Nutritional strategies for the prevention of hypocalcaemia at calving for dairy cows in pasture-based systems

This review considers the current literature on the macro-mineral nutrition of the soon-to-calve, or transition, dairy cow. Calcium is the main focus, since milk fever (clinical hypocalcaemia) appears to be the most common mineral-related problem faced by the transition cow Australia-wide. The importance of minimising calcium intake and optimising the balance of the key dietary electrolytes, sodium, potassium, sulfate, and chloride, in the weeks before calving is highlighted. Excess dietary potassium can, in some situations, induce milk fever, perhaps even more effectively than excess calcium. Excess sodium remains under suspicion. In contrast, excess dietary chlorine and, to a lesser extent, sulfur can improve the ability of the cow to maintain calcium homeostasis. Diets that promote either a hypomagnesaemia or hyperphosphataemia have also the potential to precipitate milk fever at calving. Current prevention strategies focus on the use of forages with moderate to low levels of calcium, potassium, and sodium, and also rely on or utilise addition of chloride and sulfate in the form of 'anionic' feeds. Anionic salts are one example of an anionic feed. However, legitimate questions remain as to the effectiveness of anionic salts in pasture-feeding systems. The causes and prevention of milk fever are considered from the perspective of the variety of Australian feedbases. Impediments to the use of anionic feeds in Australia feeding systems are outlined. The potential for improving maternal reserves of calcium around calving to reduce the risk of milk fever is also discussed.

Balancing acts: Respiratory sensations, motor control and human posture

1. The present brief review covers some novel aspects of integration between respiration and movement of the body. 2. There are potent viscerosomatic reflexes in animals involving small-diameter pulmonary afferents that, when excited, would limit exercise. However, recent studies using lobeline injections to excite pulmonary afferents in awake humans suggest that there is no evoked reflex motoneuronal inhibition. Instead, the noxious respiratory sensations generated by the vagal afferents may be crucial in the decision to stop exercise. 3. While respiratory movements may affect limb movements, the control of the trunk and limbs can involve interaction (and even interference) with key respiratory muscles, such as the diaphragm. Recent studies have revealed that not only does the diaphragm receive feed-forward drive prior to some limb movements, but that it also contracts both phasically and tonically during repetitive limb movements. 4. Thus, challenges to posture can indirectly challenge ventilation, while coordinated diaphragm contraction may contribute to control of the trunk.

Production of the baculovirus-expressed dengue virus glycoprotein NS1 can be improved dramatically with optimised regimes for fed-batch cultures and the addition of the insect moulting hormone, 20-Hydroxyecdysone

A perennial problem in recombinant protein expression is low yield of the product of interest. A strategy which has been shown to increase the production of baculovirus-expressed proteins is to utilise fed-batch cultures. One disadvantage of this approach is the time-consuming task of optimising the feeding strategy. Previously, a statistical optimisation routine was applied to develop a feeding strategy that increased the yield of beta-Galactosidase (beta-Gal) by 2.4-fold (Biotechnol. Bioeng, 59 (1998) 178). This involves the single addition of nutrient concentrates (amino acids, lipids. glucose and yeastolate ultrafiltrate) into Sf9 cell cultures grown in SF900II medium. In this study, it is demonstrated that this optimised fed-batch strategy developed for a high-yielding intracellular product beta-Gal could be applied successfully to a relatively low-yielding glycosylated and secreted product such as the dengue virus glycoprotein NS1. Optimised batch infections yielded 4 mug/ml of NS1 at a peak cell density of 4.2 x 10(6) cells/ml. In contrast. optimised fed-batch infections exhibited a 3-fold improvement in yield, with 12 mug ml of NS1 produced at a peak cell density of 11.3 x 10(6) cells/ml. No further improvements in yield were recorded when the feed volumes were doubled and the peak cell density was increased to 23 x 10(6) cells/ml, unless the cultures were stimulated by the addition of 4 mug/ml of 20-Hydroxyecdysone (an insect moulting hormone). In this case, the NS1 yield was increased to 20 mug/ml. which was nearly 5-fold higher than optimised batch cultures. (C) 2002 Elsevier Science B.V. All rights reserved.

