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Temperate pastures for grazing livestock
Abstract
This series of papers reviews the literature and reflects on those characteristics of temperate pastures and their management that influence grazing value and sustainability. In temperate environments, pastures provide the primary feed resource for extensively managed livestock. Evidence for the superiority of improved legume-based pastures compared with indigenous pastures is well established; pasture management guidelines that achieve profitable and sustainable livestock systems are well developed; and plant breeding is developing new pasture varieties with genetic improvement in attributes that confer enhancements to seasonal yield, nutritive value and product quality. However, previous pasture research has been undertaken in the context of in situ input-output relationships, and it is proposed that future research needs to broaden its scope to account for impacts on the soil, plant and livestock resources in the wider pastoral landscape.
... Although pasture improvement based on white clover and superphosphate in Australia during the 1950s and 1960s was very successful (Ayres and Lloyd Davies 2000), by the early 1980s poor clover persistence and high herbage yield fluctuations emerged as major problems, especially in summer rainfall environments (McDonald 1988). This lack of reliability, particularly in marginal environments with commercially available white clover cultivars, is attributed to poor persistence (Gillard et al. 1989;Kenny and Reed 1984;Robinson and Lazenby 1976). ...
A breeding project has developed a new synthetic white clover (Trifolium repens L.) cultivar, Grasslands Trophy, that possesses tolerance of summer moisture stress in dryland pasture environments in the 850-1250 mm average annual rainfall temperate perennial pasture zone in eastern Australia. The breeding strategy used to develop Grasslands Trophy was an in situ breeding cycle for: (i) identifying and selecting superior genotypes, (ii) crossing elite germplasm and (iii) progeny testing derived breeding lines for the expression of key agronomic and grazing value traits. The primary selection criteria were early vigour, herbage yield, persistence and seed yield potential. Parental selection was also applied for seed yield, uniformity of leaf size, uniform flowering pattern and freedom from disease and virus symptoms. Grasslands Trophy is medium-large in leaf size with stable leaf size, combines intermediate stolon density with intermediate stolon thickness, and expresses high stolon survival and strong autumn regrowth following summer moisture stress. Grasslands Trophy has mid-season flowering maturity, intensive flowering prolificacy and high seed yield capability. Agronomic results from trials in northern New South Wales and New Zealand indicate that Grasslands Trophy has broad adaptation, expresses high summer and winter growth activity, and is reliably persistent for at least 4 years.
Increased taproot diameter is an important component in maintaining white clover (Trifolium repens L.) growth, nitrogen fixation and persistence during short-term moisture stress. Previous reports indicated selection for large taproot diameter would result in commensurate increases in leaf size and poorer growth habit. The current research investigates the response to selection for taproot diameter and the association between taproot diameter and leaf size in large-leaved clovers suited to dairy grazing systems. Taproot diameter increased by 2.4% per cycle while leaf size and growth habit were not significantly altered. Furthermore, while taproot diameter did not increase between cycle 2 and 3, the root index which measures the ratio of taproot diameter to leaf size increased linearly across all three cycles. These results suggest it is possible to select white clovers for dairying which have larger taproot diameter while maintaining a suitable growth habit. Keywords: dairying, drought, genetic improvement, root morphology, Trifolium repens L., white clover
Better persistence and reliability of white clover (Trifolium repens L.) is critical in achieving a more competitive New Zealand farming industry. To persist, white clover must establish well and withstand the accumulated stresses of competition from associated grasses, grazing, variable soil fertility, drought, plus pest and disease pressure. These factors vary markedly with environment and farming system, making the choice of appropriate grazing management, plant nutrition, companion species and cultivar difficult. White clover is particularly vulnerable to mismanagement and environmental stresses during spring when plant size is at its smallest. This vulnerability is further compounded by the current trend in dairying to apply high rates of nitrogen (N) which favours grass growth more than clover growth. A faster grazing rotation and/or higher stocking rates can offset the adverse effects of N on white clover by utilising the additional grass produced and reducing competition for light. Irrespective of N inputs, frequent defoliation during spring favours white clover persistence by increasing grass tiller density, resulting in better ground cover and in lower soil surface temperatures in summer. There is a threshold above which the density of associated grass suppresses clover growth. This is most prevalent in swards containing browntop, cocksfoot and kikuyu, which are more competitive against white clover than tall fescue, timothy and perennial ryegrass. Plant breeding efforts to improve persistence concentrate on increasing the rate of stolon formation and decreasing the rate of stolon death. These efforts include selecting genotypes that have better spread and persistence in association with different grasses, and genotypes that continue to grow with lower inputs of phosphate. Changes in root morphology have enhanced persistence under moderate drought stress, while significant improvements in resistance to clover cyst nematode, root-knot nematode and clover flea offer real hope in reducing the impact of these pests. Developing cultivars with higher stolon growing point densities at a particular leaf size should improve persistence while maintaining the greater yield potential. Keywords: climatic stresses, competition, diseases, grazing management, pests, plant breeding, plant nutrition, Trifolium repens L.
Selections were made within Trifolium repens cv. Grasslands Huia for genotypes tolerant and susceptible to aluminium (Al). Three tolerant and 3 susceptible genotypes were crossed in a diallel design, with reciprocals bulked. Progenies were compared with Huia, the 6 parent genotypes and Lotus pedunculatus cv. Grasslands Maku for Al tolerance in soil. All genotypes selected for tolerance were more tolerant to Al than the susceptible genotypes. Similarly, the progeny from crosses between tolerant genotypes were more tolerant to Al than progeny from crosses between susceptible genotypes. Differences between genotypes for general combining ability for Al tolerance were significant at 300 and 400 ppm Al, but differences between crosses for specific combining abilities were not significant. Crosses between tolerant and susceptible genotypes showed that Al-tolerance was a recessive character in white clover. Although narrow sense heritabilities were moderately high, transfer of Al tolerance by hybridisation within white clover would be less successful than selection within a population because of the recessive nature of this character.
