Literatura científica selecionada sobre o tema "Grass tetany (Australia)"

Grass tetany is a common metabolic disorder of ruminants in southern Australia. To investigate the genetic control of mineral concentrations leading to this disorder, replicate populations of perennial ryegrass half-sib families were grown at Hamilton and Timboon in southern Australia. Variation in herbage yield, and Mg, P, K, Ca, Na, Cl, S, Mn, Fe, Cu, Zn, and K/(Mg+Ca) (tetany ratio) concentrations in the herbage of these families was measured in the early spring of 1994. Large environmental effects on herbage mineral concentration were detected, with location differences accounting for 60–80% of the total variance. Both the mean and range for mineral concentration were similar for each population. As expected, Mg, Ca, and K were significantly correlated with tetany ratio; however, the concentrations of other minerals were not consistently associated with tetany ratio. Tetany ratio and Mg showed a negative genetic correlation in both groups. The genetic correlation for tetany ratio with K or Ca was less repeatable across groups. Significant family variance components (σ2f) were detected for yield, Mg, Ca, K, and tetany ratio, and narrow-sense heritabilities for these traits were moderate to high (h2 = 0·46–0·81). However, family location interactions were also significant, with σ2fl often >σ2f. A large proportion of the family location interaction for K and Mg concentration was associated with non-rank family changes indicating that family selection for low K or high Mg concentration would be effective across environments. However, family × location effects for Ca and tetany ratio were associated with substantial rank changes across locations. Selection for increased Mg concentration would appear the most suitable strategy for reducing the tetany ratio of perennial ryegrass, with possibly different cultivars required for the environments represented by Hamilton and Timboon.

The occurrence of grass tetany related deaths in cattle grazing pasture in the South East of South Australia is related to soil type. The greatest losses occur on the solodised solonetz soils, with few, if any, on the rendzina or siliceous sand soils in the region. Pastures from 3 soil types were sampled on 2 occasions during the growing period, and soils were sampled once. Comparisons were made for the pasture components of potassium (K), calcium (Ca) and magnesium (Mg) concentrations in soils, and K, Ca, Mg, nitrogen (N) and sulfur (S) concentrations in plants. In the July sampling, the mean herbage K/(Ca + Mg) ratio for both annual and perennial grass species grown on the solodised solonetz soils exceeded 2.2 but was below 2 for the other 2 soil types. At the same time the mean K/(Ca + Mg) ratio for soil-extractable cations was 0.10 for the solodised solonetz soils but only 0.058 and 0.025 for the rendzina and siliceous sand soils. A critical value for the K/(Ca + Mg) ratio for the soil extractable cations of 0.07-0.08 is suggested. Of the 22 sites in the investigation, grass tetany deaths had occurred on 9 within the previous 5 years; all of these were classified as solodised solonetz soils. Deaths were reported in late autumn and winter, and in all cases the dominant pasture species growing at these sites in July were grasses. It is suggested that deaths ceased in spring because there was either a change to legume dominance or an increase in air temperature.

Integration of crops and livestock has been revitalised in Australia, initially as an opportunity to increase cropping within the high-rainfall grazing zones, and more recently, to improve enterprise diversification and profitability across the low-, medium- and high-rainfall, and mixed-farming zones. Young crops are highly digestible (>80% dry matter digestibility, DMD) with a high energy density (>12 MJ/kg DM) and, in much of southern Australia, fill a winter feed gap. The quality and time of feed availability also coincide with the high nutrient requirements of ewes in late pregnancy and lactation. In Western Australia and South Australia, young crops are available for lactating ewes and young growing lambs (autumn lambing). For the smaller proportion of growers who lamb later in winter, young crops are available for the last 1–2 months of pregnancy. In the later-lambing states of New South Wales and Victoria, crops may be grazed by ewes at any stage of pregnancy and lactation and/or by young lambs. In Tasmania, crops are more likely to be available during early–mid-gestation. Limited studies on feed budgeting with grazing crops have indicated that ewes can maintain or even increase liveweight, with a much lower level of feed on offer than would be required with traditional pastures (<500 kg DM/ha). This has the potential to increase whole-farm stocking rates and/or reduce fetal mortality, increase lamb birthweight and survival and improve lifetime production. Maintaining or increasing ewe liveweight during pregnancy and lactation may also result in heavier ewes the following year and higher ovulation rates. Pregnancy and lactation are also periods of increased susceptibility to metabolic disturbances. The composition of young crops increases this susceptibility. Pregnancy toxaemia, hypocalcaemia and hypomagnesaemia can influence ewe health and fetal survival. Chronic acidosis and excessive ammonia absorption from rapid introduction of pregnant ewes onto young crops may risk appetite loss and increase susceptibility to pregnancy toxaemia. Low magnesium and sodium combined with high potassium increases the risk of grass tetany. Most young crops (except canola) also have a tetany index >2.2, indicating a high risk of grass tetany. The elevated potassium also contributes to a high dietary cation–anion difference of approximately +49 mEq/100 g DM and this may cause metabolic alkalosis and hypocalcaemia. Pregnancy toxaemia, hypocalcaemia and grass tetany are all potential causes of increased ewe mortality. Pregnancy and/or lactation outcomes will also be influenced by a deficiency of trace elements. Grazing young crops in areas with a history of selenium, copper, iodine and cobalt deficiency will increase susceptibility to deficiency by increasing growth and feed intake. In conclusion, the grazing of young growing crops presents new opportunities for increased production and stocking rates in the mixed-farming zones. The value of this feed source is well recognised by some producers. While growing crops have a highly productive potential, they also come with an increased risk of a range metabolic disturbances and nutritional imbalances. These risks can be minimised by regular monitoring of livestock and crop biomass and the provision of mineral supplements.