The effects of level of dietary protein on the milk production and rumen physiology of dairy cows fed a diet based on a tropical grass hay

zFour rumen-fistulated, multiparous Holstein-Friesian cows in early lactation were offered mixed diets based on rhodes grass hay (Chloris gayana) cv. Callide containing 13, 14, 15 or 16% crude protein (CP) on a dry matter basis, in a 4 x 4 latin square design. The estimated undegradable protein concentration in these diets was similar with rumen degradable protein concentration varying. Cows fed a diet containing 13% CP had lower (P = 0.07) milk yields than cows in other treatments (20.4 vs 21.9, 22.0 and 22.2 L/d for 13, 14, 15 and 16% CP, respectively). A positive linear relationship was found (P = 0.06) between organic matter intake and dietary CP%. There were negative linear relationships between dietary CP% and digestibilities of dry matter (P = 0.09), organic matter (P = 0.06) and neutral detergent fibre (P = 0.02). Feeding a diet containing 13% CP resulted in significantly lower (P = 0.001) molar proportions (%) of rumen valerate in comparison with other treatments. The molar proportions of isovalerate differed (P = 0.001) between treatments (0.66, 0.78, 0.89 and 1.04%) for 13, 14, 15 and 16% CP, respectively). Dietary protein level had no effect on rates of passage, in situ digestion of rhodes grass hay or ratios of allantoin: creatinine in urine. These data showed that increasing the dietary CP concentration of lactating cows fed diets based on rhodes grass hay increased intakes and not significantly improved at dietary CP concentrations above 14% DM.

Effects of dietary level of protein, lysine and methionine and strain of bird on production and egg yolk cholesterol

The effects of dietary level of protein (151, 181 g/kg), lysine (nil, 10g L-lysine hydrochloride/kg) and methionine (nil, 5g DL-methionine/kg) on the production performance and egg yolk cholesterol of two strains of birds were studied for 12 weeks. Birds fed on the high protein diet had higher body weight gain, feed conversion ratio (FCR), rate of lay, egg weight and mass and yolk weight and mass. A high lysine diet decreased feed intake and improved FCR. High dietary level of methionine increased egg yolk cholesterol. There were differences between strains of laying bird in feed intake, rate of lay, egg and yolk weights and egg cholesterol content. It is concluded that strain of bird and dietary level of protein and lysine influenced the production performance of birds. Whilst, egg yolk cholesterol was not reduced by any of the factors studied.

Practical and economic advantages of choice feeding systems for laying poultry

Poultry can be managed under different feeding systems, depending on the husbandry skills and the feed available. These systems include the following: (1) a complete dry feed offered as a mash ad libitum; (2) the same feed offered as pellets or crumbles ad libitum; (3) a complete feed with added whole grain; (4) a complete wet feed given once or twice a day; (5) a complete feed offered on a restricted basis; (6) choice feeding. Of all these, an interesting alternative to offering complete diets is choice feeding which can be applied on both a small or large commercial scale. Under choice feeding or free-choice feeding birds are usually offered a choice between three types of feedstuffs: (a) an energy source (e.g. maize, rice bran, sorghum or wheat); (b) a protein source (e.g. soyabean meal, meat meal, fish meal or coconut meal) plus vitamins and minerals and (c), in the case of laying hens, calcium in granular form (i.e. oyster-shell grit). This system differs from the modern commercial practice of offering a complete diet comprising energy and protein sources, ground and mixed together. Under the complete diet system, birds are mainly only able to exercise their appetite for energy. When the environmental temperature varies, the birds either over- or under-consume protein and calcium. The basic principle behind practising choice feeding with laying hens is that individual hens are able to select from the various feed ingredients on offer and compose their own diet, according to their actual needs and production capacity. A choice-feeding system is of particular importance to small poultry producers in developing countries, such as Indonesia, because it can substantially reduce the cost of feed. The system is flexible and can be constructed in such a way that the various needs of a flock of different breeds, including village chickens, under different climates can be met. The system also offers a more effective way to use home-produced grain, such as maize, and by-products, such as rice bran, in developing countries. Because oyster-shell grit is readily available in developing countries at lower cost than limestone, the use of cheaper oyster-shell grit can further benefit small-holders in these countries. These benefits apart, simpler equipment suffices when designing and building a feed mixer on the farm, and transport costs are lower. If whole (unground) grain is used, the intake of which is accompanied by increased efficiency of feed utilisation, the costs of grinding, mixing and many of the handling procedures associated with mash and pellet preparation are eliminated. The choice feedstuffs can all be offered in the current feed distribution systems, either by mixing the ingredients first or by using a bulk bin divided into three compartments.