We identify three major components of spatial variation in plot errors from field experiments and extend the two-dimensional spatial procedures of Cullis and Gleeson (1991) to account for them. The components are nonstationary, large-scale (global) variation across the field, stationary variation within the trial (natural variation or local trend), and extraneous variation that is often induced by experimental procedures and is predominantly aligned with rows and columns. We present a strategy for identifying a model for the plot errors that uses a trellis plot of residuals, a perspective plot of the sample variogram and, where possible, likelihood ratio tests to identify which components are present We demonstrate the strategy using two illustrative examples. We conclude that although there is no one model that adequately fits all field experiments, the separable autoregressive model is dominant. However, there is often additional identifiable variation present.
A perennial ryegrass breeding pool showed significant genetic variation for concentrations in leaf of 8 of 16 macro- and micro-nutrients measured. Narrow sense heritabilities (h²) ranged from 0 (B, Zn) to 0·9 (Mn, Na). Families selected for high and low herbage P concentrations (h² = 0·4) showed consistent behaviour over a range of soil P treatments in a separate experiment. Families similarly selected for herbage K concentrations (h² = 0·15) did not show such consistent response in a later experiment. High soil K reduced herbage Mg concentrations, but family means for herbage Mg and herbage K concentrations were not correlated. The data show that selection for herbage content of Mg, Na, or P is likely to be successful, but that herbage K is not simply regulated. These results have implications for livestock Mg metabolism, for efficiency of P and K use in mixed legume-based pastures, and for P and K wastage from pastures.
Substantial genetic gains have been achieved across a range of temperate forage grass and legume species in New Zealand during the past 60 years. The genetic gains reported here compare favourably with those achieved in cereals and with those achieved for similar species internationally. Substantial improvements in grain yield of cereal crops have been achieved through changes in harvest index; however, increases in yield of forage grasses and legumes reflect increases in total above ground biomass. Rates of genetic gain have been lower in lucerne (Medicago sativa L.) than in red clover (Trifolium pratense L.) and white clover (Trifolium repens L.) and lower in perennial ryegrass (Lolium perenne L.) than in annual ryegrass (Lolium multiflorum Lam.) and tall fescue (Festuca arundinacea Schreb.). Gains in forage yield and quality have often exceeded 1% per year and have led to significant (0.3 to 1.3% per year) increases in animal performance.
Liveweight changes were measured for lambs grazing six high endophyte perennial ryegrasses, in a grazing experiment run by an independent research organisation in Canterbury, New Zealand. Ryegrass cultivars were sown under code in a binary mix with white clover in February 1997. Plots were strategically irrigated to avoid moisture stress, and stocked at approximately 27 Coopworth ewe lambs per ha in May 1997. Common pasture residual mass was maintained across cultivars by strategic addition of extra lambs, with extra grazing days recorded for each replicate. Lamb liveweight gains and botanical composition of replicates were assessed quarterly. Lamb liveweight gains differed significantly between treatments in Years 1 and 2 of this ongoing 3 year study. Lambs grazing 'Quartet' tetraploid perennial ryegrass gained, on average, 37.4 kg and 36.1 kg liveweight during Years 1 and 2 respect-ively, and together with 'Aries HD' (35.0 and 35.9 kg) produced significantly greater liveweight gain compared with 'Grasslands Nui' (22.0 and 23.7 kg) and 'Bronsyn' (22.5 and 24.1 kg), LSD0.05 = 6.0 and 7.4. Lambs grazing 'Embassy' gained 31.6 kg and 28.7 kg, and 'Vedette' 29.8 kg and 28.0 kg. Extra grazing days expressed as a per-centage of base grazing days were between 3.8 and 6.7% across cultivars for Year 1 and between 2.0 and 6.5% across cultivars for Year 2. This study demonstrated significant differences in animal productivity between perennial ryegrass cultivars that produce comparable yields of dry matter. Differences may reflect variation in forage quality, endophyte toxins, clover content in the sward or other unidentified cultivar characteristics.
The experimental area was located at the Big Ridge 2 site, CSIRO, Chiswick (30°31′S, 151°39′E), 20 km south of Armidale, New South Wales, Australia. The site was established in 1955. In March 1966, phalaris and white clover were sown and pastures were fertilised annually with superphosphate until 1993. There were 3 pasture treatments, each with 2 replicates: degraded pasture (low phalaris content), phalaris dominant, and phalaris–white clover. Each of 6 experimental plots was divided into 3 strata. Two representative areas 1 m by 0.5 m were selected in each stratum of each treatment. The selected areas were labelled with ³⁴S-enriched (90%) elemental sulfur and ¹⁵N-enriched (99%) NH4Cl solution. All plots were grazed continuously by sheep.
No effect of pasture type on N leaching was apparent in this experiment. Seasonal variation of total soil mineral N in different soil layers, low ¹⁵N recovery down to 60 cm soil depth, and low nitrate-N concentrations in drainage water obtained in this experiment suggest that synchronisation of pasture growth with mineralisation and nitrification, together with ammonium domination of the soil N system, is the key ecological feature in preventing N leaching in this environment.
Unlike N, potential S leaching was found with evidence of a large amount of sulfate stored deeper in the soil profile and high S concentrations in drainage water. High KCl-40 extractable S concentration in the top 20 cm soil layers was associated with the long history of superphosphate application. Long-term applications of superphosphate (1967–93), together with an increase in sulfate sorption capacity at lower soil depths, resulted in a large amount of sulfate stored at greater depth. However, retention of the ³⁴S applied in 1995 in the top 10 cm soils suggests that sulfate-S movement down the soil profile is slow.
An experiment was conducted at Armidale, New South Wales to evaluate the persistence and productivity of 6 perennial grasses under 2 defoliation severities and a range of moisture/drought conditions created using a rain-out shelter. Defoliation was either moderate or severe whilst the moisture/drought conditions imposed included a non-stressed moisture treatment, and seasonal droughts simulated as 40-percentile (40-P) and 10-percentile rainfall (10-P). The treatments were applied over 2 experimental seasons; spring–summer and summer–autumn. A range of measurements was taken including plant mortality, basal area, foliage greenness, herbage mass, growth rate and digestibility. Some of these results were then used as inputs to the GrazFeed decision support system to predict liveweight gain and wool growth rate from pastures growing under such conditions.