Abstract This presentation will highlight historic discoveries in mineral metabolism in ruminants. At least 15 minerals can be classified as essential based on their involvement in one or more metabolic functions in mammals. Deficiencies of all essential minerals have occurred naturally or have been induced experimentally in ruminants. Cobalt was shown to be essential for ruminants in 1935 based on its ability to correct naturally occurring deficiency signs in Australia. This discovery occurred 13 years before cobalt was shown to a component of vitamin B12. Low serum magnesium concentrations also were associated with grass tetany in cattle before magnesium was found to be essential for the rat in 1931. The value of supplemental salt for cattle was demonstrated in the 1800’s and a salt deficiency was experimentally induced in dairy cows in 1905. Over 50 years later sodium was identified as the mineral primarily responsible for salt deficiency. Naturally occurring deficiencies of phosphorus and copper were observed in grazing ruminants shortly after they were reported to be essential for rats. Copper toxicosis also became recognized as a practical problem, especially in some breeds of sheep. Selenium was shown to prevent white muscle disease in 1958. Because of its known toxicity and lack of a specific metabolic function, it was not until 1979 that Food and Drug Administration approved the addition of 0.1 mg Se/kg DM (later increased to 0.3 mg/kg) from inorganic sources to ruminant diets. This approval occurred after the identification of glutathione peroxidase as a selenium metalloenzyme in 1972. In 2009, the Food and Drug Administration approved the use of chromium propionate as a source of supplemental chromium for cattle at levels up to 0.5 mg Cr/kg DM. The approval of chromium propionate was based on its safety and ability to enhance insulin sensitivity in cattle.

The effects of nitrogen (N) fertiliser (0–200 kg/ha) on mass, botanical composition, and N concentration (%) in herbage were examined in nine 2- or 3-year rate × time of application experiments, 14 single-year annual rate of application experiments and 15 short-term spring rate of application experiments, at 27 sites in the Mt Lofty Ranges, South Australia, in 7 years between 1970 and 1979, inclusive. Effects on in vitro digestibility and concentrations of other nutrients in herbage were examined in selected experiments.Annual applications of 200 kg N/ha increased herbage mass by an average of 2.8 t/ha (57% increase), over the average yield of unfertilised pasture of 4.6 t/ha. Subterranean clover was eliminated from the sward with this rate of N application, although this may have been exacerbated by the experimental methods used. N fertiliser application increased herbage mass throughout the growing season, except in autumn 1972 when low rainfall restricted growth and about half of the experiments were not harvested. In 5 of the 126 individual harvests, herbage mass did not respond positively to N fertiliser applications, even though clover composition of herbage declined.A single application of 50 kg N/ha in autumn increased herbage mass, 6–8 weeks later, by an average 11�kg�DM/kg N, but this N effect only persisted to a subsequent harvest in about half of the experiments, with an average residual effect of 25%. Commonly, a response to N fertiliser in the first and/or second harvests was followed by a non-responsive period and then a depression in herbage mass, where no further N fertiliser was applied. With repeated N fertiliser applications, the average responses to 50� kg� N/ha were 11 kg DM/kg N in late winter and also in early spring, similar to the autumn response, and 18�kg�DM/kg N in late spring. In a later study, a single application of 50 kg N/ha in spring, for silage or hay conservation, increased herbage mass by an average of 1.3 t/ha in late spring while the average response to 100 kg N/ha was 2.0 t/ha. Clover composition declined but was rarely eliminated from the sward by these N rates when applied only in spring.From early winter to early spring, N concentration in herbage from unfertilised pasture ranged from 3 to 4% N and then progressively declined. Relationships between herbage N concentrations and increasing N rates were either linear or curvilinear in early and late winter, whereas in spring, many of these responses to N fertiliser were sigmoidal, with a decline in herbage N concentrations being observed at low N rates. Nitrogen fertiliser applied throughout the growing season had little effect on in vitro digestibility for a wide range of pasture compositions. However, in vitro digestibility of a pure grass pasture was increased early in the growing season by applications up to 50 kg N/ha, but was depressed by the same N rates applied in late spring. Consistently, an increase in N had the following effect on the concentration of other herbage nutrients: K�increased; Ca decreased becoming more pronounced as the growing season progressed; P decreased in late spring; and Cu fell in autumn. The content of these nutrients in harvested herbage usually increased with increasing N rate, particularly when associated with large herbage mass responses to N fertiliser. The K : (Ca + Mg) ratio in herbage, a criterion for grass tetany, increased detrimentally with increasing N rate. Strategies are proposed for using N fertiliser on rain-fed pasture in the Mt Lofty Ranges.

