Clinton Revell

Temperate pasture legumes in Australia—their history, current use, and future prospects

Abstract. Australian farmers and scientists have embraced the use of new pasture legume species more than those in any other country, with 36 annual and 11 perennial legumes having cultivars registered for use. Lucerne (Medicago sativa), white clover (Trifolium repens), and red clover (T. pratense) were introduced by the early European settlers and are still important species in Australia, but several other species, notably annual legumes, have been developed specifically for Australian environments, leading to the evolution of unique farming systems. Subterranean clover (T. subterraneum) and annual medics (Medicago spp.) have been the most successful species, while a suite of new annual legumes, including serradellas (Ornithopus compressus and O. sativus), biserrula (Biserrula pelecinus) and other Trifolium and Medicago species, has expanded the range of legume options. Strawberry clover (T. fragiferum) was the first non-traditional, perennial legume commercialised in Australia. Other new perennial legumes have recently been developed to overcome the soil acidity and waterlogging productivity constraints of lucerne and white clover and to reduce groundwater recharge and the spread of dryland salinity. These include birdsfoot trefoil (Lotus corniculatus), Talish clover (T. tumens), and hairy canary clover (Dorycnium hirsutum). Stoloniferous red clover cultivars and sulla (Hedysarum coronarium) cultivars adapted to southern Australia have also been released, along with a new cultivar of Caucasian clover (T. ambiguum) aimed at overcoming seed production issues of cultivars released in the 1970s. New species under development include the annual legume messina (Melilotus siculus) and the perennial legume narrowleaf lotus (L. tenuis) for saline, waterlogged soils, and the drought-tolerant perennial legume tedera (Bituminaria bituminosa var. albomarginata). Traits required in future pasture legumes include greater resilience to declining rainfall and more variable seasons, higher tolerance of soil acidity, higher phosphorous utilisation efficiency, lower potential to produce methane emissions in grazing ruminants, better integration into weed management strategies on mixed farms, and resistance to new pest and disease threats. Future opportunities include supplying new fodder markets and potential pharmaceutical and health uses for humans and livestock. New species could be considered in the future to overcome constraints of existing species, but their commercial success will depend upon perceived need, size of the seed market, ease of establishment, and management and safety of grazing animals and the environment. Molecular biology has a range of potential applications in pasture legume breeding, including marker-assisted and genomics-assisted selection and the identification of quantitative trait loci and candidate genes for important traits. Genetically modified pasture plants are unlikely to be commercialised until public concerns are allayed. Private seed companies are likely to play an increasingly important role in pasture legume development, particularly of mainstream species, but the higher risk and more innovative breakthroughs are likely to come from the public sector, provided the skills base for plant breeding and associated disciplines is maintained.

Preference of sheep among annual legumes is more closely related to plant nutritive characteristics as plants mature.

We hypothesised that the preference of sheep among a wide range of annual legumes at successive stages of plant phenology would be related to laboratory measurements of the chemical composition of the forage. We tested this by examining the relative preferences of sheep among 20 genotypes of annual plants at three phenological stages of plant growth usingtheChesson-Manlyselectionindex.Plantmaterialwascollected forlaboratoryanalysesateachphenological stage and samples were analysed for nitrogen, sulfur, neutral detergent fibre, acid detergent fibre, in vitro digestibility and water soluble carbohydrates. Sheep differed in relative preference among the plant genotypes within and between each of the three phenological stages. Vegetative characteristics that were correlated with relative preference also differed with plant phenology. Measured characteristics of the plant material explained an increasing proportion of the variance in relative preference with successive phenological stages (4.8, 51.1 and 60.9% at the vegetative, reproductive and senesced stages; P < 0.001). The relative preference of the sheep depended on the overall quality of the vegetation. When the quality of the vegetation was high, relative preference did not correlate well with measured nutritive characteristics. However, whenthevegetationwasoflowquality,sheepselectedplantswithcharacteristicsassociatedwithhighernutritivevalue.We conclude that sheep adopt different foraging strategies in response to changing vegetation characteristics and increase their preference for plants that increase their intake of digestible dry matter as the sward matures.

The relative feeding value of a new pasture legume, eastern star clover (Trifolium dasyurum), compared with subterranean clover (Trifolium subterraneum)