Plant mortality of over 40% was observed in Dactylis glomerata and Lolium perenne under moderate (40-P) drought conditions during spring–summer. In contrast, under severe drought conditions (10-P), less than 20% of plants died, suggesting that, when combined with defoliation stress, a more common drought can present a greater hazard to plant persistence than a severe drought during spring–summer. Plant mortality was reduced and non-significant when subjected to the summer–autumn drought treatments.
Plant growth and predictions of animal productivity varied widely among the species challenged with drought and defoliation stresses. Predicted liveweight gains of weaner sheep under severe drought conditions (10-P) varied between species ranging from 20 to 110 g/day. Under the same conditions, predicted wool growth rates varied between species from 5 to 11 g/wether. day, while pasture growth rates varied from a low of 0 to more than 120 kg DM/ha. day. The animal effects were due largely to differences in herbage mass and the degree to which the grass remained green. These results highlight the importance of maintaining the most productive species in pastures through drought.
White clover (Trifolium ripens L.) herbage production in intensively grazed pasture is related to clover stolon growing point density. High stolon density is associated with small leaf size. The objective of this study was to examine the probability of breaking the genetically controlled link between leaf size and stolon density by manipulating internode length and branching propensity. Two white clover cultivars, Grasslands Tahora and Grasslands Kopu, were grown in two New Zealand environments, full sunlight or 50% sunlight (shade), during 1991 and 1992. Selections were made for high or low frequency of stolon branching, long or short stolon internodes, and large or small leaves. These selections were polycrossed within groups to give 24 lines. Lines were evaluated in pots grown outside to determine the effect of selection on these and other shoot characters. Selection of populations with high or low frequency of branching gave progeny with different frequency of branching for all cultivar-environment combinations except for selection within Tahora grown in shade. Selection of populations with long or short internode length gave progeny with different internode length in all cultivar-environment combinations. Selection for large and small leaflet width gave progeny with different leaflet width in all cultivar-environment combinations except for selection within Kopu grown in sun. Two estimates were made of narrow sense heritabilities. Estimates from mid-parent versus progeny regression heritabilities were higher for internode length and leaflet width than for frequency of branching. Realized heritabilities were again generally higher for internode length and leaflet width than for frequency of branching although there were some exceptions. Selection for high frequency of branching in Tahora grown in full sunlight had a high realized heritability. Stolon characters, such as internode length and frequency of branching, can be effectively manipulated by selection. The degree of selection success can be affected by environment and cultivar. Selection for variation in internode length is likely to be more successful than for frequency of branching.
Steers were fed for nine weeks on either ryegrass/clover pasture or maize (six animals per group), to evaluate the effects of diet on attributes of meat and fat. Feed intake was restricted in the grain‐fed group with the intention of producing equivalent growth rates in the two treatment groups, but this resulted in significantly slower weight gain, reduced carcass weight, and reduced subcutaneous and intramuscular fat. Nevertheless, the glycolytic potential (an estimate of pre‐slaughter glycogen) in the M. longissimus dorsi lumborum was approximately 20% higher (P < 0.05) in the grain‐fed cattle, while the ultimate pH of the meat was equivalent for both groups. The results suggest that grain‐based diets can increase muscle glycogen concentrations independent of the higher calorific intake normally associated with grain diets, probably in response to changes in rumen fatty acid production. Compared with grain diet, pasture diet resulted in significantly higher (P < 0.01) muscle tocopherol content, but did not influence meat colour. The dietary treatments influenced fat colour, but both carotene content and energy intake may be responsible for this effect. The microbiological profile of meat during chilled storage was not affected by diet.
Merino wethers were grazed continuously on a predominantly annual pasture in the Mediterranean environment of South Australia to assess the animal and pasture responses to, and financial returns from, factorial combinations of stocking rate and superphosphate. Stocking rate and superphosphate both significantly influenced pasture production, pasture availability, percentage pasture utilization and consequent sheep body weight, wool production, and wool value. Neither main effect markedly influenced botanical composition. Significant interactions between stocking rate and superphosphate occurred in relation to sheep body weight on some occasions during the third year of the experiment, and in the case of wool per head, wool per acre, and value of wool per acre in the second and third years of the experiment. The results showed clearly that there was no economic justification for applying high levels of superphosphate to old pasture land unless the additional pasture production was utilized through an increased stocking rate. Only at the high stocking rate was there a significant correlation between pasture production and wool production. At this high stocking rate there was marked dependence on medium or high rates of application of superphosphate to ensure satisfactory levels of pasture production, pasture availability, wool production, sheep survival, and profitability.
In a 4-year grazing experiment with Merino sheep, on a native pasture dominated by Bothriochloa ambigua S.T. Blake, three rates of stocking and continuous v. rotational grazing were compared. The effects of these treatments on the forage available and the botanical composition of the pasture and on sheep liveweights, size of sheep, wool production, wool fibre diameter, and parasitic infestation, both with and without drenching with phenothiazine, mere studied. The effects of seasonal conditions on the above and on the chemical composition of the pasture were also recorded. No consistently significant differences between grazing treatments in their effects on the pasture or on sheep liveweights or parasitic infestation were recorded, although during the final 3 years the total forage available was less under heavy stocking. Seasonal variations in total forage mere not marked, but, production of green forage increased greatly in the spring and declined to a very low level during winter. Similarly, sheep liveweights increased during spring and summer and declined in the winter. These liveweight changes were significantly correlated with the amount of green forage available. Wool fibre diameter showed similar seasonal fluctuations but the maximum diameter was attained earlier than maximum liveweight. Coincident with a spring rise in the amount of green forage there was also an increase in the percentages of crude protein and phosphorus in the green components of the pasture. Liveweight gains of the drenched sheep were significantly greater from the beginning of each experimental year in the late spring (November) to late winter (August) in all stocking treatments. In the spring, when the quality of the pasture improved and worm egg counts were low, drenching had no effect on liveweight gains in three out of four years. Drenching also significantly improved wool production and resulted in an increase in skeletal size of sheep in three out of four years. Drenching reduced egg counts of the parasites Oesophagostomum spp. and Haemonchus contortus (Rudolphi) Cobb but was less effective against Trichostrongylus-Ostertagia spp. For all grazing treatments there was no significant difference in the amount of wool produced per head, but over the 4-year period 56 per cent. more wool per acre was produced from the heavy than from the light rate of stocking.
