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Dual-purpose use of canola ( Brassica napus ) for forage in winter before seed production is a practice recently developed in southern Australia. The feasibility for dual-purpose spring canola ( B. napus annua ) in the medium-rainfall zone (450–650 mm) has been demonstrated commercially, with significant adoption. Testing of later-maturing, dual-purpose winter canola ( B. napus biennis ) in long-season, high-rainfall areas (>650 mm) has been restricted to mechanical defoliation or crash grazing. We conducted a series of six field experiments to evaluate the crop and livestock productivity of dual-purpose winter canola, involving a variety of stocking rates, grazing regimens and different cultivars at Canberra, ACT, and Young, NSW, in south-eastern Australia in 2007 and 2008. European winter canola cultivars sown between 21 March and 21 April provided 800–1100 dry sheep equivalent (DSE) grazing days/ha in Canberra and 1550–2600 DSE grazing days/ha in Young with little impact on subsequent yield (range 2.6–5.8 t/ha), provided the sheep were removed from crops prior to bud elongation. Grazing occurred between 18 June and 1 September in Canberra and between 16 June and 14 August in Young and generally had no effect on harvest index or oil content. High stocking rates for short duration (126 DSE/ha for 7 days) reduced sheep live-weight gains and meat production by ∼50% (110 g/day; 92 kg/ha) compared with stocking rates of low (22 DSE/ha for 47 days) or moderate (43 DSE/ha for 22 days) stocking rates (mean 220 g/day; 182 kg/ha) despite similar overall grazing pressure (882–1034 DSE grazing days/ha). The flexibility in sowing date and grazing times afforded by the vernalisation characteristics of winter canola make it an ideal, flexible option in high-rainfall mixed-farming systems. Winter canola could complement or even replace the traditional later-sown spring cultivars (for dual-purpose and/or grain-only production) in areas with high rainfall (>650 mm) where early sowing opportunities (March) and cooler spring temperatures can maximise yield. Our results demonstrate significant potential for high livestock production and high grain and oil yield from dual-purpose winter canola in high-rainfall environments.

The utilisation of dual-purpose crops, especially wheat and canola grown for forage and grain production in sheep-grazing systems, is reviewed. When sown early and grazed in winter before stem elongation, later-maturing wheat and canola crops can be grazed with little impact on grain yield. Recent research has sought to develop crop- and grazing-management strategies for dual-purpose crops. Aspects examined have been grazing effects on crop growth, recovery and yield development along with an understanding of the grazing value of the crop fodder, its implications for animal nutrition and grazing management to maximise live-weight gain. By alleviating the winter 'feed gap', the increase in winter stocking rate afforded by grazing crops allows crop and livestock production to be increased simultaneously on the same farm. Integration of dual-purpose wheat with canola on mixed farms provides further systems advantages related to widened operational windows, weed and disease control and risk management. Dual-purpose crops are an innovation that has potential to assist in addressing the global food-security challenge.

Attempting to achieve a balance between the supply of and requirements for the major nutrients implies that demands for major nutrients can be adequately quantified, that the nutritive value of the consumed diet can be described in similar terms and that the diet actually consumed by the grazing sheep can be estimated, or at least predicted, from pasture and animal conditions. Several systems exist for defining the nutrient requirements of sheep and, whilst there are real differences between them, all are sufficiently accurate to allow their use in ration formulation and in grazing animal management. Similarly, nutritive value of feed components can be defined accurately. In grazing sheep, the major difficulty in balancing the supply of consumed nutrients against nutrient requirements is the estimation of diet composition and intake. Computer-based decision support tools are a useful aid to overcoming this problem. It is suggested that since profit derives from animal production per hectare and not per animal, the balancing of nutrient supply and requirements should not be attempted on an individual-animal basis.

Plant-wax markers can be used for estimating forage intake, diet composition and supplement intake in grazing livestock, wild ruminants and other mammals. We describe protocols for using the saturated hydrocarbons (alkanes) of plant wax as markers for estimating fecal output, intake and digestibility. Procedures for investigating digestion kinetics are also discussed. Alkanes can also be used to estimate diet composition and the procedures required to do this are also described, including the special case where supplementary feed is treated as a component of the diet composition estimate. The long-chain alcohols (LCOHs) and very long-chain fatty acids (VLCFAs) of plant wax show particular promise for discriminating a greater number of species in the diet. The use of all these plant-wax markers in nutrition studies depends on having quantitative, repeatable and mutually compatible assay procedures for alkanes, LCOHs and VLCFAs; we present protocols for these assays in detail. Analysis of a single sample of feces or plant material for all these plant-wax markers can be completed within 2 days; however, it is possible to process up to 50 samples (analyzed in duplicate) per week.

The use of plant-wax markers for estimating forage intake, diet composition and supplement intake in grazing/browsing sheep and goats is reviewed in relation to some of the shortcomings of pre-existing techniques. The saturated hydrocarbons (alkanes) of plant wax are well validated as markers for estimating intake. Alkane-based estimates of intake have the advantage of accommodating individual differences in digestibility and those arising from supplement/forage interactions. Alkanes can also provide an estimate of diet composition and hence the inputs required to estimate herbage intake. Total intake can thus be partitioned into intake of individual species. It is probable that the alkane approach to estimating diet composition can discriminate fewer species in the diet of sheep and especially goats, than these animals encounter in complex plant communities. We discuss approaches to coping with this issue, such as grouping species in diet composition estimates, and the use of other plant-wax markers as diet composition markers. The long-chain alcohols and fatty acids are shown to have particular promise for discriminating a greater number of species in the diet. We then discuss the estimation of supplement intake using plant hydrocarbons, as a special case of the estimation of diet composition. Finally, we demonstrate that when supplement intakes are known, alkane-based estimates of the supplement proportion in the diet can be used to estimate the intake of all dietary components, without the need to dose animals with synthetic alkanes.

This paper reports results from a study of ewes in pregnancy and lactation, during which times they grazed at a high versus medium stocking rate and either received or did not receive a pelleted supplement. We measured ewe liveweight, condition score and body composition; intakes by ewes of pasture and supplementary feed; milk production by ewes, and; birthweight, milk intake, liveweight gain and body composition of single and twin lambs. Ewes grazing at the medium stocking rate consumed more pasture in late pregnancy and the intake of supplement significantly reduced pasture intake. Nevertheless, total intakes of organic matter or digestible organic matter were unaffected by supplementation and were significantly higher at the medium stocking rate. Effects of stocking rate on intake persisted into early and mid-lactation, but supplement intake did not affect pasture intake in lactation. Pasture intakes in pregnancy were not markedly different between twin-bearing and single-bearing ewes, nor were pasture intakes in lactation affected by the number of lambs suckled. Ewes suckling twins produced much more milk. There were significant effects of birth type, ewe stocking rate and supplementation on lamb milk intake and liveweight gain. The data were reanalysed by regression, to explore the effects of actual herbage masses and ewe intakes, and the possible effects of non-treatment terms such as ewe age, condition score and dentition score at allocation. These analyses confirmed the above effects of treatment, but also demonstrated that ewes in better condition at the start of the experiment ate less pasture in both pregnancy and lactation, and produced significantly less milk. Ewe organic matter intakes in pregnancy were not related to dentition score at allocation, but in early and mid-lactation were reduced by ~170 g organic matter/day and 280–380 g organic matter/day, respectively, per unit increase in dentition score. There was no significant effect of ewe dentition score on lamb milk intake, but there was a significant penalty of ~19 g lamb liveweight gain/unit increase in ewe dentition score at allocation. Future studies of this kind thus need to include estimates of the condition score and dentition score of ewes when they commence the experiment.

