kg CO2-equivalent/kg product) is crucial to mitigate GHG emissions, but livestock productivity is also important. Several pasture species have anti-methanogenic properties, but responses often vary considerably. Of the species investigated biserrula (Biserrula pelecinus) has great potential to reduce enteric CH4 emissions, but in a case study its emission intensity was similar to subterranean clover (Trifolium subterraneum) but higher than lucerne (Medicago sativa). We conclude that there are temperate legumes and herbs with anti-methanogenic properties, and/or high productivity that could reduce total CH4 emissions and emissions intensity of ruminant livestock production. There is also great diversity in some plant genotypes that can be exploited, and this will be aided by more detailed understanding of plant secondary compounds associated with CH4 reduction. This review suggests an opportunity to formulate pasture species mixtures to achieve reduced CH4 emissions with greater or equal livestock production.

Sheep stocking rate influences farm profit significantly; however determining the optimal stocking rate is a difficult task. In this paper, we address this challenge through three main steps. First, we review the definition of stocking rate; second, we examine prior research relevant to the review topic and highlight the factors that need to be considered when determining the optimal stocking rate; and third, we make recommendations for improvements in research on establishing the optimal sheep stocking rate. Inconsistency in the definition of stocking rate can lead to miscommunication among researchers, advisers and farmers. If 10 dry sheep equivalents (DSE)/ha is optimal for one flock, it may not be optimal for another flock because the DSE measure does not fully capture the nuances of different patterns of nutritional requirements among sheep classes and feed availabilities and their respective prices and costs. The optimal stocking rate occurs when the marginal economic benefit of an additional animal equals its marginal cost. Determining this point requires an understanding of the quantity and quality of feed available throughout the year, the optimal liveweight profile throughout the year, the impact of seasonal variation, the impact of labour availability, the cost of alternative feeds, prices of livestock and livestock products, the risk preferences of the farmer, and any emission policies relating to greenhouse gases. Farmers tend to use their own judgement to set their stocking rates, with the aim of maximising utility. However, the complexities listed make it a challenging task. Thus, researchers have used various simulation and programming models to aid decision-making over optimal stocking rates, but most farmers continue to rely on their own personal judgement. Moreover, often a focus of this modelling is for sheep systems in eastern Australia. Generalising this research across Australia is difficult due to differences in climatic conditions and markets across Australia. Often farmers are unaware of the profits they are foregoing when choosing either an overly conservative or excessive stocking rate. Our research has shown that foregone income of up to AUD50 per hectare can occur when a stocking rate 30% below or above the optimum is selected. Thus, despite the complexities that underpin the stocking rate decision, we believe that there are potential rewards from further research on the optimisation of stocking rates.

This review provides examples of the utilisation of plant bioactivity to mitigate enteric methane (CH4) emissions from the Australian ruminant production systems. Potential plant-based mitigation strategies that reduce CH4 without major impacts on forage digestibility include the following: (i) low methanogenic tropical and temperate grass, legume and shrub forage species, which offer renewable and sustainable solutions and are easy to adopt, but may have restricted geographical distribution or relatively high costs of establishment and maintenance; (ii) plant-based agricultural by-products including grape marc, olive leaves and fruit, and distiller’s grains that can mitigate CH4 and provide relatively cheap high-nutrient supplements, while offsetting the impact of agricultural waste, but their use may be limited due to unfavourable characteristics such as high protein and water content or cost of transport; (iii) plant extracts, essential oils and pure compounds that are abundant in Australian flora and offer exciting opportunities on the basis of in vitro findings, but require verification in ruminant production systems. The greatest CH4 mitigation potential based on in vitro assays come from the Australian shrubs Eremophila species, Jasminum didymium and Lotus australis (>80% CH4 reduction), tropical forages Desmanthus leptophyllus, Hetropogon contortus and Leucaena leucocephala (~40% CH4 reduction), temperate forages Biserrula pelecinus (70–90% CH4 reduction), perennial ryegrass and white clover (~20% CH4 reduction), and plant extracts or essential oils from Melaleuca ericifolia, B. pelecinus and Leptospermum petersonii (up to 80% CH4 reduction). Further research is required to confirm effectiveness of these plant-based strategies in vivo, determine optimal doses, practical modes of delivery to livestock, analyse benefit–cost ratios and develop pathways to adoption.