Two lines of perennial ryegrass (Lolium perenne L.), cv. Aurora and breeding line Ba 11351, from the United Kingdom with elevated concentrations of water-soluble carbohydrates in the shoot were compared with the standard cultivars, Ellett, Vedette and Kangaroo Valley, in pure grass swards under irrigation at Kyabram, Victoria, and Gatton, Queensland, and under natural rainfall at Condah, Victoria, during 1995–97. Near infrared reflectance spectroscopy was used to predict the water-soluble carbohydrate, crude protein, in vitro dry matter digestibility, neutral and acid detergent fibre, and Klason lignin concentrations of the perennial ryegrass herbage. Herbage yield and water-soluble carbohydrate differed between cultivars at each site at most harvests, with the high water-soluble carbohydrate lines usually yielding less and having higher water-soluble carbohydrate concentrations than the 3 standard cultivars. However, the high water-soluble carbohydrate lines also had higher water-soluble carbohydrate concentrations at harvests where their yield was equal to the standard cultivars. The other nutritive value traits differed significantly at more than half of the 32 harvests: the high water-soluble carbohydrate lines had higher crude protein and dry matter digestibility, and lower neutral detergent fibre, the neutral detergent fibre containing less acid detergent fibre and lignin than did the standard cultivars. The high water-soluble carbohydrate lines were more susceptible to crown rust during spring and summer than the standard cultivars at Kyabram and Gatton: heavy infections reduced yield, water-soluble carbohydrate, dry matter digestibility and crude protein. Higher water-soluble carbohydrate may depend on only a few genes, as does rust resistance and it seems likely that high yielding, high water-soluble carbohydrate cultivars can be developed by recombination and selection.
A study was made over 2 years of the nutritive value of the subterranean clover (Trifolium subterraneum L.) cultivars, Trikkala, Larisa and Goulburn, in grazing experiments with Border Leicester x Merino lambs. Liveweight gain was similar for all cultivars in the first year and in the second year was higher on Larisa (153 g/day) compared with Goulburn and Trikkala (131 and 103 g/day, respectively). Wool growth was not significantly different between cultivars. Both the digestibility and water-soluble carbohydrate content of the petiole and stem plant fraction were significantly (P<0.05) higher than those of the leaf fraction, even though the leaf had a lower level of cell wall organic matter. The ratio of lignin to cell wall organic matter was also higher in the leaf fraction. Samples obtained via oesophageal fistula showed that petioles comprised most of the dry matter in the diet and, thus, were the major contributor to energy supply. Differences were found in the degradability characteristics of the 3 cultivars which led to significant (P<0.05) differences in the concentration of rumen degradable dry matter and effective rumen degradable protein (ERDP). During the vegetative and early flowering stages, the concentration of ERDP exceeded the supply of fermentable metabolisable energy required for microbial protein synthesis. In mature clover, the concentration of ERDP was low and limiting microbial protein synthesis. The degradation characteristics of protein were highly correlated with liveweight gain (r2 = 0.90) and wool growth (r2 = 0.70). It is suggested that increasing the petiole : leaf ratio could increase the efficiency of utilisation of subterranean clover diets.
THE functioning and sustainability of ecosystems may depend on their
biological diversity1-8. Elton's9 hypothesis that
more diverse ecosystems are more stable has received much
attention1,3,6,7,10-14, but Darwin's proposal6,15
that more diverse plant communities are more productive, and the related
conjectures4,5,16,17 that they have lower nutrient losses and
more sustainable soils, are less well studied4-6,8,17,18.
Here we use a well-replicated field experiment, in which species
diversity was directly controlled, to show that ecosystem productivity
in 147 grassland plots increased significantly with plant biodiversity.
Moreover, the main limiting nutrient, soil mineral nitrogen, was
utilized more completely when there was a greater diversity of species,
leading to lower leaching loss of nitrogen from these ecosystems.
Similarly, in nearby native grassland, plant productivity and soil
nitrogen utilization increased with increasing plant species richness.
This supports the diversity-productivity and diversity-sustainability
hypotheses. Our results demonstrate that the loss of species threatens
ecosystem functioning and sustainability.
This paper reports on the growth periodicity of introduced temperate perennial pastures in a summer-rainfall environment in the high-rainfall zone of eastern Australia. Data were derived from an experiment (1985-87) directed at evaluating pasture cultivars when sown in binary mixtures grazed by sheep. The data were also simulated by using the decision support system SheepO (Version 4·0) and validated by visual techniques, deviance measures, and statistical tests. The model simulated pasture growth rate and total biomass with acceptable accuracy. The study provided a quantification of the growth rhythm of temperate perennial pastures in this environment. The data show that growth rhythm comprises a high growth rate (>50 kg DM/ha·day) during the primary growth cycle in spring, a moderate growth rate (20-50 kg DM/ha·day) during the secondary growth cycle in summer-autumn, and low growth rate (<20 kg DM/ha·day) in winter. The growth performance of introduced pastures based on cv. Demeter tall fescue (Festuca arundinacea) exceeded that of pastures based on cv. Sirosa phalaris (Pharlaris aquatica) in all seasons, at low and high stocking rates, and in all 3 years. The results highlight the potential for pasture cultivars with enhanced seasonal growth rate to increase the pasture feed supply for grazing animals.
The feeding values of subterranean clover, lucerne, phalaris and Wimmera ryegrass were measured in three experiments using weaned lambs. With dried herbage, the voluntary intake of each species increased linearly with organic matter digestibility over the range tested (57-83%). Regressions for the two grasses did not differ from each other, nor did those for the two legumes; a common regression for the legumes had the same slope as that for the grasses but dry matter intake was about 190 g/d greater on legume diets. Digestibility accounted for 50 and 68% of variation in intake of legumes and grasses, respectively, but when cellulose concentration in the diet was used as the predictor, a single regression satisfied all the data and accounted for 76% of variation in intake. Energy retention by weaned lambs offered diets of dried subterranean clover or lucerne was 53% greater than that by lambs receiving the same intake of metabolizable energy from phalaris. When the intake of the two legume diets was unrestricted, this difference increased to 128%. Despite the 30% higher voluntary intake of the legume diets, the weight of digesta in the reticula-rumen at the end of a meal was the same as it was for the phalaris diet. When all four species were compared in the field, with herbage amply available, lambs grazing the two legumes retained 57% more energy than those on the grasses during the main spring period when the species were of comparable digestibility. As there was little or no difference, under the conditions of this experiment, in the intake of food from the four swards, it is concluded that the difference in feeding value resulted from more efficient use of metabolizable energy. Overall, subterranean clover had as high a feeding value for lambs as lucerne, and phalaris was not inferior to Wimmera ryegrass.