CSIRO Plant Industry has developed the GRAZPLAN family of decision support tools (DS tools) for consultants and farmers to improve the profitability and environmental sustainability of grazing enterprises. These tools are based on pasture and animal production models that have general application for simulating the biophysical processes of grazing systems in temperate southern Australia. The DS tools are designed to be easy to use and, apart from daily weather information, require minimal input of data. Where relevant, the models run continuously over a range of specified years, without further intervention by the user. The output generated can be linked to cost and price indices to enable estimation of production risk in financial as well as in biological terms. Adoption of GrazFeed, a tool to guide livestock nutrition, is widespread in the southern states where it is a keystone for the very successful PROGRAZE extension program sponsored by NSW Agriculture and Meat and Livestock Australia. GrazFeed's success is linked to the release of national feeding standards for ruminants, to the tactical nature of decisions about livestock nutrition and to a formal commitment by CSIRO, the developers, with NSW Agriculture, a major user. Adoption of another tool, GrassGro, which is used to analyse grazing enterprises for profit and sustainability, is slower. In this case the decision support is concerned with strategic planning where outcomes are probability-based and where the pasture model in GrassGro is not based on an agreed national standard. Confidence in the use of GrassGro increases where users are already familiar with GrazFeed, which contains an identical animal model. A key component of the commercial release of GrassGro is the provision of an intensive training course. Future adoption of the DS tools will be enhanced by their innovative use in teaching programs such as that at the University of New England where they are used in all undergraduate years of the rural science course.

The utilisation of dual-purpose crops, especially wheat and canola grown for forage and grain production in sheep-grazing systems, is reviewed. When sown early and grazed in winter before stem elongation, later-maturing wheat and canola crops can be grazed with little impact on grain yield. Recent research has sought to develop crop- and grazing-management strategies for dual-purpose crops. Aspects examined have been grazing effects on crop growth, recovery and yield development along with an understanding of the grazing value of the crop fodder, its implications for animal nutrition and grazing management to maximise live-weight gain. By alleviating the winter 'feed gap', the increase in winter stocking rate afforded by grazing crops allows crop and livestock production to be increased simultaneously on the same farm. Integration of dual-purpose wheat with canola on mixed farms provides further systems advantages related to widened operational windows, weed and disease control and risk management. Dual-purpose crops are an innovation that has potential to assist in addressing the global food-security challenge.

Grazing of cereal crops reduces canopy light interception and could potentially reduce biomass production and grain yields. Alternatively, defoliation after canopy closure may increase light penetration and enhance radiation-use efficiency (RUE, shoot dry matter produced per unit light intercepted). Changes in dry matter partitioning following grazing may also ameliorate grain yield penalties. Experiments with rainfed winter wheat were conducted near Canberra, Australia, to investigate the effect of different intensity or duration of grazing on two cultivars. Grazing reduced leaf area index (LAI), light interception and growth rates by up to 90% but did not affect overall RUE. Although grazing caused significant reductions in cumulative light interception and total dry matter accumulation, it did not affect grain yields because grazed crops had delayed phenological development, allowing increased partitioning of shoot dry matter to spikes. Grazing reduced stem dry matter accumulation and consequently decreased the amount of stem assimilate available for retranslocation to kernels by up to 75%. However, by delaying crop ontogeny, grazing prolonged green area duration after anthesis and thereby increased the supply of assimilates from current photosynthesis to developing kernels, mitigating potential yield penalties caused by defoliation.

Detailed information on the growth dynamics, yield responses and soil water use of dual-purpose cereal crops after grazing is often required to devise guidelines for profitable grazing management. To increase the availability of such data, grazing experiments with winter wheat (Triticum aestivum) were conducted near Canberra, Australia. In 2007, cultivar Mackellar was grazed at low-short (LS, 33 sheep/ha for 31 days), heavy-short (HS, 67 sheep/ha for 31 days) or low-long (LL, 33 sheep/ha for 62 days) intensity-durations. In 2008, cultivars Mackellar and Naparoo were grazed at the HS intensity-duration. Aboveground net primary production (ANPP) of ungrazed Mackellar crops averaged 1181 g/m2. LS and HS grazing did not affect ANPP in 2007, but LL grazing in 2007 and HS grazing in 2008 treatments reduced ANPP by 20% (which included biomass removed by livestock). Average grain yield (381 g/m2) was not significantly affected by grazing. Grazing increased the proportion of water lost through soil evaporation but decreased transpiration, reducing shoot dry matter production per unit evapotranspiration by up to 22%. However, grazing did not affect grain yield per unit evapotranspiration. For rainfed wheat crops grown in temperate environments, greater biomass production occurred with shorter rather than longer grazing durations, irrespective of grazing intensities.

The nutrient intakes of mammalian herbivores depend on the amount and the nutrient content of the plant species and plant parts which they eat. We review the merits of oesophageal-fistulated (OF) animals, microhistological procedures, stable C-isotope discrimination and plant cuticular-wax markers as methods for estimating diet composition and intake in both ruminant and non-ruminant herbivores. We also briefly discuss methods based on grazing behaviour measurements or on H2O or Na turnover, and methods for estimating supplement or soil intake. Estimates of intake in ruminants are often based on separate measurements of faecal output and herbage digestibility. We review this approach and emphasize that, under some circumstances, the applicability ofin vitrodigestibility estimates based on OF extrusa is questionable. We discuss how plant-wax marker patterns can be used to check whether OF and test animals are consuming similar diets, but also emphasize that a major advantage of the use of plant-wax markers is that this approach may obviate altogether the need for OF animals. Estimates of total herbage intake can be partitioned into the intakes coming from different plant species and/or parts, provided diet composition can be measured. Diet composition estimates based on C-isotope discrimination have the major disadvantage that they cannot be taken to species level. By contrast, microhistological methods can identify many plant species in extrusa, digesta or faeces, but often a large proportion of plant fragments remains unidentifiable. Plant-wax hydrocarbons show great promise as markers for estimating diet composition and intake. However, we suggest that to be applicable in complex plant communities there is a need with this method either to recruit a wider range of wax markers (e.g. alcohols, sterols, fatty acids) or to use it in combination with other methods. We suggest that, in turn, this generates an urgent need for research on statistical aspects of the combined use of markers or methods, in relation to the error structures of the data or methods being combined and the standard errors of the resultant estimates of diet composition and intake. We conclude by discussing the extension of intake and/or diet composition measurements to the measurement of nutrient transactions within the gut, particularly in relation to the supply of absorbable nutrients.

The grazing of cereal and canola crops during winter is an increasing component of grazing systems in southern Australia. The capacity of such crops to meet the requirements of young livestock and reproducing animals for sodium (Na), magnesium (Mg), calcium (Ca) and potassium (K) is reviewed. The growth responses of young stock to Na and/or Mg supplements when grazing wheat are discussed. These responses differ from ‘literature expectation' in that they are rapid in onset and involve no clinical signs. We demonstrate that more insight about the variability in supplement response, both between and between crops species, is obtained when mineral contents are viewed from the perspective of their frequency distributions, rather than their mean values. The pivotal importance of high K concentration, low Na and the resultant K:Na ratio of forage is stressed, as is the interaction of these minerals in relation to Mg absorption. We also present frequency distributions for a range of mineral indices that ‘capture' mineral interactions, including the ‘tetany index', forage K: (Na+Mg) ratio and dietary cation–anion difference. It is concluded that the last two indices warrant a much closer investigation. Possible effects of forage aluminium and organic acid contents are briefly discussed; these also deserve closer examination. As research in this area continues, it would be prudent to provide Na and/or Mg supplements for livestock grazing wheat and possibly oats and barley, and calcium supplements for livestock grazing oats or for reproducing animals grazing all three cereals.