Upaya-upaya apa yang dapat dilakukan pemerintah Indonesia dan Australia untuk memperkuat kembali hubungan bilateral Indonesia Australia? Pertanyaan ini tepat untuk diangkat, mengingat Presiden Joko Widodo (Jokowi) resmi dilantik ketika hubungan Indonesia-Australia sekali lagi berada pada titik rendah menyusul terkuaknya upaya skandal penyadapan yang dilakukan para agen intelijen Australia terhadap sejumlah petinggi Indonesia. Situasi kemudian semakin memburuk menyusul penolakan Presiden Jokowi atas permohonan grasi dua terpidana mati warga Australia yang dinyatakan bersalah tahun 2006 sebagai otak perencanaan penyelundupan heroin dari Bali. Tulisan ini berpendapat bahwa kedua pemerintahan dapat belajar pada praktek yang pernah dilakukan semenjak pertengahan tahun 1980an, yaitu membangun kembali hubungan bilateral yang diawali dengan diplomasi pertemanan. Komunikasi hotline langsung antar pemerintah kedua belah pihak diperluas sementara hubungan antar-orang tidak saja diperluas tetapi juga diperdalam. Cara ini membuka banyak kesempatan bagi kedua pihak dapat menemukan kepentingan-kepentingan serupa, yang selanjutnya tentu saja menjadi benih-benih unggul demi membangun kerjasama yang semakin lebih berarti ke depan.

Pasture yield in dairy grazing systems is critical to supplying sufficient feed for milking cows and maintaining productivity. In the Australian dairy industry, ryegrass and clover are common grasses used in grazed pastures. Dairy shed effluent (DSE), the wastewater produced from washing down the dairy holding yards during and after milking, is generally managed through application to pasture as a fertilizer substitute/supplement following partial treatment in stabilization ponds. The aim of this study is to assess the benefits of applying sludge and supernatant collected from two-stage DSE pond systems to ryegrass pasture. A pot experiment was conducted which involved applying pond sludges and supernatant to soil seeded with ryegrass. The application rates of the pond by-products were set according to their labile (plant available) phosphorus content. Ryegrass yield and leachate generated from each of the pots were recorded, and samples were collected for analysis of nutrients and other parameters. The ryegrass grown in soil treated with pond sludge and supernatant yielded greater dry matter (DM) with higher nutrient content than untreated control pots. In addition, pots treated with pond sludge exhibited lower rates of phosphorus leaching from the soil compared with pots treated with supernatant. Thus, pond sludge retained more plant available phosphorus in soil than both the control and pond supernatant treatment. The potassium to calcium/magnesium ratios in the ryegrass in the pots treated with pond sludge and supernatant were below the recommended upper limit for grazing. Therefore, the application of pond sludges on the dairy paddocks was found to be superior to applying supernatant in terms of utilization and conservation of phosphorus within the dairy farm and presents low risks of groundwater pollution and grass tetany.

Over the last 60 years, grass tetany has been recognised as a significant lethal condition in sheep and cattle.Outcomes from this study include documentation of the likely precursors to grass tetany, ways to recognise these precursors, and long term practices that will enable producers to minimise livestock deaths. The benefit of this research to beef producers is that the environmental circumstances thought to be associated with outbreaks of grass tetany have been identified, along with remedial action that can be taken to prevent deaths occurring.Recommendations to industry on best practice to be adopted by leading producers to minimise outbreaks of grass tetany are made.This study provides an alternate strategy for the management of grass tetany in beef cattle, to the more clinical approaches previously recommended. It is suggested that losses from this economically important metabolic disease can be minimised if management practices of beef cattle producers in eastern Australia can incorporate a more holistic approach to farm management, which takes account of the soil/plant/animal/climate inter-relationships.
Master of Science (Hons)

Over the last 60 years, grass tetany has been recognised as a significant lethal condition in sheep and cattle.Outcomes from this study include documentation of the likely precursors to grass tetany, ways to recognise these precursors, and long term practices that will enable producers to minimise livestock deaths. The benefit of this research to beef producers is that the environmental circumstances thought to be associated with outbreaks of grass tetany have been identified, along with remedial action that can be taken to prevent deaths occurring.Recommendations to industry on best practice to be adopted by leading producers to minimise outbreaks of grass tetany are made.This study provides an alternate strategy for the management of grass tetany in beef cattle, to the more clinical approaches previously recommended. It is suggested that losses from this economically important metabolic disease can be minimised if management practices of beef cattle producers in eastern Australia can incorporate a more holistic approach to farm management, which takes account of the soil/plant/animal/climate inter-relationships.