White clover was introduced to Australia with the early European settlers in the late 18th century and is now the most valuable pasture legume in high rainfall temperate regions of Australia. Through a process of ingress and naturalising in conjunction with pastoral expansion during the 19th century and widespread pasture improvement in the 20th century, white clover now occupies 6 million hectares in Australia and is of major significance for the sheep, beef cattle and dairy industries. This paper describes these historical influences on formation of the white clover zone in Australia and the continuing requirement for better adapted cultivars in key agro-geographic regions, with particular close reference to the northern tablelands of New South Wales—the most extensive dryland region. These considerations provide a basis for defining breeding objectives for white clover improvement in Australia.
Medium Peppin Merino wethers were fed, ad libitum, subterranean clover (cv. Woogenellup), rose clover (cv. Kondinin) and soft brome grass cut in September (spring), November (late spring) and January-February (summer). The nitrogen contents of the subterranean clover ranged from 1.89 to 3.13%, of the rose clover from 1.62 to 2.84% and of the soft brome from 0.42 to 2.86%. Mean daily organic matter intakes (kg) in spring, late spring and summer were respectively: for subterranean clover 0.78, 1.09 and 0.42; for rose clover 0.60, 0.87 and 0.62; for soft brome grass 0.87, 0.81 and 0.20. Organic matter digestibilities in spring, late spring and summer were, respectively: for subterranean clover 0.82 ,0.69 and 0.61; for rose lover 0.80, 0.62 and 0.54; for soft brome 0.83, 0.72 and 0.58. There were highly significant differences ( P < 0.001) in nitrogen balance between seasons. The estimated digestible energy intakes (MJ/day) in spring, late spring and summer were, respectively: for subterranean clover 12.7, 14.5 and 4.9; for rose clover, 9.2, 9.9 and 6.9; for soft brome, 13.6, 10.1 and 2.1. Within seasons there were significant (P < 0.05) differences in nitrogen balance between species. There were significant differences between species in mean retention time in the alimentary tract in late spring (P<0.001) and summer (P<0.001) but not in spring. There was a highly significant negative relationship between acid-detergent fibre content and both organic matter and fibre digestibilities. The superior digestible energy intakes of the 2 clovers explain at least some of the superior performance of sheep grazing clover compared with those grazing grass pastures.
An experiment was conducted to examine the effect of deep-rooted perennial grasses on the water and nitrogen economy of 3 mature pasture communities with different botanical compositions but the same fertiliser history. One pasture was dominated by volunteer naturalised pasture grasses (Eleusine tristachya and Danthonia spp.) (termed ‘degraded’), another was phalaris (Phalaris aquatica) dominant (phalaris), and a third was dominated by phalaris into which white clover (Trifolium repens) had been recently sown (phalaris–white clover).
Two replicates of each pasture type were grazed continuously over 4 years with young weaner sheep changed each year. Measurements of hydrology, nutrient cycling, botanical composition and animal production were made in order to quantify the sustainability characteristics of each of the pasture types.
Data are summarised as absolute measures at various points in time and also as trends over time. The ranking of standardised treatment measures was then summed to provide an index of sustainability with or without a weighting assumed to be representative of the relative importance of various layers of sustainability viewed from the perspective of a hypothetical ‘typical’ grazier. The results show that the phalaris–white clover treatment was substantially more sustainable, in both ecological and economic terms, than either of the other treatments. The unweighted index for the phalaris–white clover pasture was 3.61 compared to 2.08 and 1.98 for the phalaris and ‘degraded’ pastures, respectively.
Practical application of simulation modelling as a decision aid for grazing system management usually involves an assumption of uniformity of model inputs over a farm paddock or property. In reality, paddocks and farms display high spatial variability in model inputs. There is considerable interest in assessing the significance of this spatial variablity for anmal production and enterprise profitability. This study seeks to demonstrate the use of spatial data with the GRAZPLAN pasture model to provide estimates of annual net primary production from pastures at a farm scale on the Northern Tablelands of New South Wales, Australia. The GRAZPLAN pasture model was validated against data from 2 separate field experiments for a typical improved pasture based on Phalaris aquatica from 1968 to 1972. A spatial coverage, classifying paddocks into 9 pasture types based on a botanical survey, was used to define the pasture parameter sets used in simulations. A Landsat TM satellite image classified to give 3 pasture growth status classes was used to define within-paddock levels of a fertility index used in the simulation model. Simulations over 1975–94 were conducted for all combinations of pasture types and fertility scalar values using climate data for the CSIRO Pastoral Research Laboratory near Armidale. Simulation output was written to a lookup table and imported into a PC-based geographic information system. The spatial data layers were combined to form a display template representing spatial variation in pasture type, pasture condition and fertility. The spatial template was reclassified using the lookup tables to create maps of annual net primary production from pastures. Spatial variability in simulated annual net primary production was greater for the paddocks with diverse mixtures of sown and native species than for the more uniform highly improved or pure native pastures. The difference in response to rainfall of simulated net primary production was greater between different pastures types than between different levels of the fertility index. The resulting maps provide a demonstration of the way in which satellite imagery and other data can be interfaced with a decision support system to provide information for use in precision management of grazing systems. Implementation of such methods as a management tool will depend on development of quantitative spatial data layers which provide accurate and repeatable initial conditions and parameter values for simulation models.