Structure of the gut contents of Trichogramma australicum Girault (Hymenoptera : Trichogrammatidae) larvae fixed in situ in eggs of its host Helicoverpa armigera (Hubner) (Lepidoptera : Noctuidae)

Trichogramma australicum larvae develop most rapidly in younger eggs of its host, the pest lepidopteran Helicoverpa armigera . To establish how the developmental stage of the host affects the diet of T. australicum , larvae were fixed in situ in eggs of H. armigera of different ages and the structure of the egg contents and parasitoid gut contents examined histologically. Larvae feeding on newly laid host eggs contain primarily yolk particles in their gut, while larvae feeding on older hosts contain necrotic cells and yolk particles. The gut of T. australicum larvae does not contain organised tissue remnants, indicating that larvae feed primarily by sucking food into their pharynx and feed best on a mixture of particulate semisolids in a liquid matrix. Secretory structures of T. australicum larvae that could be involved in modifying the host environment were examined. The hindgut is modified to form an anal vesicle with a number of attributes suggesting that it may be a specialised secretory structure. The paired salivary glands open to the exterior via a common duct.

Habitat choice and vigilance behaviour of brush-tailed rock-wallabies (Petrogale penicillata) within their nocturnal foraging ranges

Habitat choice by brush-tailed rock-wallabies (Petrogale penicillata) in south-east Queensland was investigated by comparing the attributes of the nocturnal foraging locations that they selected with those of random locations within a radius of 50 m. Brush-tailed rock-wallabies were shown to select foraging locations on the basis of forage quality and/or their ability to see predators, rather than protection from predators amongst vegetation that could conceal them. Habitat choice may have been affected by limited food availability, as this study was conducted in the winter dry season. The attributes of foraging locations that brush- tailed rock-wallabies perceived as increasing their predation risk were assessed by recording the proportion of time that brush- tailed rock-wallabies spent vigilant while foraging. To measure vigilance, focal animals were observed with a night- vision scope for two minutes and the proportions of time spent vigilant and feeding were recorded. No measured feature of foraging locations was related to higher vigilance levels, suggesting that brush- tailed rock-wallabies did not alter their vigilance whether sheltered amongst grass tussocks or in open habitat, or whether feeding on good quality or poorer quality vegetation. Vigilance levels significantly declined as overnight temperatures decreased, which may have resulted from higher energy requirements of brush- tailed rock-wallabies during winter. The only factors that were found to significantly increase vigilance levels were high winds and moonlit nights. On bright nights, brush- tailed rock-wallabies were very unsettled and during high winds they often did not emerge to feed. More information is needed about how macropods detect predators at night before the effects of wind and light intensity upon vigilance can be fully understood.

Variables affecting the fine grinding of minerals using stirred mills

Base metal resources are becoming more fine-grained and refractory and minerals separation processes require these ores to be milled to increasingly finer sizes. To cope with very fine grinding to below a P-80 of approximately 15 mum stirred milling technology has been adopted from other industries Neither this technology, nor the basic concepts of fine grinding, are well understood by the minerals processing industry. Laboratory studies were therefore carried out in order to investigate fine milling using different types of stirred mills. The variables analysed were stirrer speed, grinding media type and size, slurry solids content as well as the feed and product size. The results of the testwork have shown that all of these variables affect the grinding efficiency. The ratio of media size to material size was found to be of particular significance. The results were also analysed using the stress intensity approach and the optimum stress intensity ranges for the most efficient grinding were determined. Application of the results for process optimisation in the industrial size units is also discussed in this paper. (C) 2003 Elsevier Science Ltd. All rights reserved.