The grazing of cereal and canola crops during winter is an increasing component of grazing systems in southern Australia. The capacity of such crops to meet the requirements of young livestock and reproducing animals for sodium (Na), magnesium (Mg), calcium (Ca) and potassium (K) is reviewed. The growth responses of young stock to Na and/or Mg supplements when grazing wheat are discussed. These responses differ from ‘literature expectation’ in that they are rapid in onset and involve no clinical signs. We demonstrate that more insight about the variability in supplement response, both between and between crops species, is obtained when mineral contents are viewed from the perspective of their frequency distributions, rather than their mean values. The pivotal importance of high K concentration, low Na and the resultant K : Na ratio of forage is stressed, as is the interaction of these minerals in relation to Mg absorption. We also present frequency distributions for a range of mineral indices that ‘capture’ mineral interactions, including the ‘tetany index’, forage K : (Na+Mg) ratio and dietary cation–anion difference. It is concluded that the last two indices warrant a much closer investigation. Possible effects of forage aluminium and organic acid contents are briefly discussed; these also deserve closer examination. As research in this area continues, it would be prudent to provide Na and/or Mg supplements for livestock grazing wheat and possibly oats and barley, and calcium supplements for livestock grazing oats or for reproducing animals grazing all three cereals.

In order to increase the concentration of the nutritionally essential sulphur amino acids in seed protein, a transgene encoding a methionine- and cysteine-rich protein, sunflower seed albumin (SSA), was transferred to chickpeas (Cicer arietinum L). Transgenic seeds that accumulated SSA contained more methionine and less oxidized sulphur than the controls, suggesting that additional demand for sulphur amino acids from the expression of the transgene stimulated sulphur assimilation. In addition, the activity of trypsin inhibitors, a known family of endogenous, sulphur-rich chickpea seed proteins, was diminished in transgenic, SSA-containing seeds compared with the non-transgenic controls. Together, these results indicate that the reduced sulphur sequestered into SSA was supplied partly by additional sulphur assimilation in the developing transgenic seeds, and partly by some diversion of sulphur amino acids from endogenous seed proteins. Growth of chickpeas on nutrient with a high sulphur-to-nitrogen ratio increased the total seed sulphur content and the accumulation of sulphur amino acids in the seeds, and partly mitigated the effect of SSA accumulation on the trypsin inhibitor amount. The results suggest that free methionine and O-acetylserine (OAS) acted as signals that modulated chickpea seed protein composition in response to the variation in sulphur demand, as well as in response to variation in the nitrogen and sulphur status of the plant.

Dual-purpose crops can provide valuable winter forage in livestock production systems and increase subsequent pasture availability. Using experimental measurements of sheep grazing on pasture only or dual-purpose crops of wheat, canola, and wheat and canola in combination, and their associated effects on subsequent pasture grazing, we estimated for two different years the whole-farm changes in whole-farm sheep grazing days (SGD), relative farm production and farm economic impact. The increased winter feed supply and higher grazing intensity on dual-purpose crops allowed 2–3 times the area of pasture to be spelled, which together enabled increases in potential year-round pasture stocking rate. Up to 20% of farm area could be allocated to dual-purpose crops while still obtaining the same number of SGD per farm ha with additional grain production (5.0–5.4 t wheat ha–1 and 1.9–3.6 t canola ha–1) adding significantly to farm profitability and production. Allocating 10–20% of the farm to a combination of dual-purpose wheat and canola grazed in sequence could increase whole-farm SGD by 10–15%, increase farm output by >25% and increase estimated farm profit margin by >AU$150 farm ha–1 compared with pasture-only livestock systems. The long crop-grazing period from wheat and canola in combination providing a large pasture-spelling benefit was a key factor enabling these economic and productivity increases. Introducing wheat or canola alone on up to 30% of the farm is likely to reduce SGD per farm ha, but still significantly increase whole-farm productivity (10–20%) and estimated profit margin ($50–100 farm ha–1). Over the two very different experimental growing seasons, the estimated relative changes in whole-farm productivity and estimated profit margin were similar, indicating that these benefits are likely to be consistent over a range of years. Together, these findings suggest that once whole-farm livestock feed-base effects are considered, large economic and productivity benefits can be attributed to dual-purpose crops when integrated into livestock production systems in Australia’s southern high-rainfall zone.

In four experiments conducted in 2006–2008 near Canberra, Australia, young sheep grazed vegetative dual-purpose wheat (cv. Mackellar) while receiving either no mineral supplement or receiving extra sodium (Na) and/or magnesium (Mg). In the first two experiments, supplements were fed to the sheep whereas in Experiments 3 and 4, the extra Mg was applied to the crop just before grazing commenced, either as MgSO4 (Experiment 3, 4) or Causmag (MgO; Experiment 4). Direct supplements of Na resulted in increases of liveweight gain of 20–25% (36–42 g/day). In Experiment 2, sheep consumed significantly less of the mixed Na/Mg supplement than of salt alone (12.0 vs 24.8 g/day; P < 0.05) but still grew significantly faster (61 g/day; P < 0.05) than unsupplemented sheep. Application of supplementary Mg to the crop resulted in significant increases in forage Mg, from levels close to animal requirement (0.10% DM) to levels well above this. It also improved a range of mineral indices related to Mg status. Increases in liveweight gain occurred in response to top-dressing of the crop, but compared with feeding Mg directly to the sheep, these were transient and strongly interacted with stocking rate. Estimates of the cost of supplementation or top dressing, and of the value of the extra liveweight gain obtained, indicated that direct supplementation would be economic, but that top-dressing costs would exceed the value of the extra liveweight gain obtained.

Lambing ewes were grazed on dual-purpose wheat in two experiments in 2010 and 2011 with or without access to a mineral supplement. The calcium, magnesium and sodium content of wheat forage was below the requirements of ewes during late pregnancy and lactation; however, no clinical cases of hypocalcaemia or hypomagnesaemia were observed in either experiment. Blood serum assays identified eight hypocalcaemic ewes and one hypomagnesaemic ewe in Experiment 1, and one hypocalcaemic ewe in Experiment 2, and the provision of a mineral supplement comprising of magnesium oxide, calcium carbonate and coarse salt had no effect on blood magnesium, total calcium, phosphorus or sodium. Lamb birthweight and survival were not affected by provision of the mineral supplement in either experiment; however, the growth rate to marking (mean 38 ± 10 days of age) of twin-born lambs was higher in Experiment 1 when the supplement was provided to ewes grazing wheat (259 vs 243 g/head.day; P = 0.002).

The development of guidelines for successful dual-purpose (graze and grain) use of wheat and canola in Australia’s high-rainfall zones (HRZ) has mostly emerged from separate wheat- and canola-focused research. Less attention has been placed on the benefits of integrating dual-purpose wheat and canola into pasture-based grazing enterprises. We conducted a farming systems experiment during 2010–11 to evaluate the benefits of integrating wheat and canola as dual-purpose crops into a pasture-based grazing system in Australia’s south-eastern tablelands. We compared forage production and grain yield in three separate crop–livestock systems in which the sheep grazed long-season wheat, winter canola or a combination of these. Initial growth rates were higher in early-autumn-sown canola than wheat in 2010, but were much lower although similar in both crops in 2011. Significant forage was available from both canola (3.1–3.4 t ha–1) and wheat (2.3–2.4 t ha–1) at the onset of grazing, but winter growth rates of wheat were higher than those of canola, leading to increased sheep grazing days (SGD). In the favourable 2010 season, dual-purpose wheat and canola separately provided 2393 and 2095 SGD ha–1, and yielded 5.0 and 1.9 t ha–1 grain, respectively, with an apparent nitrogen limitation in canola. In the drier season of 2011, grazing was reduced to 1455 and 735 SGD ha–1 in wheat and canola, respectively. Wheat yield was reduced from 5.9 to 5.4 t ha–1 grain by grazing, whereas canola yield was unaffected (3.6 t ha–1). In both years, grazing did not affect harvest index or oil content of canola, but harvest index was higher in grazed wheat crops. The yield of wheat and canola crops grazed in sequence did not differ from yield in treatments where animals grazed only a single crop, but the total overall grazing window when crops were grazed sequentially increased by 1054 and 618 SGD ha–1 in wheat, and by 1352 and 1338 SGD ha–1 in canola in 2010 and 2011, respectively. The major benefits of including crops that can be grazed sequentially were the widening of the grazing window and other operational windows (sowing, harvest), along with the rotational benefits for wheat by including canola in the system. Additional benefits to pastures may include eliminating the need to re-sow, because a more productive pasture composition is maintained under lower grazing pressure while stock are on crops, and reduced weed invasion. The commercial availability of new, herbicide-tolerant winter canola varieties provides significant opportunities to underpin the performance of dual-purpose crop sequences on mixed farms in the high-rainfall zone.

