Dean T. Thomas

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.

Profitability of grazing crop stubbles may be overestimated by using the metabolisable energy intake from the stubble

Grazing crop stubbles affects soil structure, groundcover, and the productivity of subsequent crops, but the cost of this practice is highly variable and not easily compared against the value of feed provided to livestock. To compare with and without grazing stubbles in terms of whole-farm profit and water-use efficiency we created a mixed enterprise farm model using the Agricultural Production Systems Simulator and GRAZPLAN biophysical simulation submodels, and the Model of Integrated Dryland Agricultural System linear programming model. We hypothesised that grazing crop stubbles would increase farm profit by an amount equivalent to the value of the metabolisable energy (ME) consumed by sheep when they grazed the crop stubbles. Representative mixed farms where sheep were or were not allowed to graze crop stubbles were compared for two locations in the wheatbelt of Western Australia (Cunderdin and Geraldton) at two stocking rates. Across locations and stocking rates, the estimated value of the ME intake from crop stubbles was 2.2 times the increase in farm gross margin when stubble grazing was allowed. Contributing to this difference was that stubble grazing provided a less flexible feed source than supplementary feeding and in the absence of adjustments in stocking rates sheep tended to utilise more of the annual and permanent pastures when stubble grazing was not permitted. Therefore, the value of grazing crop stubbles to the profitability of the farm enterprise was overestimated by the ME value of the intake. Owing to reduced consumption of supplementary feed by livestock, whole-farm water-use efficiency of protein production was increased by 15% when grazing of crop stubbles was permitted. This simulation study shows that the value of grazing crop stubbles cannot be predicted well using energy intake from stubble grazing or reduced supplementary feeding costs.

Preliminary indications that Merino sheep graze different areas on cooler days in the Southern Rangelands of Western Australia

High ambient temperature can decrease weight gain in livestock, but domestic livestock in extensive grazing systems may have some capacity to adjust their behaviour to reduce the impact of periods of high temperature. We hypothesised that sheep grazing in the semiarid Southern Rangelands of Western Australia would reduce distance travelled on days with high mean daily temperature. Eight Merino ewes were fitted with GPS collars for 3 weeks in a 5575-ha paddock on Carlaminda station (28°20′S, 116°41′E). Mean daily temperature was used to separate the 18 days of the study into three temperature classes, cool (≤23.2°C), warm (23.3 to 25.9°C) and hot (≥26.0°C). Sheep travelled more quickly (P < 0.05) and further from water on cool days, compared with warm and hot days (3.74 v. 2.93 and 2.73 km from water, respectively; P < 0.001). On cool days, sheep spent most of their time grazing in the western area of the paddock. This area was rarely visited on warm or hot days. Mapping livestock distribution may assist in strategic relocation of existing water points and/or justify the development of additional watering points. However, our results suggest that sheep adjust their behaviour during hot weather, which may be a strategy to conserve energy, manage higher water requirements and/or reduce thermal load. Although grazing range decreases with higher temperatures, overall utilisation of a paddock may not be severely affected unless cooler days were too infrequent to facilitate regular access to these areas.

Increasing dietary sodium chloride increases wool growth but decreases in vivo organic matter digestibility in sheep across a range of diets

For 8 weeks, 64 Merino wethers, 18 months of age, were individually penned and offered 1 of 16 treatment feeds (n = 4). The 16 feeds were formulated to contain levels of added sodium chloride (0, 7, 14, 21%) and levels of organic matter digestibility (55, 62, 69, 76%), in a 4 × 4 factorial design. The treatment feeds were offered ad libitum for 7 weeks and at maintenance for the final week. Clean wool growth, corrected for digestible organic matter intake, increased by 16, 18 and 27% as added sodium chloride was increased (7, 14, and 21%). The increase in wool growth was similar for diets at all levels of formulated organic matter digestibility. Feed digestibility in sheep decreased when added dietary sodium chloride was 14% or higher. The decrease in organic matter digestibility was ∼5 percentage units at the highest level (21%) of dietary sodium chloride. Liveweight gain in sheep was reduced from 143 to 134, 65 and 1 g/day with 7, 14 and 21% added dietary sodium chloride, respectively. Therefore, improvement in wool growth efficiency appears to occur at the expense of liveweight gain, and was probably related to a shift in digestion of feed from the stomach to the small intestine. Higher corrected clean wool growth associated with lower levels of purine derivatives (an indicator of microbial protein synthesis) supported the conclusion that increased dietary salt resulted in an increase in dietary protein being digested in the small intestine. A shift in feed utilisation towards increased wool growth as dietary salt increases may be a management tool of particular interest to specialist wool producers. In areas of saline land where salt-accumulating shrubs are often the most productive vegetation, an increase in wool production efficiency, even if liveweight is only maintained, may improve the profitability of incorporating these shrubs into a feeding strategy.