As the effectiveness of current anthelmintic drenches is being reduced by the emergence of drench resistance and significant production losses may still occur as a result of continuing larval challenge, strategies for nematode control should focus on preventing the build-up of infective larvae on pasture rather than treating the infection. This paper reports the effects of condensed tannins (CT) extracted from Lotus pedunculatus, Lotus corniculatus, sulla (Hedysarum coronarium) and sainfoin (Onobrychus viciifolia) on in vitro viability of eggs, first stage larvae (L1) and third stage larvae (L3) of the sheep nematode, Trichostrongylus colubriformis. When in vitro assays contained CT in a similar concentra-tions to that in the digestive tract of sheep fed these forages, the CT reduced the development of eggs to L3 larvae as well as the proportion of eggs hatching. The CT also reduced the development of L1 larvae to L3 larvae and decreased the motility of L3 larvae when assessed by the larval migration inhibition assay and this may reduce their infective capacity in vivo. If these forages are fed to grazing sheep, then it may be possible to reduce contamination of pasture with infective larvae and reduce our dependence on anthelmintics as the principal method for controlling internal parasites.
Izmir is a hardseeded, early flowering, subterranean clover of var. subterraneum (Katz. et Morley) Zohary and Heller collected from Turkey and developed by the collaborating organisations of the National Annual Pasture Legume Improvement Program. It is a more hardseeded replacement for Nungarin and best suited to well-drained, moderately acidic soils in areas with a growing season of less than 4.5 months. Izmir seed production and regeneration densities in 3-year pasture phases were similar to Nungarin in 21 trials across southern Australia, but markedly greater in years following a crop or no seed set. Over all measurements, Izmir produced 10% more winter herbage and 7% more spring herbage than Nungarin. Its greater hardseededness and good seed production, makes it better suited to cropping rotations than Nungarin. Softening of Izmir hard seeds occurs later in the summer–autumn period than Nungarin, giving it slightly greater protection from seed losses following false breaks to the season. Izmir is recommended for sowing in Western Australia, New South Wales, Victoria, South Australia and Queensland. Izmir has been granted Plant Breeders Rights in Australia.
Ryegrass pastures in New Zealand are usually infected with the ryegrass endophyte (Neotyphodium lolii). The endophyte provides protection from invertebrate attack, discourages overgrazing by livestock and perhaps confers other advantages enhancing ryegrass persistence. The endophyte lifecycle is completed within the plant, and transmission is uniquely through the grass seed. Within the plant, the endophyte synthesises a range of compounds, some of which have been identified as responsible for known endophyte effects on pasture invertebrates and on livestock. The concentrations of these compounds vary in different parts of the plant, with plant age and in response to environmental influences. While endophyte has wellknown adverse effects on livestock (reviewed elsewhere in this volume), it contributes positively to grassland productivity in New Zealand. Keywords: endophyte, Lolium, Neotyphodium lolii, pest resistance, ryegrass
"Sustainability" is a social construct, and is difficult to define in precise value-free terms. It has ecological (biophysical) and socio-economic dimensions. Biophysical indicators are tools that can be used to define resource status. They cannot directly measure sustainability, but are useful for comparing present resource status with defined limits set within a socio-economic framework. We measured vegetation and soil variables in 4 areas of grazed North Island hill country with different management (fertiliser application/stocking rate) histories (1973 to 1994) and sub-divided into 36 paddocks. Nineteen vegetation (including herbage production); soil chemical, physical and biological; and soil water variables were selected as potentially useful biophysical indicators. Analysis of the results for these variables suggested that pasture botanical composition (especially content of high-fertility responsive grasses and of herbaceous weed species) and earthworm mass/unit area explained most of the variance of the data matrix. These variables were also highly correlated with herbage production, an indicator of likely economic performance. Development of the most suitable indicators requires good understanding of agro-ecosystem function, and is hampered by our lack of understanding of critical processes. Keywords: biophysical indicators, hill country, pasture, soil, sustainability
Groups of two young steers and eight autumn lambing ewes, mated for prime lamb production and each rearing a single lamb, grazed together at three stocking rates and separately each at five stocking rates on annual pasture. Results were rejected for animals fed a supplement. In most instances when pasture conditions were fairly good throughout the year, mixed stocking increased production. In one year when pasture was very poor during winter, mixed stocking resulted in little or no increase in production. The weight changes of the animals suggest that most of the benefit from mixed stocking occurred during winter. The effect of mixed stocking on production varied with stocking rate only in the first pear. In general, the competition between sheep and cattle, as measured by annual production, did not vary with stocking rate. The sheep appeared to benefit more than the steers from mixed stocking, but this may have been a consequence of the stocking ratio selected.
Ryegrass/endophyte associations have been developed which produce peramine, but not the endophyte toxins ergovaline or lolitrem B. Sheep grazing these ryegrasses in small paddocks and in a systems trial over three years gained weight as rapidly as those grazing endophyte-free ryegrass, and showed none of the adverse responses associated with grazing ryegrass naturally infected with wild-type endophyte (Neotyphodium lolii). Growth rates, rectal temperatures, respiration rates, serum prolactin concentrations, ryegrass staggers scores and scores for dag burdens were equivalent for the selected endophyte and nil endophyte treatments, whereas sheep grazing the wild-type endophyte treatment were adversely affected for all parameters. This was reflected in calculated gross margins for the systems trial of only 700 per hectare for each of the other treatments. To date there have been no conclusive studies of non-toxic endophyte with cattle. Keywords: AR1, dags, endophyte, ergovaline, liveweight gain, lolitrem B, Lolium perenne, Neotyphodium, peramine, perennial ryegrass, prolactin, sheep
Although pastoral finishing systems are inexpensive, they result in some quality outcomes that set meat from such animals apart from the grain-finished equivalent. These outcomes, including meat and fat color, fat composition, meat pH, and odor/flavor profiles, have a chemical basis that can be traced to pastoral production. The color of raw meat is indirectly linked to pasture composition in several ways. Meat color stability, i.e., maintenance of oxymyoglobin (bright-red) rather than its auto-oxidation to metmyoglobin (brown), is helped by dietary antioxidants, like tocopherol. Tocopherol is abundant in green pasture but not grain. The pigment carotene, another antioxidant also abundant in pasture, is the cause of variably yellow fat in pasture-finished cattle. Although ruminants tend to hydrogenate unsaturated fatty acids present in the diet, some fatty acids escape this fate and are incorporated directly in storage triglycerides. As a result, the melting points of storage fats can differ due to diet, as can the pattern of fat oxidation during cooking. The latter results in different odor/flavor profiles, which may be partly responsible for ‘pastoral’ flavor. Flavor profiles also differ with meat pH, which in turn has links to diet and production systems. Work with sheep suggests that the fecal-smelling compound skatole (3-methylindole) is often generated by the excess protein in pastoral diets. Skatole can accumulate in storage fats, and may be a major contributor to pastoral flavor. These and other meat quality issues and their chemical links to production and diet are examined in this review
The effect of varying price ratios between liveweight and supplementary feed on the optimum stocking rate (SR) of a beef herd on range is analyzed in relation to the net value of weaned calf live weight. While the basis for determining optimum stocking rate is generally the value of production and costs per unit area, the animal performance per se is often a major management criterion, especially where the capital investment in livestock is high and where risk avoidance is an important consideration. Consequently, equations expressing the net value of beef production per unit of land and per animal unit are formulated as a function of SR. Parameter values for the equations were taken from a grazing trial conducted in the Galilee in Israel where a beef herd was maintained yearlong on native range 5 years at 3 different SR's, 0.50, 0.67, and 0.83 cows/ha. The animals were supplemented ad libitum with poultry litter during the dry summer months. During the transitional period between the opening rains and range readiness, poultry litter was enriched with 20% barley grain. In addition, straw was given at an average rate of 80 to 375 kg/ha in the intermediate and highest stocking rates. Over the range of SR's studied, it was shown that when supplementary feed and other per animal costs are high, net value of production per unit area of range declines with SR even though total production increases. On the other hand, when fixed range and management costs are high, the net economic benefit per cow increases with SR even though production per cow decreases. It is concluded that the optimum SR for a given situation depends not only on the input/out price ratios but also on the criterion for evaluating economic value that is most revelant to the manager.