Two experiments were conducted between 2004 and 2006 near Canberra, Australia, to provide information about herbage intake and liveweight gains of young sheep grazing dual-purpose crop cf. pasture. In an indoor feeding trial (2004–2005), dual-purpose wheat (cv. Mackellar) and oats (cv. Blackbutt) had estimated organic matter (OM) digestibilities of 0.849 ± 0.0070 and 0.847 ± 0.0001, respectively. The indoor trial also provided data for the concentrations and faecal recoveries of the cuticular wax alkane and long-chain alcohol (LCOH) markers used to estimate diet composition and intake in the grazing trial. The faecal recoveries of both alkanes and LCOH were well described by asymptotic regressions. Alkane recovery differed between crops, though not between years. Faecal LCOH recovery did not differ between crops or years. Under grazing conditions in 2004–2005, the OM digestibility (OMD) of crop herbage was 0.825–0.871, significantly higher than the OMD of phalaris-based pasture (0.752–0.758). The estimated OMD of wheat in 2006 (0.792) was lower than in the earlier years. Sheep consumed ~1 kg/day digestible OM intake (DOMI) from crop in 2004–2005. In 2004 this was significantly higher than the DOMI of sheep grazing pasture (0.75 kg/day) whereas in 2005 the DOMI from pasture was slightly (1.15 kg/day) but significantly higher than that from crop (mean 0.97 kg/day). Regardless of the source of herbage consumed, sheep daily liveweight gains were in the range 200–250 g/kg DOMI. Liveweight gains of sheep grazing crop were also predicted from their calculated metabolisable energy intakes and requirements for maintenance and were within 1% of the observed liveweight gains. Our results demonstrate that in high-rainfall areas, the quantity and quality of the herbage provided by sowing dual-purpose crops, and the resultant increased animal liveweight gains, justify the inclusion of dual-purpose crops in grazing systems.

Previous experiments have shown that liveweight gains of livestock grazing dual-purpose wheats were increased by 15–60%, by supplementing animals with a 1 : 1 mixture of Causmag (MgO) : salt (NaCl). The supplement appears to overcome both an Na deficiency in wheat forage, plus a reduced rumen Mg absorption due to a high forage (and thus rumen) K : Na ratio. In crop–livestock systems, there is also renewed interest in grazing forage oats and, more recently, barley and dual-purpose canola. The possible need for Mg–Na supplements for sheep grazing these last three crops was investigated in two experiments near Canberra, ACT. In Experiment 1, sheep grazing wheat, oats, barley and canola were either unsupplemented or received a Mg–Na supplement. There was no significant response to the supplement in sheep grazing oats. After adjustment by covariance for differences in sheep numbers per plot, the difference in weight gain/ha of supplemented and unsupplemented sheep grazing barley approached significance (P = 0.068). For the first time in our experience, in this experiment there was also no significant response in sheep grazing wheat. There was a significant interaction between crop type and supplement, because of a 20% depression in liveweight gain in supplemented sheep grazing canola. This negative effect of supplementation on canola was further investigated in Experiment 2, in which sheep grazing only canola were either supplemented or not supplemented. Supplementation in this case had no significant effect on liveweight gain. Our results suggest that there is no need to provide mineral supplements for sheep grazing dual-purpose oats; they also suggest supplementation may be contraindicated for sheep grazing canola. Further work is needed to confirm this and to clarify supplement responses in sheep grazing barley.

Growing cereal crops for the dual-purposes (DP) of livestock forage during the early vegetative stages and harvesting grain at maturity has been practised for decades. It follows that scientific experiments using DP crops are nearly as old. A survey of more than 270 DP crop experiments revealed that the average effect of crop defoliation on grain yield (GY) was −7 ± 25% (range –35 to 75%). In light of these results, the first purpose of this review was to assess how alternative crop and grazing management regimes affected forage production and GY. Management techniques in order of decreasing importance likely to maximise grain production include (i) terminating grazing at or before GS 30, (ii) matching crop phenology to environment type, (iii) sowing DP crops 2–4 weeks earlier than corresponding sowing dates of grain-only crops, and (iv) ensuring good crop establishment before commencement of grazing. The second aim was to identify the environmental and biotic mechanisms underpinning crop responses to grazing, and to identify crop traits that would be most conducive to minimising yield penalty. A variety of mechanisms increased GY after grazing. Under favourable conditions, increased GY of grazed crops occurred via reduced lodging, mitigation of foliar disease and rapid leaf area recovery after grazing. Under stressful conditions, increased yields of grazed crops were caused by reduced transpiration and conservation of soil water, delayed phenology (frost avoidance at anthesis), and high ability to retranslocate stem reserves to grain. Yield reductions caused by grazing were associated with (i) frost damage soon after grazing, (ii) poor leaf area development or (iii) delayed maturation, which led to water or temperature stress around anthesis, culminating in increased rates of green area senescence and decreased duration of grain-filling. The third aim was to examine the role of simulation models in dissecting the effects of environment from management on crop physiology. Simulation studies of DP crops have extended the results from experimental studies, confirming that forage production increases with earlier sowing, but have also revealed that chances of liveweight gain increase with earlier sowing. Recent modelling demonstrates that potential for inclusion of DP crops into traditional grain-only systems is high, except where growing-season rainfall is

Research is reported probing the concern of some wheat producers that grazing of early sown, dual-purpose wheat for winter forage may accentuate the spread of Wheat streak mosaic virus (WSMV). In experiments with housed sheep, we investigated whether there were any grounds for this concern. In the first experiment, sheep were allowed to graze heavily virus-infected wheat in trays, followed over a period of 24 h by a series of test trays of healthy wheat. The grazed plants were allowed to recover and new leaves were tested for symptoms and the presence of virus. In total, 2352 test plants were negative for WSMV, assessed through symptoms, ELISA, and RT-PCR. In the second experiment, no WSMV particles (assayed with ELISA) or RNA (assayed by RT-PCR) were detected in any saliva samples collected from sheep 0.5, 7.5, and 24.5 h after being fed heavily virus-infected wheat. Furthermore, these saliva samples, when inoculated onto test wheat seedlings under optimal conditions, failed to transmit the virus. In a third experiment we showed that the urea concentration in sheep saliva is at least two orders of magnitude lower than that required to render WSMV non-infective, and therefore is not responsible for the failure of sheep to transmit the virus. Our data provide no support for the suggestion that grazing sheep spread the WSMV between plants in a grazed wheat crop as a consequence of the grazing process itself.

Young crossbred sheep grazed dual-purpose wheat crops in three experiments evaluating the factors affecting variability in liveweight gain. All crops had high crude protein contents [22–33% dry matter (DM)] and in vitro DM digestibilities (0.754–0.876), which would not have limited liveweight gains. Digestibilities measured in vivo in grazing animals were even higher (0.839–0.854). No significant differences were found in preference of sheep for six different wheat cultivars. The diet composition and herbage intake of the sheep were measured in all experiments using plant wax marker profiles. Wheat forage made up 0.88–0.98 of the diet in sheep supplemented with unchopped oaten hay and 0.97–0.99 of the diet in unsupplemented sheep. Total intakes in the first two experiments were ~1380 g DM/day (3.7–4.0% of liveweight). Intakes in Experiment 3 were lower (960–1180 g DM/day; 2.6–3.1% of liveweight) because drought conditions reduced the amount of forage available. There were marked liveweight gain responses (30–50%) to mineral supplements based on NaCl, CaCO3 and MgO. Evidence is presented that these were mainly due to the Na and Mg, since the consumed diet was more than adequate for Ca. Relative to the requirements of young sheep for growth, wheat forage had high K levels (6–8 times requirement) and very low Na levels (as low as 0.02–0.03 of requirement) and thus very high K : Na ratios. Since high dietary K : Na ratios can greatly reduce Mg absorption from the rumen, the response to Na may have been partly mediated through improved Mg absorption. The liveweight gain responses to Na/Mg were large and economic, so it is recommended that young sheep grazing dual-purpose wheat be routinely supplemented with a 1 : 1 mix of NaCl : MgO.