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.

Australian and Spanish scientists are collaborating in the domestication of tedera: young Merino sheep grazing a monoculture of tedera in autumn showed preference for certain accessions but no signs of ill health

Abstract. We hypothesised (i) that sheep grazing a monoculture of tedera (Bituminaria bituminosa (L.) C.H. Stirton var. albomarginata and var. crassiuscula) would not show signs of photosensitisation or ill health, and (ii) that when given free grazing choice they would show a repeatable preference for certain accessions of tedera related to their chemical composition. We tested this by grazing a group of young merino wethers on a monoculture containing seven accessions of tedera for 21 days. General health was assessed via daily visual checks for skin pinkness on the nose and ears, weekly measures of liveweight, condition score, and blood analysis compared with a group of control sheep fed wheaten hay ad libitum. The Chesson–Manly selection index was used to examine the relative preference of sheep for the seven accessions of tedera over the 21 days. Each accession of tedera was sampled weekly to estimate the dry matter on offer, and these samples were also analysed for crude protein, neutral detergent fibre, acid detergent fibre, in vitro digestibility, water soluble carbohydrates, minerals, and concentrations of the furanocoumarins psoralen and angelicin. None of the sheep showed any signs of ill health, with all blood parameters being within the normal reference range. All sheep gained weight and body condition over the 21 days. The difference in the rate of gain in condition score in favour of the sheep grazing tedera over the 21 days (0.014 v. 0.002 unit/sheep.day) was significant (P < 0.001). Sheep showed repeated preference for accessions T31 and T43 (α >0.143). Nutritive value of all accessions of tedera was high. However, only acid detergent fibre and neutral detergent fibre affected the relative preference of the sheep (P < 0.05) and they were only weakly correlated (r2 = 0.208 and 0.165, respectively). We conclude that there are accessions of tedera that are preferred by sheep that could be used to fill the autumn feed gap experienced in the south of Western Australia without any risk to the health of the sheep.

Selection of crop cultivars suited to the location combined with astute management can reduce crop yield penalties in pasture cropping systems

Abstract. Pasture cropping is an emerging farming-systems practice of southern Australia, in which winter grain crops are sown into an established stand of a winter-dormant, summer-growing perennial pasture. There is a pressing need to define times, locations and climates that are suitable for pasture cropping. To evaluate effects of management interventions, agro-environment, and possible interactions on crop and pasture productivity associated with pasture cropping, an AusFarm® simulation model was built to describe a pasture-cropping system based on annual crop and subtropical grass. The model was parameterised using data from field research on pasture cropping with barley cv. Buloke and a C4 subtropical grass, Gatton panic (Panicum maximum cv. Gatton), conducted at Moora, Western Australia. The simulation was run over 50 years using the historical climate data of five southern Australian locations (Cunderdin, Jerdacuttup, Mingenew, and Moora in Western Australia, and Karoonda in South Australia). Two wheat cultivars and one barley crop were considered for each location, to examine the impact of crop phenology on this farming system. Jerdacuttup and Moora favoured pasture cropping, with average barley-yield penalties of 10 and 12%. These locations were characterised by colder growing seasons, more plant-available water at anthesis, and more winter–spring rain. The cereal crops did not rely on stored soil moisture, growing instead on incident rain. The winter–spring growth of the Gatton panic pasture was highest at Mingenew. This generated a high yield penalty, 38% loss under pasture cropping, compared with the other locations. Changing the efficacy of a herbicide application to the pasture when the crop was sown had a strong effect on yield. Yield penalties at Moora and Mingenew reduced to 7 and 29%, respectively, when the proportion of live biomass killed by the herbicide was doubled. Utilisation of soil moisture by the Gatton panic pasture during summer and early autumn had little effect on subsequent grain yield, whereas reduced pasture growth during the winter–spring growing period had a substantial effect on crop yield. Pasture cropping can therefore succeed in agro-climatic regions where crops can be grown on incident rain and pasture growth is suppressed through low temperature or herbicide. Perennial pasture growth should be minimised during the crop growing period through the management of crop sowing date, nitrogen fertiliser application and C4 grass suppression to minimise the effect on stored soil water at crop anthesis.