Temperate forage legumes that contain condensed tannins (CT) have been evaluated under experi-mental conditions and some have demonstrated significant benefits for sheep, cattle and deer. Condensed tannins can significantly improve productive performance, as well as lessen our dependence on anthelmintic drenches. However, not all CT are equal and some may not benefit production at all. This paper summarises the performance responses of ruminants to CT in birdsfoot trefoil (Lotus corniculatus), lotus (Lotus pedunculatus), sulla (Hedysarum coronarium), sainfoin (Onobrychis viciifolia) and erect dorycnium (Dorycnium rectum), and indicates the requirements for successful establishment and management of these swards. All require specialist care, and few will compete with common pasture species in high-fertility situations, but the potential benefits of reduced anthelmintic requirements when sheep are fed sulla, and the lowered incidence of flystrike and improved weight gain, wool growth, milk production and ovulation rate attributable to the CT in birdsfoot trefoil, makes these attractive options for farmers. Lotus is a high quality feed for wet, acid, low-fertility soils and sainfoin may result in very good stock performance in dry regions. Annual dry matter yields of the five species outlined here range from about 10 to 25 t/ha and some of these forages will benefit producers who are prepared to manage these forages correctly.
The grazing value of phalaris–white clover and tall fescue–white
clover pastures was compared in a temperate summer-rainfall environment in the
high rainfall zone of eastern Australia. Data were derived from an experiment
which evaluated pasture cultivars when grown in binary mixtures and grazed by
sheep. The data were also simulated with the decision support system SheepO
(Version 4.0) and validated by visual techniques, deviance measures, and
statistical tests. The model generally simulated green biomass, liveweight
gain, and clean fleece weight with acceptable accuracy. Pasture based on tall
fescue–white clover produced more green pasture biomass in all seasons,
in all years, and at both low (10 sheep/ha) and high (15 sheep/ha)
stocking rates when compared with phalaris–white clover. Sheep grazing
tall fescue–white clover pasture were turned off about 5 kg heavier each
year and produced about 0.6 kg/head more clean fleece weight; the wool
production per head of sheep grazing tall fescue–white clover at 15
sheep/ha was similar to that for sheep grazing phalaris–white clover
pasture at 10 sheep/ha. These differences in wool production were
accompanied by consistent effects on wool quality; the fleeces of sheep
grazing tall fescue–white clover pasture were markedly sounder in
tensile strength but broader in fibre diameter. These data and the SheepO
simulations highlight the potential for pasture cultivars with enhanced
seasonal growth and nutritive value to alleviate feed-gaps and improve the
feed-base for grazing animals.
The study of the relationship between species richness of a plant
community and its productivity has received much attention, recently
renewed by the concern on the loss of biological diversity at a global
scale. Here, we briefly review some indices widely used in agronomic and
competition experiments to compare monocultures and mixtures, and
compare them to other, more recently designed ones. These various
indices are then calculated for two experiments. In the first
experiment, two grass and two legume species were grown at six levels of
nitrogen availability, either in monocultures or in mixtures of the four
species in a substitutive design; in the second experiment, five grass
species were grown at 16 levels of total nutrient availability, either
in monocultures or in mixtures of the five species in an additive
design. These data clearly show that the conclusions drawn from the
experiments depend on the index used to compare the experimental
communities. We argue that a clear test of whether the productivity of
communities increases with species richness requires that: (1) all
species present in the multispecies assemblages also be grown in
monocultures under the same environmental conditions, and (2) the
productivity of these assemblages be compared to the most productive
monoculture. We conclude that there are as yet very few cases where
superior productivity of multispecies assemblages as compared to
monocultures has been clearly shown.
Since the early 1970s the Bureau of Land Management (BLM) and the Forest Service have emphasized the monitoring approach in managing their rangelands. After a 5-year period of intensive monitoring, stocking rate and other management actions are typically adjusted, depending on whether a definite downward or upward trend in range condition is observed. Examining the Afton Allotment on BLM land in southcentral New Mexico, we demonstrate serious flaws in the monitoring approach and other BLM grazing policies. Monitoring reflects past management but does not consider the future. Perverse incentives for permittees to maximize permit value rather than sustain the forage base still remain in place. The "Range Reform '94" proposals by the U.S. Department of the Interior do not address these incentives and other flaws in public land policy. We would reform federal grazing land policy by coupling grazing fees to grazing intensity. Ranchers choosing conservative sustainable grazing intensities would pay low fees, whereas those choosing heavy grazing intensities would be charged higher rates. We would also implement other reforms: making livestock grazing permits transferable to other uses, discontinuing subsidies, eliminating restrictions on nonuse, offering incentives for public land investment, and establishing a biodiversity fund.