Dual-purpose cereal cropping is gaining acceptance among growers in mixed farming systems. Success in particular seasons depends on management decisions regarding choice of cereal species, sowing date, timing of grazing, and stocking rate. A more detailed understanding of how these factors influence the growth, phenology, and grain yield of the major cereal forages is needed to model these systems. Wheat (cvv. Whistler and Mackellar) and oats (cv. Blackbutt) were grown under dual-purpose management near Canberra, ACT, over 3 years (2004–06) in 2 crop sequences: wheat-oats-wheat and oats-wheat-wheat. In each year, crops were grazed by sheep at low (20/ha), medium (30–35 /ha), and high (40–52 /ha) grazing intensities. In the pre-grazing periods, measurements of phyllochron interval (PI), tiller development rate (TDR), and stem apex height were made. Post-grazing growth rate was determined from shoot biomass cuts taken at the end of grazing and at grain harvest. Soil moisture changes during each year were monitored to examine the pattern of soil water use under varying grazing intensities. In unusually dry periods in March–April 2004 and 2005, oats established significantly denser plant populations than wheat. In 2004, this initial advantage of oats resulted in greater feed on offer at the start of grazing than wheat, whereas in 2005, higher TDR, lower PI of wheat, and the longer duration of tillering resulted in similar amounts of feed on offer at the start of grazing. Elongation of the stem apex was more rapid in wheat than oats, indicating that wheat would be more at risk of damage during grazing. The post-grazing growth rate of wheat and oats was significantly lower than the ungrazed control in the dry spring years of 2004 and 2006, but significantly higher in the wetter spring year of 2005. While reduction in growth rate at high stocking rate was most likely caused by extreme reduction in leaf area, the causes of increases in growth rate following more lenient grazing require further investigation. In 2004 and 2005, there was no significant difference between crops or between stocking rate treatments in soil water depletion during the post-grazing period. However, in 2006, when soil moisture was not affected by rainfall in the post-grazing period, significantly more water was depleted from soil in the 0.60–1.70 m depth under low and medium stocking rate treatments than under the ungrazed control treatment. A gross margin analysis showed greater economic returns for the dual-purpose compared with a grain-only option in each year, most notably in the very dry season in 2006, when conventional practice would have been to sacrifice the grain crop to grazing or hay production.

In southern Australia, winter-born calves may not be at marketable weights until 18 months of age and can thus compete with their dams and the next crop of calves for the pasture resource. We investigated supplementary feeding options to improve calf liveweight gains and overcome this problem. Weaned beef calves confined to feedlots for 70 days were fed different ratios (1 : 1 up to 1 : 4) of sunflower meal to oat grain (Experiment 1) or barley grain (Experiment 2) at levels of 3–6 kg air-dry/day, plus either oaten hay (Expt. 1) or pasture hay (Expt. 2) fed ad libitum. Liveweight gains at 3 kg supplement/day were ~1.2 kg/day at all ratios and were slightly higher at the higher feeding levels. The intake of hay varied inversely with the amount of supplement fed and substitution rates were 0.49 with oaten hay and 0.47 with pasture hay. Total DM intakes did not decline in Experiment 1 as supplement intake increased and increased in Experiment 2 with increasing supplement intake. A separate group of calves that had been grazing mature pasture while their cohorts were in the feedlot showed good compensatory growth when transferred to good pasture, whereas calves coming out of the feedlot onto the same pasture initially lost weight before regaining weight. This suggests that such feedlot-reared calves should be sold direct from the feedlot. In a third experiment, over 2 years, weaned calves grazed mature summer pasture for 81 days and were fed 0, 1, 2, 3 or 5 kg/day of a 1 : 2 ratio of sunflower meal : hammer-milled oat grain. Weight gains were less than in Experiments 1 and 2 and responses of gain to supplement intake were curvilinear. Gains did not exceed 0.75 kg/day and peaked at supplement intakes of 4.3 and 2.8 kg DM/day in years 1 and 2, respectively. Liveweight gains/kg supplement consumed were similar to those in previous studies. A preliminary assessment of supplement costs and the economic value of liveweight gain showed a curvilinear response to supplement intake and suggested that the greatest economic return resulted from an intake of 1.9–2.4 kg/day of the supplement, lower than the supplement intakes for maximum liveweight gain.

The term dual-purpose canola describes the use of a canola crop for forage before seed production. It could potentially provide a profitable and flexible break-crop option for mixed farms, but there have been no studies to test the concept in Australia. We investigated the feasibility of using canola in this way in field experiments near Canberra, Australia, from 2004 to 2006, using European winter and mid–late maturing Australian spring canola varieties. Winter varieties sown from early March to mid-April produced 2.5–5.0 t/ha of biomass providing 0.3–3.5 t/ha of high-quality forage grazed by sheep in winter. The spring varieties produced similar amounts of vegetative biomass from April sowing but were unsuited to the earlier March sowing as they flowered in early winter and did not recover from grazing. The canola forage was readily eaten by sheep; alkane-based estimates of diet composition indicated that >85% of the organic matter intake consisted of canola. Canola forage was also highly digestible (86–88%) and Merino hoggets grew at 210 g/day from a dry matter intake of 1530 g DM/day. The canola generally recovered well when grazed in winter before bud elongation. Delays in flowering associated with heavy grazing ranged from 0 to 4 days when grazed before buds were visible, to 28 days if the crop had commenced flowering. Significant delays in flowering (>14 days) associated with winter grazing did not reduce seed yield or oil content when favourable spring conditions allowed compensatory growth. Yield loss was observed when winter and spring conditions were unfavourable for compensatory growth, or if grazing continued too late into spring (late September) irrespective of seasonal conditions. The yield loss was more than offset by the value of the grazed forage and the mean gross margin for dual-purpose canola over the four experiments was $240 to $500 higher than for grain-only canola depending on the value assumed for the forage. The study indicates there is considerable scope to capture value from grazing early-sown canola crops during winter without significant, uneconomic trade-offs with seed yield. Further investigations in other medium to high rainfall environments in southern Australia are warranted.

We evaluated the integration of a spring forage brassica crop (Brassica campestris cv. Hunter) into a cereal–pasture rotation, as a means of assessing the effects of this practice on the subsequent establishment and grain yield of wheat and oat crops. A brassica crop was grown for lamb production on 0.2 ha plots prepared for dual-purpose cereals, in spring 2003 near Canberra, ACT, Australia. Mackellar winter wheat and Blackbutt oats were sown in the following autumn on the previously sown brassica plots and on plots left fallow over the spring–summer period. A factorial experiment was used to determine the effects of (i) cultivar, (ii) brassica v. fallow, and (iii) grazing on cereal establishment and grain yield. Lamb liveweight gains on brassica over 33 days were rapid (294 g/day) and provided 2141 grazing days/ha and 637 kg lamb weight gain/ha. Average grain yield of Mackellar on plots following brassica (2.8 t/ha) was reduced by 29% compared with plots following fallow. Average grain yield on grazed plots (2.6 t/ha) was reduced by 38% compared with ungrazed plots. In both Mackellar and Blackbutt, reduced numbers of kernels per spike and reduced kernel weight accounted for the reduction in grain yield under grazing. Two other experiments were conducted at a separate site to obtain data on the nutritive value of the cereal forages and to record phenological development of the two cereals and compare grain yield responses to cutting before and after stem elongation stages. In vitro and in vivo measurements of digestibility in the vegetative phase were similar in the two cereals (91–94%). Grain yield was significantly reduced following cutting at the post stem elongation stage in Mackellar and Blackbutt and, in Mackellar, was attributable to reduced kernel number per spike and kernel weight. The overall economic return, combining actual returns from lamb production on the forage brassica, and estimated returns from grazing and grain production, after variable costs of each phase were accounted for, were $1117/ha for Mackellar wheat and $1081/ha for Blackbutt oats. These returns were $583/ha and $910/ha more than the estimated return from the fallow, ungrazed treatments for wheat and oats, respectively.