An accession of eastern star clover (Trifolium dasyurum C. Presl.), a new species to agriculture, has been identified by the National Annual Pasture Legume Improvement Program for commercial release in Australia. This paper reports the findings of an experiment designed to assess the feeding value of eastern star clover compared with a commercial cultivar of subterranean clover (T. subterraneum L. cv. Dalkeith). The hypothesis tested in this experiment is that sheep grazing eastern star clover will have similar growth rates, condition scores, and wool production to sheep grazing subterranean clover. Additionally, it is hypothesised that the sheep grazing the different clover species will have similar health and meat quality. The relative feeding value of the 2 clover species was tested using 14-month-old Merino wethers, grazing 8 by 0.5 ha plots (4 of each species). Stocking rates were such that herbage mass availability would not have limited feed intake. Liveweight, wool growth, and animal health were monitored. After 10 weeks of grazing, 2 animals from each plot were slaughtered for sensory analysis of meat. Although there were generally no differences in liveweight change, condition, or wool growth between sheep grazing eastern star or subterranean clovers, sheep in the subterranean clover plots grew faster during the first month of grazing. There were no differences in meat eating quality (tenderness, juiciness, or flavour), animal health, or vegetable matter contamination of wool. The data suggest that the clovers had the same relative feeding value despite herbage mass from the eastern star clover plots having lower in vitro digestibility, crude protein, and higher fibre than herbage mass from the subterranean clover plots. Given that there was a minimum of 1000 kg/ha of herbage mass in the plots, it is likely that sheep gazing the two clovers were able to maintain the same weight by selecting the high quality components of the pasture. Differences in plant quality are associated with differences in reproductive strategies of the clovers.

Breeding and farming system opportunities for pasture legumes facing increasing climate variability in the south-west of Western Australia

Abstract. The south-west of Western Australia has experienced a declining trend in annual rainfall and gradual warming over the last 30 years. The distribution of rainfall has also changed, with lower autumn rainfall, patchy breaks to the season, and shorter springs. This has important implications for the productivity of legume pastures in the region, which is dominated by annual species, particularly subterranean clover (Trifolium subterraneum L.), annual medics (Medicago spp.), serradella (Ornithopus spp.), and biserrula (Biserrula pelecinus L.). For annual pasture legumes, appropriate patterns of seed softening and germination behaviour, efficiency of phosphorus and potassium uptake, responses to elevated levels of atmospheric CO2, and drought resistance of seedlings and mature plants will assume increasing importance. While these traits can be targeted in pasture breeding programs, it will also be important to exploit farming system opportunities to optimise the annual legume component of the feed base. These opportunities may take the form of incorporating strategic shrub reserves and grazing crops to allow for pasture deferment in autumn–winter. Perennial forages may become more important in this context, as discussed in terms of the development of the perennial legume tedera (Bituminaria bituminosa var. albomarginata C.H. Stirton).

Effects of Prima gland clover (Trifolium glanduliferum Boiss cv. Prima) consumption on sheep production and meat quality

Gland clover (Trifolium glanduliferum Boiss) is a recently introduced and released clover species for use in Mediterranean agricultural systems in southern Australia. There is little information on the expected animal production from this pasture plant although it is known to contain coumarins. Coumarins may have a direct effect on the production of grazing ruminants through a reduction in feed intake and may also have the ability to influence the flavour and odour of meat. In this study, Merino hogget ewes were grazed on eight 0.5 ha replicate plots sown to monocultures of either Prima gland clover or Dalkeith subterranean clover (Trifolium subterraneum ssp. subterraneum L.). The Prima gland clover was estimated to contain between 80 and 300 mg coumarin/kg dry matter. Three sheep were allocated to the plots on 7 September and 1 sheep from each plot was slaughtered on 29 September. Two additional sheep were allocated to the plots on 28 September and another 2 on 19 October. At the end of the experiment on 8 November, each plot contained 2 sheep that had grazed for 3, 6 or 9 weeks. All sheep were slaughtered at this time. The 2 sheep that remained on the plots from 7 September to 8 November were used for the comparison of animal production between the 2 clover species. Following slaughter, measurements were made of carcass characteristics and meat eating quality. The liveweight gain and wool growth of the 2 treatments were similar over the 9 weeks, however, the sheep on the Prima gland clover plots grew faster over the first 3 weeks. The faster growth rate is consistent with a higher in vitro digestibility of the Prima gland clover at this time. The similarity in feeding value of the 2 clover species indicates that there was no depression in feed intake associated with the Prima gland clover. There were some small significant differences in meat eating quality between the groups. Meat from sheep grazing the Prima gland clover was drier and had a more pleasant taste. These differences are unlikely to be large enough to have any commercial significance. The results indicate that the Prima gland clover has a feeding value at least equivalent to the Dalkeith subterranean clover and that, under the conditions of this experiment, the coumarin concentrations in the Prima gland clover are not high enough to affect either feed intake or the flavour and odour of meat.

Evaluation and breeding of tedera for Mediterranean climates in southern Australia