The JK three-product cyclone - performance and potential applications

In spite of their wide application in comminution circuits, hydrocyclones have at least one significant disadvantage in that their operation inherently tends to return the fine denser liberated minerals to the grinding mill. This results in unnecessary overgrinding which adds to the milling cost and can adversely affect the efficiency of downstream processes. In an attempt to solve this problem, a three-product cyclone has been developed at the Julius Kruttschnitt Mineral Research Centre (JKMRC) to generate a second overflow in which the fine dense liberated minerals can be selectively concentrated for further treatment. In this paper, the design and operation of the three-product cyclone are described. The influence of the length of the second vortex finder on the performance of a 150-mm unit treating a mixture of magnetite and silica is investigated. Conventional cyclone tests were also conducted under similar conditions. Using the operational performance data of the three-product and conventional cyclones, it is shown that by optimising the length of the second vortex finder, the amount of fine dense mineral particles that reports to the three-product cyclone underflow can be reduced. In addition, the three-product cyclone can be used to generate middlings stream that may be more suitable for flash flotation than the conventional cyclone underflow, or alternatively, could be classified with a microscreen to separate the valuables from the gangue. At the same time, a fines stream having similar properties to those of the conventional overflow can be obtained. Hence, if the middlings stream was used as feed for flash flotation or microscreening, the fines stream could be used in lieu of the conventional overflow without compromising the feed requirements for the conventional flotation circuit. Some of the other potential applications of the new cyclone are described. (C) 2003 Elsevier Science B.V. All rights reserved.

Development of a more efficient classifying cyclone

A more efficient classifying cyclone (CC) for fine particle classification has been developed in recent years at the JKMRC. The novel CC, known as the JKCC, has modified profiles of the cyclone body, vortex finder, and spigot when compared to conventional hydrocyclones. The novel design increases the centrifugal force inside the cyclone and mitigates the short circuiting flow that exists in all current cyclones. It also decreases the probability of particle contamination in the place near the cyclone spigot. Consequently the cyclone efficiency is improved while the unit maintains a simple structure. An international patent has been granted for this novel cyclone design. In the first development stage-a feasibility study-a 100 mm JKCC was tested and compared with two 100 min commercial units. Very encouraging results were achieved, indicating good potential for the novel design. In the second development stage-a scale-up stage-the JKCC was scaled up to 200 mm in diameter, and its geometry was optimized through numerous tests. The performance of the JKCC was compared with a 150 nun commercial unit and exhibited sharper separation, finer separation size, and lower flow ratios. The JKCC is now being scaled up into a fill-size (480 mm) hydrocyclone in the third development stage-an industrial study. The 480 mm diameter unit will be tested in an Australian coal preparation plant, and directly compared with a commercial CC operating under the same conditions. Classifying cyclone performance for fine coal could be further improved if the unit is installed in an inclined position. The study using the 200 mm JKCC has revealed that sharpness of separation improved and the flow ratio to underflow was decreased by 43% as the cyclone inclination was varied from the vertical position (0degrees) to the horizontal position (90degrees). The separation size was not affected, although the feed rate was slightly decreased. To ensure self-emptying upon shutdown, it is recommended that the JKCC be installed at an inclination of 75-80degrees. At this angle the cyclone performance is very similar to that at a horizontal position. Similar findings have been derived from the testing of a conventional hydrocyclone. This may be of benefit to operations that require improved performance from their classifying cyclones in terms of sharpness of separation and flow ratio, while tolerating slightly reduced feed rate.