The feeding of known amounts of supplements to grazing animals can be accomplished relatively easily. If the supplement and the other diet components have distinctive profiles of cuticular wax n-alkanes, then the supplement intake and the alkane profiles of the supplement, other dietary components and faeces can be used to estimate the proportions and hence intakes of several forages by the grazing animal. However, this method requires knowledge of recoveries of n-alkanes in faeces. Twenty four wethers were fed one of four diets comprising equal combinations of 1, 2, 3 or 4 forages. Forages used were subterranean clover, phalaris, annual ryegrass and wheat straw. Forages were chopped using a chaff cutter and fed with solvent-extracted cottonseed meal (CSM) labelled with beeswax and synthetic C28 alkane to provide a characteristic alkane profile. Faecal grab samples were taken from sheep from 14 to 23 days after administration of an intra-ruminal controlled-release device (CRD) containing 1 g of each of C32 and C36 alkane. Total faeces were collected from half the sheep on each treatment in order to measure alkane recoveries in individual sheep. Faecal concentrations of the n-alkanes C25 to C31 and C33 were corrected for recovery using the individual sheep value, the treatment mean or the grand mean for all four treatments. Dietary compositions were then estimated from corrected faecal concentrations of n-alkanes using a least-squares procedure and, together with the known supplement intakes, were used to estimate the intakes of all other diet components. Estimates from this ‘labelled supplement’ method were compared with the amounts fed or those estimated using the alkanes derived from the CRD. The labelled supplement method accurately and precisely estimated dietary component proportions and intake for all treatments when measured recoveries for individual sheep were used. Precision declined when recovery was based on estimated recoveries for treatment means or the grand mean. Estimates of intake based on dietary C33 and the measured release rates of C32 or C36 alkanes from the CRD did not differ from measured intakes. Estimates based on the C32 : C31 alkane pair over-estimated intake. Estimates of whole-diet digestibility based on the various ways of estimating intake were all very close to the digestibilities calculated from directly-measured intakes and faecal outputs. It is concluded that the feeding of a known amount of supplement can be successfully used to estimate dietary proportions and hence intakes of diet components, in mixed diets with up to five ingredients, but this approach requires estimates of faecal alkane recovery.

Two experiments were conducted to evaluate factors influencing the release rate of octacosane (C28) and dotriacontane (C32) synthetic alkanes from controlled-release devices (CRD) inserted into the rumen of sheep, and the resultant accuracy of alkane-based estimates of herbage intake. In the first experiment, estimates of the rate of release of alkanes from CRD suspended in the rumen of 7 rumen-fistulated ewes were obtained by directly measuring the rate of CRD plunger travel. In the second experiment, CRD were administered orally to 24 castrate male sheep to evaluate the effects of level of feeding (1200 v. 600 g DM/day), frequency of feeding (continuous v. once-daily), and number of CRD inserted (1 v. 2) on temporal trends in faecal alkane concentrations and ratios and on the accuracy of estimation of intake. In both experiments, animals were also dosed orally, once daily with paper pellets containing 56 mg hexatriacontane (C36). In Expt 1, linear alkane release from the CRD commenced after a lag period of 2-3 days, at mean rates of 40.1 mg/day (C28) and 41.7 mg/day (C32), close to the desired rates of 40 mg/day. There was no evidence of curvilinearity, and differences in release rate between sheep were small (CV 4.1%). Alkanes attributable to the CRD appeared in faeces after 2-3 days and reached plateau concentrations by 6-7 days. Data are presented to indicate that the release rate was not affected by the removal of CRD from the rumen for measurement, and that the release rates in fistulated (Expt 1) and intact sheep (Expt 2) were similar. In Expt 2, there was no effect of level of feeding on CRD release rates and faecal alkane concentrations were consistent with the differences in faecal output caused by feeding level. As a result, the accuracy with which known intakes were estimated was unaffected by level of feeding. Similarly, there were no effects of feeding frequency on the accuracy of estimated intake, implying that in this study, feeding frequency had no effect on CRD release rates. The administration of 2 CRD to half the animals in this experiment increased faecal concentrations of C28 and C32 and the synthetic : herbage alkane ratios associated with these alkanes [e.g. faecal C32 : tritriacontane (C33)] but these changes were not significantly different from those expected from the release rates estimated in Expt 1. As a result, the accuracy with which known intakes were estimated was not influenced by the number of CRD administered. In both experiments, once-daily dosing with C36 alkane resulted in a more rapid rise in faecal C36 concentrations and faecal C36 : pentatriacontane (C35) ratios to maximal levels (3-4 days), compared with alkanes derived from the CRD (6-7 days), but thereafter, faecal C36 concentrations were much more variable, especially in the fistulated sheep. As a result, intake estimates based on the C36 : C35 alkane pair significantly over-estimated known intakes by 13% (Expt 1) and 8% (Expt 2). Data are presented to indicate that C36 alkane functioned satisfactorily as a faecal output marker and, with C32 : C33 estimates of intake, provided accurate estimates of herbage digestibility. The results indicate that intra-ruminal controlled-release devices provide a satisfactory means of delivering an accurate, daily dose of alkanes for the estimation of herbage intake, faecal output, and digestibility in sheep.

A short-term shading treatment was used to create a Phalaris aquatica L. pasture with alternating strips of ‘low’ [62 mg/g dry matter (DM)] and ‘high’ (126 mg/g DM) water-soluble carbohydrate (WSC) concentration. Analyses showed that starch and all components of the WSC were reduced in concentration by shading. The shaded and unshaded pasture strips did not differ significantly in in vitro DM digestibility (84% DM), nitrogen (3.1% DM), or neutral detergent fibre concentration (42.4% DM). Synthetic alkanes were applied to the pasture strips as markers to measure the selection of the shaded and unshaded pasture by sheep. When 12–13-month-old Merino wethers were given simultaneous access to both pasture treatments, they selected 2.6-fold more unshaded (high WSC) pasture than shaded pasture. The results indicate the involvement of herbage total WSC and its components in the process of diet selection by sheep, and suggest that in future studies, more attention should be paid to reporting data for total WSC concentration.

The concentrations of water-soluble carbohydrate (WSC) and its components, starch, total nitrogen, and dry matter of phalaris (Phalaris aquatica L. cv. Australian) pasture were varied by shading for periods ranging from 38.5 to 46.5 h. In unshaded pasture, WSC concentrations were lowest at sunrise [103 mg/g dry matter (DM)] and increased until early afternoon (to 160 mg/g DM). Sucrose and starch increased in concentration during daylight, whilst the concentrations of glucose, fructose, fructan, and a component of WSC considered to be mainly the carbohydrate moiety of glycoside(s) were relatively constant. The concentrations of starch, and all components of WSC except sucrose, were reduced by shading, but increased to the concentrations observed in the unshaded pasture within 2–4 h after removal of the cover. The fructans present in phalaris were determined to be oligosaccharides of degree of polymerisation (DP) 3 and DP 4 and high molecular mass fructans with DP >10. Nitrogen concentration of shaded pasture was initially higher (4.7% DM) than in unshaded pasture (3.9% DM), but decreased after removal of the shade cover. Dry matter content was reduced in shaded pasture, partly due to increased retention of water on the exterior of plants. The experiment was a precursor for a grazing trial in which the WSC content of pasture was to be altered by shading. It indicated that shading would potentially alter WSC and N concentrations, and DM content, but would have only a relatively small impact on the digestibility of the pasture.