Greenhouse gas emissions from Western Australia's sheep flock account for 26% of the state's agricultural emissions, principally as a result of enteric methane emissions. A decrease in emissions between 2005 and 2019 can be partly explained by a 44% drop in sheep numbers over that period, but less is known about potential changes in the methane intensity of sheepmeat and wool kg CO2 equivalents/kg product. Using the livestock systems modelling software GrassGro™, we assessed the changes in methane intensity of sheepmeat and wool produced in two major sheep-producing regions in Western Australia. We also evaluated a series of future scenarios. Our results demonstrate that the observed emissions reductions are largely a result of a decrease in flock size, although methane intensity has also decreased somewhat by 11.1%. Simulation of future trajectories indicates that methane intensity could be as much as 18.8% lower by 2030, compared to 2005, with further reductions of up to 42% considered possible. The primary driver of the decreased methane intensity to date is increased flock reproductive performance through increased marking rates, higher rates of ewe lamb mating, and lower ewe death rates. However, despite reductions in methane intensity per kg of product, net emissions per ewe have risen 11.6% since 2005 and are forecast to rise by up to 21.8% by 2030, with potential further increases of up to 61% considered possible. This is driven by increased feed intake due to an increased number of lambs produced per ewe, higher ewe standard reference weights, and lower ewe death rates. Therefore, achieving absolute net reductions in the methane emissions through productivity improvements is unlikely to be prospective. Reducing net emissions is instead likely to be contingent on a reduction in flock numbers, breakthroughs in anti-methanogenic research, or via emissions offsetting. Our approach can be applied in other major livestock producing regions to evaluate emissions performance, with potential implications for agricultural and trade policy as markets increasingly seek lower emissions product.

In the rain-fed mixed-farming systems of southern Australia, the consistent supply of high-value forage is limited by a range of climatic, edaphic and systems constraints. Over 2 years, we compared biomass production and nutritional value of 30 accessions of perennial legumes, and predicted intake, grazing days and growth of ewes and lambs. There was significant variation in nutritional value and biomass production between and within species. Lucerne (Medicago sativa) and sulla (Hedysarum coronarium) produced the greatest amount of biomass and energy. There was variability among accessions in digestibility (DMD), acid detergent fibre (ADF) and crude protein, and the rate of change in these traits as plants matured. Trifolium species had the highest DMD across all growth stages. Hairy canary clover (Dorycnium hirsutum), erect canary clover (Dorycnium rectum), greater birdsfoot trefoil (Lotus uliginosus), Australian trefoil (Lotus australis) and running postman (Kennedia prostrata) had energy levels that would not maintain liveweight of mature sheep. In the second year, species differed in response to harvesting treatments. Lucerne and sainfoin (Onobrychis viciifolia) were more productive under a frequent cutting regime. Accessions of white clover (Trifolium repens), red clover (Trifolium pratense), alsike clover (Trifolium hybridum), cullen (Cullen australasicum), strawberry clover (Trifolium fragiferum), sainfoin and birdsfoot trefoil (Lotus corniculatus) showed some promise, while Tedera (Bituminaria bituminosa) and milkvetch (Astragalus cicer) performed poorly under the experimental conditions. We conclude by discussing additional agronomic and nutritional factors that need consideration when developing novel perennial legumes for mixed-farming systems in the context of a changing climate.

Ruminant livestock are raised under diverse cultural and environmental production systems around the globe. Ruminant livestock can play a critical role in food security by supplying high-quality, nutrient-dense food with little or no competition for arable land while simultaneously improving soil health through vital returns of organic matter. However, in the context of climate change and limited land resources, the role of ruminant-based systems is uncertain because of their reputed low efficiency of feed conversion (kilogram of feed required per kilogram of product) and the production of methane as a by-product of enteric fermentation. A growing human population will demand more animal protein, which will put greater pressure on the Earth’s planetary boundaries and contribute further to climate change. Therefore, livestock production globally faces the dual challenges of mitigating emissions and adapting to a changing climate. This requires research-led animal and plant breeding and feeding strategies to optimise ruminant systems. This study collated information from a global network of research farms reflecting a variety of ruminant production systems in diverse regions of the globe. Using this information, key changes in the genetic and nutritional approaches relevant to each system were drawn that, if implemented, would help shape more sustainable future ruminant livestock systems.