Leaf shear strength of perennial ryegrass (Lolium perenne L.) was studied as a possible indicator of the resistance of herbage to breakdown during chewing and rumination. Leaf strength as measured on a Warner-Bratzler meat tenderometer proved to be readily recorded, repeatable, and heritable. Predicted heritability within a synthetic cultivar was calculated as 0.36.
The concentrations of phenol and indole flavour compounds in the fat of beef cattle finished for nine weeks on either ryegrass/clover pasture or a maize‐based grain diet were determined, and compared with urinary concentrations of phenols (both free and total) and with dietary parameters including phenolic acids. The concentration of skatole in the fat was significantly higher for the pasture‐fed steers. Treatment effects on phenol concentrations in the fat were not significant for most phenols, although phenolic intake and, in most cases, urinary excretion was higher on the pasture diet. 4‐Ethylphenol was a distinctive marker of the maize‐based finishing diet in both urine and fat.
The oestrogenic activity of three varieties of subterranean clover (Trifolium subterraneum L.) — Dwalganup, Yarloop, and Mount Barker — was measured by means of the response in fresh weight of uterus + cervix in both ovariectomized virgin and ovariectomized cast-for-age ewes. The standard oestrogen used was diethylstilboestrol, administered intramuscularly. There was no difference between virgin and aged sheep in the slope of the dose-response curve. Thus aged sheep can be used for biological assay of oestrogens. The varieties Yarloop and Dwalganup were highly potent; Mount Barker produced only slight increases in uterine weight. The relevance of these varietal differences in oestrogenic potency is discussed in relation to the sheep infertility problem associated with oestrogenic pastures.
Milk production for the first 10 weeks was measured in Merino ewes grazed over a 3-year period on native and sown pastures at different stocking rates and under two systems of management; the growth of their lambs was also measured. It did not appear that milk production by the Merino ewe was a limiting factor In growth of single lambs. Lactation curves for the Australian Merino are different from those published for British breeds of sheep. Higher milk production was recorded in ewes: (a) rearing twin lambs as compared with single lambs; (b) rearing single crossbred lambs as compared with single Merino lambs.
Optimal economic policies with respect to stocking rate and season of grazing for an arid chenopod pasture type were derived for various starting states under a stochastic optimal control framework. Optimal policies were determined using decision criteria which involved either no discounting of future returns or a discount rate of 6%, and were further evaluated by analysing their long-run economic and ecological consequences. All optimal policies involved either year-long set stocking or destocking. Policies involving seasonal grazing or variable stocking rates were not economically viable at the specified cost levels. Optimal stocking rates increase with the level of forage biomass and the density of adult plants, but decrease with the level of either young or old seedlings when these provide an opportunity for regeneration of degraded range. Without discounting, pastoral use of this vegetation type can be both economically and ecologically sustainable. Long-run vegetation dynamics under this criterion are similar to those expected in an ungrazed community. However, land which is severely degraded is, for all practical purposes, not recoverable either by privately optimal grazing management or by complete removal of grazing. Discounting of future returns results in a more exploitative set of grazing policies and reduces opportunities for regeneration of degraded land. Pastoralism under this criterion is not ecologically sustainable although it is economically viable. The role of such analyses in pastoral management decision-making, and the implications of the results for policy with respect to administration of public rangelands, are briefly discussed.
White clover genotypes selected for frost tolerance and susceptibility were pair-crossed in various combinations with unselected genotypes of Grasslands Huia. Progeny lines and parent genotypes were artificially frosted at −8°C and scored for percentage of leaves damaged. Progeny from crosses between frost-tolerant genotypes were less damaged by frost than progeny from crosses involving either susceptible genotypes or unselected Grasslands Huia genotypes. Heritability estimates for frost tolerance or susceptibility were high, ranging from 0·75 to 0·93, depending on method of calculation. Removal of leaf-size effects from scores of frost damage reduced heritability estimates to 0·54–0·73. It was concluded that, because heritability for frost tolerance was high, selection for this character and incorporation of frost tolerance into agronomically suitable but frost-sensitive cultivars by breeding would be successful.
A series of experiments was conducted at Palmerston North, New Zealand, during 1988–91 to compare the efficiency of chewing during eating and rumination, rumen fractional outflow rate (FOR), voluntary organic matter intake, liveweight gain and wool production in sheep fed either low (LS) or high (HS) leaf shear breaking load perennial ryegrass (PRG). The LS ryegrass had a 13% lower mean leaf shear breaking load and ingestion rates tended to be higher than for HS PRG, but no consistent significant treatment differences were observed in rate of particle breakdown, rumen FOR, voluntary intake or animal performance. It was concluded that selection for reduced leaf shear breaking load per se did not improve feeding value. The total shear load required to reduce a unit dry weight of PRG leaf to < 1 mm particles (index of masticatory load; IML) differed by only 3% between LS and HS PRG in this study, due to higher leaf length:dry weight ratios for LS PRG. It is therefore suggested that IML, which takes into account both leaf shear breaking load and associated changes in leaf morphology may be a better criterion for selection than leaf shear breaking load alone in breeding programmes to improve the feeding value of perennial ryegrass.
White clover genotypes were selected for high and low values of leaf size, taproot diamater, number of taproots, proportion of total root and taproot dry weight. Crosses within selected groups of genotypes resulted in 14 seed lines, which were compared with parent genotypes in field tiles. Selections for taproot diameter and proportion taproot were more successful than those for taproot number and proportion root.
Narrow sense heritability of characters calculated by regression of progeny on mid-parent values were well correlated with broad sense heritabilities derived from replicated clonal comparisons (r=0.73*), indicating that the genetic variation is controlled predominantly by additive gene effects.
Molybdenum in relation to pasture improvement in South Australia
- A J Anderson
Anderson, A. J. 1946. Molybdenum in relation to pasture
improvement in South Australia. J.C.S.I.R. 19:1-13.