An energy-based model for swing hammer mills

An energy-based swing hammer mill model has been developed for coke oven feed preparation. it comprises a mechanistic power model to determine the dynamic internal recirculation and a perfect mixing mill model with a dual-classification function to mimic the operations of crusher and screen. The model parameters were calibrated using a pilot-scale swing hammer mill at various operating conditions. The effects of the underscreen configurations and the feed sizes on hammer mill operations were demonstrated through the fitted model parameters. Relationships between the model parameters and the machine configurations were established. The model was validated using the independent experimental data of single lithotype coal tests with the same BJD pilot-scale hammer mill and full operation audit data of an industrial hammer mill. The outcome of the energy-based swing hammer mill model is the capability to simulate the impact of changing blends of coal or mill configurations and operating conditions on product size distribution. Alternatively, the model can be used to select the machine settings required to achieve a desired product. (C) 2003 Elsevier Science B.V. All rights reserved.

Designing a 161-element Ku-band microstrip reflectarray of variable size patches using an equivalent unit cell waveguide approach

An equivalent unit cell waveguide approach (WGA) to designing 4 multilayer microstrip reflectarray of variable size patches is presented. In this approach, a normal incidence of a plane wave on an infinite periodic array of radiating elements is considered to obtain reflection coefficient phase curves for the reflectarray's elements. It is shown that this problem is equivalent to the problem of reflection of the dominant TEM mode in a waveguide with patches interleaved by layers of dielectric. This waveguide problem is solved using a field matching technique and a method of moments (MoM). Based on this solution, a fast computer algorithm is developed to generate reflection coefficient phase curves for a multilayer microstrip patch reflectarray. The validity of the developed algorithm is tested against alternative approaches and Agilent High Frequency Structure Simulator (HFSS). Having confirmed the validity of the WGA approach, a small offset feed two-layer microstrip patch array is designed and developed. This reflectarray is tested experimentally and shows good performance.

An electromagnetic-field method modeling of a radial line planar antenna with coupling probes

This communications describes an electromagnetic model of a radial line planar antenna consisting of a radial guide with one central probe and many peripheral probes arranged in concentric circles feeding an array of antenna elements such as patches or wire curls. The model takes into account interactions between the coupling probes while assuming isolation of radiating elements. Based on this model, computer programs are developed to determine equivalent circuit parameters of the feed network and the radiation pattern of the radial line planar antenna. Comparisons are made between the present model and the two-probe model developed earlier by other researchers.

Trichostome ciliates from Australian marsupials. IV. Distribution of the ciliate fauna

Trichostome ciliates are associated with many different lineages of herbivorous mammals but there are few comparative studies of these associations in each lineage of herbivores. Here the occurrence of the ciliate fauna in a range of herbivorous marsupials (diprotodonts) is investigated and compared with that of ruminants. A total of 371 potential host animals, representing 33 species and 7 families, were examined for the presence of ciliates. The prevalence of endocommensal ciliates within individual host species varied between 0 and 100%. Of the different dietary groups of marsupials examined, only foregut (macropodids) and hindgut (vombatids) fermentative herbivores were found to harbour ciliates; carnivorous (dasyurids), omnivorous (peramelids) and midgut fermenting herbivores (phalangeroids) all lacked ciliates. The majority of ciliate species were oioxenic, several occurred in closely related hosts and some were able to colonise unnatural hosts in captive populations. Ciliate prevalences were found to vary at all levels: between hosts of different species, between conspecific hosts collected at different localities or seasons and between conspecific hosts at one collecting locality. The faunal composition of the 2 marsupial families which harboured ciliates differed greatly: the vombatid fauna was composed exclusively of amylovoracids whereas the macropodids harboured amylovoracids, polycostids and macropodiniids. In comparison to the ciliate fauna of ruminants, the fauna of macropodids is both depauperate and much more host specific. Low species richness in each host may be due to the large numbers of stomach nematodes in macropodids which compete with and may prey upon the ciliates within the stomach. The high levels of host specificity are probably due to different patterns of ciliate transmission in macropodids as they do not ruminate, eructate or feed indiscriminantly on pasture contaminated with saliva containing ciliates.