The n-alkane and chromium/in vitro procedures for estimating herbage intake were compared in grazing ewes during late pregnancy, early lactation, and mid-lactation. To ensure differences in herbage intake, the ewes were grazed in 4 plots of phalaris-dominant pasture at 2 levels of stocking: 17.1 ewes/ha and 30.8 ewes/ha. To investigate whether either procedure for estimating herbage intake was influenced by supplement consumption, half of the ewes at each stocking level received 500 g/day air-dry of a pelletted supplement (1 : 1 milled oat grain : sunflower meal). Supplement intakes were estimated using tritiated gypsum as a marker. During intake measurement periods, ewes were dosed twice daily with both alkane capsules and capsules containing chromium sesquioxide. For the last 6 days of the 12-day dosing period, rectal faecal samples were taken twice daily, immediately before the dosing. Over these same periods, wether sheep fitted with faecal collection harnesses were similarly dosed and sampled, and their total faecal output collected to establish the faecal recovery of chromium and the alkanes. Herbage intakes were estimated using the C27/C28, C29/C28, C31/C32, and C33/C32 alkane pairs. Estimates of intake based on the shorter alkane pairs were lower than those estimated with the C33/C32 alkane pair, by amounts which differed between the periods. Evidence is presented that estimates based on the last pair of alkanes (C33/C32) are the most accurate and are also more accurate than those based on the chromium/in vitro procedure. The relationship between these 2 methods for estimating intake was different in mid-pregnancy compared with either stage of lactation. The consumption of supplement did not interfere with any of the methods for estimating herbage intake. Estimates of faecal output based on the use of chromium, C28 alkane, or C32 as an external marker were statistically identical, indicating that the difference between the 2 methods for estimating herbage intake was not related to a failure to accommodate the incomplete recovery of any of the markers used or to the failure of rectal grab samples to be representative of total faeces. Our results indicate that herbage collected by oesophageally fistulated (OF) sheep was representative of that grazed by the ewes and could thus be used to provide the herbage alkane data needed to estimate herbage intake by the alkane method. However, the in vitro digestibility values obtained from the OF samples did not represent the digestibilities actually occurring in vivo. This was the main cause of the observed difference between the 2 methods for estimating intake. Possible reasons for the differences between the in vitro and in vivo estimates of digestibility are discussed.

Annual grass pasture (mainly annual ryegrass) was treated at seed head emergence (12 October 1990) with the herbicide glyphosate to delay loss of digestibility during late spring and summer. The lowest rate of glyphosate application needed to retain a high digestibility in the dry matter (DM) of the senescent grass sward was 180 g a.i./ha. The in vitro DM digestibility of control (unsprayed) pasture declined rapidly from relatively high levels near anthesis (28 October) (77n86%, leaves and seed head; 66%, stems) until about 38 days after anthesis (51n71%, leaves and seed head; 24%, stem). Thereafter, the digestibility of the plant parts did not change appre- ciably over at least 4 months. Treatment with glyphosate significantly slowed the loss in digestibility of stem, leaf sheaths, and seed head but did not affect the decline in digestibility of leaf blades. For example, the digestibility of stem in the sprayed pasture was 26 percentage units higher than that in the control pasture 38 days after anthesis. If the time at which digestibility of stems reached 50% is taken as an indication, the effective delay in loss of digestibility was of the order of 5 weeks. However, improved digestibility in the treated pasture was achieved at the expense of pasture yield, with the peak yield of control pasture being 4 t DM/ha (45%) higher than that of the treated pasture. Improved digestibility in treated grass pasture was mainly associated with delayed loss of water-soluble carbohydrates (WSC), except in the seed head. Improved cell wall (neutral detergent fibre) digestibility also con- tributed to varying degrees and was the main factor contributing to improved digestibility in the seed head. The major WSC present in the treated pasture was fructan. The crude protein concentrations of all plant parts of the senescent pasture, except the leaf blades, were also increased by treatment with glyphosate. Additional keywords: annual ryegrass, digestibility, fodder, fructans, herbicide, Lolium rigidum, senescent pasture, soluble carbohydrates.

The treatment of annual ryegrass–silver grass pasture with the herbicide glyphosate at seed head emergence delayed the loss of soluble carbohydrates and improved herbage digestibility. The present study investigated whether this improvement in nutritive value had any influence on the diet preference, intake, and performance of housed sheep. Since the effects of glyphosate on digestibility were most marked in stem tissue, preference was examined not only in relation to sprayed v. unsprayed herbage, but also in terms of preference for individual plant parts. In the preference testing, sheep showed a marked preference for sprayed rather than unsprayed herbage. They also consumed more of it, such that their digestible dry matter intake from sprayed herbage was nearly twice that from unsprayed herbage. When sheep were offered different plant fractions from the control herbage, they selected against stem material and preferred leaf or seed head. By contrast, when offered fractions from the sprayed material, they preferred stem to leaf, but showed no strong preference for stem over seed head. Preference was related more to the soluble carbohydrate content of a plant part than its digestibility, and only when soluble carbohydrate contents were similar was there preference for the more digestible material. The consumption of sprayed herbage, compared with control herbage, led to higher concentrations of rumen volatile fatty acids in the period 4 h after feeding. Moreover, the feeding of these herbages over a 6-week period resulted in significant reductions in pre-feeding plasma urea and β-hydroxybutyrate concentrations. When control herbage was fed with supplements of fructose, urea, or fructose+urea, in an attempt to mimic the possible differences in nutritive value between control and sprayed herbage, the responses in rumen and blood metabolites were less marked than when sprayed herbage was fed. As a consequence of the higher nutritive value of the sprayed herbage and the higher intakes by the animals fed this material, sheep fed sprayed herbage were able to maintain weight over the feeding period, whereas those offered the control herbage lost weight at 130–150 g/day

Previous papers in this series have demonstrated that, when annual pastures were sprayed at seed head emergence with low rates of the herbicide glyphosate, the nutritive value of the sprayed herbage was improved. Housed sheep preferred sprayed herbage to unsprayed herbage and, within sprayed herbage, appeared to have a preference for stem material. The housed sheep ate more of the sprayed material and their weight gains were improved. If such responses occurred in grazing animals, they could result in substantial improvements in animal liveweights or wool production. The present paper describes the alkane-based procedures used to investigate diet selection and herbage intake in grazing animals, with the emphasis placed on methodological and statistical issues. The alkane concentrations in the plant fractions (leaf, leaf sheath, stem, seed head) of sprayed and unsprayed herbage are reported. Similarly, the alkane concentrations in extrusa samples collected by oesophageally fistulated sheep given access to the grazed areas, and in the faeces of sheep grazing the areas, are reported. Patterns of alkane concentrations in extrusa and faeces were similar and indicated that, in the short term, oesophageally fistulated animals consumed a diet of similar composition to that selected by the animals resident on the plots. Using these data for alkane concentrations, multivariate statistical analyses are presented which provide an objective basis for selecting the alkanes to be used in the estimation of diet selection. The results of the first of 4 grazing periods are presented, as an example of the application of the alkane-based procedures for estimating herbage intake and, in particular, diet composition. Use of these techniques indicated that, when given access to sprayed senescent pasture, sheep consumed more digestible dry matter and selected more of it from the stem fraction than was the case with unsprayed herbage. These results are similar to those found with housed animals and demonstrate that patterns of herbage and faecal alkane concentrations can be used to estimate diet composition of grazing animals in terms of the plant parts on offer