Whole Farm Net Greenhouse Gas Abatement from Establishing Kikuyu-Based Perennial Pastures in South-Western Australia

Simple Summary Greenhouse gas (GHG) emissions from ruminant livestock production (sheep, cattle and goats) have contributed to a common perception that a shift in the human diet from animal to plant-based products is environmentally responsible. In this study we found that the level of net emissions from livestock production systems is strongly influenced by the type of farming system that is used, and in fact GHG emission levels from some livestock production systems may be comparable with cropping systems. By introducing into farming systems ‘perennial’ pasture plants that are able to capture more atmospheric carbon, which is then stored in the soil, emission levels from livestock production can be substantially reduced. Abstract On-farm activities that reduce GHG emissions or sequester carbon from the atmosphere to compensate for anthropogenic emissions are currently being evaluated by the Australian Government as carbon offset opportunities. The aim of this study was to examine the implications of establishing and grazing Kikuyu pastures, integrated as part of a mixed Merino sheep and cropping system, as a carbon offset mechanism. For the assessment of changes in net greenhouse gas emissions, results from a combination of whole farm economic and livestock models were used (MIDAS and GrassGro). Net GHG emissions were determined by deducting increased emissions from introducing this practice change (increased methane and nitrous oxide emissions due to higher stocking rates) from the soil carbon sequestered from growing the Kikuyu pasture. Our results indicate that livestock systems using perennial pastures may have substantially lower net GHG emissions, and reduced GHG intensity of production, compared with annual plant-based production systems. Soil carbon accumulation by converting 45% of arable land within a farm enterprise to Kikuyu-based pasture was determined to be 0.80 t CO2-e farm ha−1 yr−1 and increased GHG emissions (leakage) was 0.19 t CO2-e farm ha−1 yr−1. The net benefit of this practice change was 0.61 t CO2-e farm ha−1 yr−1 while the rate of soil carbon accumulation remains constant. The use of perennial pastures improved the efficiency of animal production almost eight fold when expressed as carbon dioxide equivalent emissions per unit of animal product. The strategy of using perennial pasture to improve production levels and store additional carbon in the soil demonstrates how livestock should be considered in farming systems as both sources and sinks for GHG abatement.

An on-farm evaluation of the capability of saline land for livestock production in southern Australia

Grazing livestock on revegetated saline land is one of few profitable options to continue using this class of agricultural land. However, there has been little research conducted to assess the capability of saline land to support livestock production based on the soil and water characteristics at a particular site. In this study, data from 11 grazing studies collected from eight commercial farms across southern Australia were used to estimate metabolisable energy (ME) utilised/ha, as well as total ME produced/ha. All data were from the autumn (March–May) period, when feed is normally in short supply and of limited quality. Site characteristics indicative of the severity of salinisation varied across the sites. Topsoil electrical conductivity (ECe) ranged from 1 to 33 dS/m and groundwater EC from 14 to 60 dS/m (equivalent to sea water). Feed on offer before grazing varied from 700 kg dry matter/ha to 9000 kg dry matter/ha between sites. Thinopyrum ponticum and Puccinellia ciliata featured prominently in the less saline revegetated sites, with Atriplex spp. present on the more saline sites and some lucerne and rhodes grass on the less saline, well drained sites. Grazing days per ha for sheep (ME-adjusted dry sheep equivalent) on autumn pastures across the sites ranged from 41 to 3600, and liveweight gains ranged from –95 to 314 g/sheep.day. The grazing value of the highest producing saltland was at least as high as that expected on adjacent areas that were not salt affected. The major advantage of establishing saltland pastures included an out-of-season feed supply high in crude protein and micronutrients that possessed the ability to capture summer and autumn rain. This should represent a substantial reduction in supplementary feed costs and increases the flexibility of methods for feeding livestock through periods of low annual pasture availability. The value of the ME produced on the highest yielding saltland pasture was estimated to be

Grazing winter and spring wheat crops improves the profitability of prime lamb production in mixed farming systems of Western Australia

360/ha based on substituting the best alternative strategy of purchasing lupin grain as a supplement. A quadratic relationship (R2 = 0.62, P = 0.024) was found between soil ECe and ME produced across the sites. Significant relationships were not found between other saline site characteristics and ME production, which partly reflects the complexity of these systems as well as limitations with site characterisation.