Abstract. Tedera (Bituminaria bituminosa C.H. Stirton var. albomarginata and var. crassiuscula) has been identified as one of the most productive and drought-tolerant species of herbaceous perennial legumes based on 6 years of field evaluation in Western Australia in areas with Mediterranean climate and annual rainfall ranging from 200 to 600 mm. Importantly, tedera demonstrated broad adaptation to diverse soils, and some accessions have shown moderate levels of tolerance to waterlogging and salinity. Tedera exhibits minimal leaf shedding during summer and autumn. Economic modelling strongly suggests that giving livestock access to green tedera in summer and autumn will dramatically increase farm profit by reducing supplementary feeding. The breeding program (2006–12) evaluated the available genetic diversity of tedera for its field performance in seven nurseries with 6498 spaced plants in total covering a wide variation in rainfall, soils and seasons. Best overall plants were selected using a multivariate selection index generated with best linear unbiased predictors (BLUPs) of dry matter cuts and leaf retention traits. The breeding program also evaluated tedera for grazing tolerance, grazing preference by livestock, waterlogging tolerance, seed production, cold tolerance, disease susceptibility and presence of secondary compounds. Tedera is a diploid, self-pollinated species. Therefore, 28 elite parents were hand-crossed in several combinations to combine outstanding attributes of parents; F1 hybrids were confirmed with the aid of highly polymorphic, simple sequence repeat markers. The F1s were progressed to F4s by single-seed descent breeding. Elite parent plants were selfed for two generations to be progressed in the breeding program without hybridisation. Over time, selections from the crossing and selfing program will deliver cultivars of three ideotypes: (i) drought-tolerant, (ii) cold- and drought-tolerant, (iii) waterlogging- and drought-tolerant.

Biserrula pelecinus L. – genetic diversity in a promising pasture legume for the future

Abstract. Biserrula pelecinus L. is a Mediterranean annual pasture legume and performs best on well drained sandy loams and medium loams with a pH 4.5–7. It is not suited to areas prone to waterlogging but persists well, even with hard summer grazing and in rotational systems. It is deep-rooted and remains green long after traditional pastures have dried off. Diversity analysis of germplasm collection of 279 accessions using 18 agro-morphological traits, 22 eco-geographical specifications of the collection sites, and amplified fragment length polymorphisms markers was conducted to develop a core collection of ∼10% of the original collection. This core collection of 30 accessions from seven countries well represented the diversity of the whole collection. This core will be exploited for variation in photosensitivity effect in sheep together with other economically important traits challenging the livestock industry.

Mauro: a mid to late maturing cultivar of biserrula (Biserrula pelecinus)

Mauro is a new mid to late variety of biserrula. It was derived from a single plant selection from a population collected from a harsh and heavily grazed site in southern Sardinia, Italy. The later maturity, lower hard seed level and higher regeneration in the second year of Mauro compared with Casbah will enhance the performance of biserrula in areas with medium to high rainfall where permanent pasture or infrequent cropping are common.

Small effects of deferment of annual pastures through grazing spring wheat crops in Western Australia can benefit livestock productivity

Abstract. Grazing sheep on cereal crops in winter has become widely adopted in medium–high-rainfall zones of Australia. Interest in this practice has spread to the lower rainfall parts of the cereal–livestock zone where it is being applied to shorter season crop varieties. A farm-system modelling study was conducted to investigate the value of deferment of annual pastures by grazing spring wheat in their place. The biophysical simulation model, based on a representative wheat and sheep farming system in the wheatbelt of Western Australia, involved two grazing-management scenarios and used climate data for the period 1962–2011 for three locations in Western Australia representing low-, medium- and high-rainfall cropping regions: Merredin, Wickepin and Kojonup. The grazing-management policy of the main scenario, ‘crop grazing’, placed livestock on the crops only until the crop reached Zadoks growth stage 30, provided the green biomass of the farm’s annual pastures was <800 kg/ha. A second ‘shadow-grazing’ scenario was run in which a group of ewes identical to the main ewe flock was used to graze annual pastures simultaneously with the main ewe flock whenever the main flock grazed wheat crops. The difference between the two scenarios represented the pasture deferment value associated with grazing wheat crops. Pasture deferment had little effect on total pasture production during the period when crops were grazed. However, there was a small benefit to feed supply through the accumulation of pasture during the period of crop grazing. This feed was available at a time of year when feed is scarce. This was reflected in improved animal production, with the weight of lambs at weaning being higher in the crop-grazing scenario than the shadow-grazing scenario. These results suggest that although increases in pasture productivity and feed supply associated with spring crop grazing are only marginal, grazing of spring wheat crops can still lead to changes in lamb production because this enterprise is sensitive to the feed supply in winter.

In vitro ruminal fermentation characteristics and methane production differ in selected key pasture species in Australia

Abstract. Thirteen current and potential pasture species in southern Australia were examined for differences in their nutritive values and in vitro rumen fermentation profiles, including methane production by rumen microbes, to assist in selection of pasture species for mitigation of methane emission from ruminant livestock. Plants were grown in a glasshouse and harvested at 7 and 11 weeks after sowing for in vitro batch fermentation, with nutritive values assessed at 11 weeks of growth. The pasture species tested differed significantly (P < 0.001) in methane production during in vitro rumen fermentation, with the lowest methane-producing species, Biserrula pelecinus L., producing 90% less methane (4 mL CH4 g–1 dry matter incubated) than the highest methane-producing species, Trifolium spumosum L. (51 mL CH4 g–1 dry matter incubated). Proxy nutritive values of species were found not to be useful predictors of plant fermentation characteristics or methane production. In conclusion, there were significant differences in fermentative traits, including methane production, among selected pasture species in Australia, indicating that the choice of fodder species may offer a way to reduce the impact on the environment from enteric fermentation.