We report the effects of spray-topping annual grass pasture with glyphosate (180 g a.i./ha as Roundup CT, at the seed head emergence stage) on the nutritive value of herbage and on subsequent performance of grazing sheep. Eight 1-ha plots, consisting of 4 sprayed and 4 unsprayed (control) plots, were set-stocked with Merino wethers (18 months old, 12 sheep/ha) from 8 days after anthesis in the control plots (late spring) until 165 days after anthesis (mid-autumn). In 4 periods (15–20, 36–41, 71–76, and 99–104 days after anthesis; Periods 1–4, respectively) sheep were dosed with synthetic alkanes and herbage and faecal samples were taken, in order to estimate diet composition (in terms of plant parts), faecal output, herbage intake, and the digestibility of the whole diet. As described in our earlier papers, spray-topping reduced the yield of pasture dry matter, but also slowed the loss of water-soluble carbohydrate (WSC) and digestibility during pasture senescence. The present paper shows that as a result, sheep grazing sprayed herbage in Periods 1 and 2 consumed significantly more organic matter (OM) and digestible OM (DOM) than sheep grazing the control pasture. Their diet contained a higher proportion of stem with a higher WSC concentration than that of the sheep grazing the control plots. The proportions of different plant parts (leaf blade+sheath, stem, seed head) in the diet of both the plot sheep and oesophageally fistulated (OF) sheep, which grazed treatments for short periods, differed significantly between treatments in all periods. However, the compositions of the diets selected by plot and OF sheep were similar. These results confirmed diet preferences measured using housed sheep and demonstrate the usefulness of alkane-based procedures for quantifying diet composition and intake in grazing animals. As a result of their higher intake of DOM, sheep grazing sprayed herbage had a significantly higher liveweight gain over the first 2 periods (40 g/day). In Period 3, sheep grazing sprayed herbage consumed more OM than sheep grazing control herbage. However, DOM intakes from sprayed or control plots were not significantly different in either Period 3 or Period 4, and were lower than in Periods 1 and 2. Sheep grazing both treatments lost liveweight at a similar rate over this time. Wool growth in sheep grazing sprayed herbage was improved by 10% during the experimental period; wool strength was also improved significantly. The implications for the management of sheep grazing spray-topped pastures over summer are discussed.

Plants of the pasture species Phalaris aquatica cv. Sirosa, Lolium perenne cv. Victorian, Trifolium repens cv. Irrigation White, T. subterraneum ssp. subterraneum cv. Mt Barker, T. subterraneum ssp. yanninicum cv. Trikkala, and Medicago sativa cv. Siriver were grown under controlled glasshouse conditions. At weekly intervals, 6 plants of each species were harvested and dissected into their component plant parts. The concentrations of n-alkanes in plant parts from all species were then estimated using gas chromatography. Results confirmed earlier studies that alkanes with odd-numbered carbon chains were predominant in cuticular wax, especially C27, C29, C31, and C33 alkanes. For the individual alkanes (225433, differences between species accounted for 85% of the total variance in alkane concentration. Calculation of similarity coefficients indicated that the greatest similarities in the pattern of alkane concentrations occurred either between plant parts within a species or between the same plant part in closely related species. Multivariate statistical analysis using canonical variates analyses indicated that despite these similarities, it would still be possible to distinguish both plant species and plant parts in mixtures of these components. In particular, an examination of hypothetical perennial ryegrass-white clover or phalaris-subterranean clover pastures demonstrated that all fractions of all species would be likely to be distinguishable. The results are discussed in relation to the use of herbage and faecal alkane concentrations in least-squares estimates of the composition of the diet of the grazing animal.

The existing mathematical methods for estimating botanical composition of an animal's diet from the concentrations of plant alkanes in herbage and faecal samples all have significant limitations. These include the need for an arbitrary selection of a subset of alkanes for use in the calculations, the loss of information, or the generation of negative estimates for diet components when more than two species are present. We present a new algorithm for solving the diet composition problem, which overcomes these difficulties and is rapid to compute. This algorithm (known as non-negative least squares-NNLS) is shown to perform as well as previous methods on a set of herbage mixtures of known composition. Issues relating to the estimation of the errors of diet composition estimates are discussed.

Over 3 years, we examined the possible benefits of moving the joining date from mid March to early February for the productivity of a prime lamb system based on Border Leicester x Merino ewes on the southern tablelands of New South Wales. The proportion of ewes with >1 lamb (fertility) was affected more by year and by age of ewe than by joining date. The mean proportion of fertile ewes with >1 lamb (fecundity) was reduced from 0.28 to 0.15 at the earlier date, while immunisation against androstenedione increased fecundity at both mating times to 0.42 but significantly reduced fertility in the earlier group. Over the 3 years, the earlier joining produced 12 fewer lambs per 100 ewes mated and immunisation increased lamb number by 17, but flushing (for 3 weeks with sunflower meal) had no significant effect. Immunisation did not have a consistently greater effect at the earlier joining. Groups of these ewes, balanced for fetus number, grazed at 6.5, 10, or 13 per ha on pastures based on phalaris and subterranean clover. Ewe liveweight after lambing, lamb birth weight, and perinatal mortality were not affected by joining date, but mean daily weight gain by later born lambs over the first 90 days of life was 44 g greater than for earlier born lambs. However, earlier joining enabled 17 more lambs per 100 ewes to reach a marketable weight of 31 kg within the pasture season. Twins grew more slowly and relatively few reached sale weight. With a mean 1.4 lambs per ewe, the optimum stocking rate on these pastures appeared to be 6.5-10 ewes/ha. Superphosphate application to half of the experimental area, after 17 years without treatment, increased pasture weight, lamb growth rate, and numbers sold. The increase was such that a treated pasture could have carried an extra 3 ewes/ha without depression in individual productivity, relative to an untreated pasture. Supplementation of ewes in late pregnancy and early lactation benefited only twin lambs at the higher stocking rates. The results suggest that a prime lamb system in this environment is more likely to succeed with the earlier joining date. The lower lambing percentage, resulting from a decrease in fecundity, is likely to be of benefit, rather than detriment, to the efficiency of a system in which single- and twin-bearing ewes and their lambs are given equivalent treatment.

SummaryWeaned cross-bred lambs either grazed mature pasture or were confined to yards where they were offered material cut from ungrazed areas of the same pasture. A 1:2 mixture (on an air-dry basis) of sunflower meal and oat grain was offered for 81 days at 0, 200, 400 or 600 g/head or ad libitum. Individual estimates of intake of pasture and supplement by grazing sheep at four levels of supplementation were made on four adjacent plots.Weight gain increased from –30 to 178 g/day in the grazing animals as supplement intake increased up to 1030 g D.M./day and from –25 to 142 g/day in the yarded animals as supplement intake increased to 1076 g D.M./day. Growth of greasy wool increased from 4·5 to 11·7 g/day for grazing animals and from 4·5 to 10·2 g/day for those kept in yards.At levels of supplement intake below 400 g D.M./day, the intake of grazed pasture increased by up to 58% compared with unsupplemented animals. However, when the intake of supplement was increased to about 650 g D.M./day, pasture intake fell, with an estimated substitution rate of 1·1 g D.M. pasture per g D.M. supplement. At all levels of supplementation, the intake of hay by the yarded lambs was less than half the intake of herbage in the field. However, at levels of supplement intake between 300 and 500 g D.M./day, the substitution rate was similar to that measured in the grazing animals, suggesting that this is an attribute of roughage quality, rather than differential eating behaviour between grazing and yarded animals.The wastage, w (g D.M./day), of supplement was linearly related to the amount offered, s (g D.M./day), by the equationw = 0·263s − 38·8; R2 = 0·89Variability in supplement intake between individual grazing lambs was not affected by the level of supplementation but the coefficient of variation of supplement intake was considerably greater than that of the intake of unsupplemented pasture. Variability in the intake of pasture increased with the level of supplementation but variability in the total intake of food was similar at each level of supplement, indicating some degree of individual compensation in the intake of the two components.