Agriculture and Food Systems - Theses
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ItemNutritional modification of muscle long-chain omega-3 fatty acids in lambs : effects on growth, and composition and quality of meat( 1999)Three experiments were conducted to investigate the effects of dietary supplements rich in omega-3 fatty acid on muscle omega-3 fatty acid deposition. The consequential effects on growth performance of lambs, colour and lipid oxidative stability of muscle over refrigerated display, and the sensory properties of cooked meat were also examined. A mixture of lucerne chaff : oaten chaff was used as basal diet, offered in different proportions were fed to lambs ad libitum (Expt. 1) or at 90% ad libitum (Expts. 2 and 3). Such mixtures of roughage diet support slow growth and provide a feed quality pattern similar to late spring to late summer pasture. In Expt. 1, fish meal (7%), canola meal (8%) and soymeal (7%) as natural feed supplements were compared in lambs fed low quality roughage diet. In Expt. 2, fish meal (9%) and oilseed supplements either in unprotected form (rapeseed - 7%) or in protected form (ground canola seed - 6%) were examined in lambs on medium quality roughage diet. Lipids and the proteins in the ground canola seed were treated (RUMENTEK) with aldehyde to protect them from the rumen microbial activity. Fish meal (9%), fish oil (1.5%), fish oil (1.5%) with sunflower meal protein (9%),' and sunflower meal protein alone (10.5%) (a commercial product of a protein supplement from RUMENTEK) were compared in lambs fed medium quality roughage diet in Expt. 3. Long-chain omega-3 fatty acids (eicosapentaenoic acid + docosahexaenoic acid) in muscle longissimus thoracis was increased modestly and markedly with fish meal and fish oil alone or with sunflower meal protein diet, respectively. These long-chain fatty acids were deposited in the muscle structural phospholipid rather than in storage triglycerides. All the diets mentioned above also significantly reduced omega-6:omega-3 fatty acid ratio in meat which is another beneficial effect, as the dietary recommendation in many countries has been to reduce the ratio of omega-6:omega-3 in human diet. Soymeal diet increased modestly both the omega-3 and omega-6 fatty acid content of muscle longissimus thoracis resulting in no differences in the omega-6:omega-3 ratio of the meat. A supplement of protected canola seed significantly increased the precursors of omega-6 (linoleic) and omega-3 (linolenic) but not the long-chain analogues such as arachidonic acid (omega-6) and eicosapentaenoic, docosahexaenoic acid (omega-3), respectively. The marked increase in linoleic acid content was in both triglyceride and phospholipid fractions of muscle longissimus thoracis but the modest increase in linolenic acid content was only in triglyceride fraction of meat. Supplements of canola meal used in Expt. 1, unprotected rapeseed used in Expt. 2 and protected sunflower meal protein used in Expt. 3 did not alter the fatty acid composition of muscle longissimus thoracis compared with lambs fed the control diet in that particular experiment. The increased level of long-chain omega-3 fatty acid and/or omega-6 fatty acid with the lipid supplements discussed above did not significantly affect the meat colour stability and lipid oxidative stability of fresh and vacuum packaged meat over the storage at refrigerated display. This suggests that the conditions under which the animals are grown (grazing vs grain fed or feedlot) and the species of animal are important in determining the oxidative stabilities of meat by altering the levels of muscle vitamin E concentrations at slaughter. The level of inclusion of lucerne chaff in the basal diet is an important factor in improving the redness of meat indicated by the a*-value; a higher level of lucerne chaff intake is more likely to be associated with increased intake of vitamin E. Thus colour and lipid oxidative stabilities of meat can be improved in red meat animals that are on poor quality diets by the inclusion of lucerne chaff in their diet. The sensory properties of cooked meat evaluated in the present study were not affected by the significant increase in muscle long-chain omega-3 fatty acid or omega-6 fatty acid content with fish oil and protected canola seed supplements, respectively. Addition of protected sunflower meal as a protein supplement together with fish oil significantly lowered the ratings of flavour and overall acceptability of meat compared with the control lambs. The results demonstrate that the common `lamby' and `muttony' flavour and aroma attributes were not hidden by any of the dietary treatments. These two characters associated with the species flavour and aroma were recognised by the panellists as a distinct attribute. Dry matter intake was not adversely affected by any of the lipid supplements used in the present study. Feed conversion efficiency was highest with fish meal diet on both low and medium quality roughage diets. At medium quality roughage-based diet, Feed conversion efficiency was modestly improved by protected canola seed diet but other supplements providing either natural (unprotected rapeseed) or protected protein (protected sunflower meal) did not support significant differences compared with basal diet. The significant increase in liveweight gain with fish meal diet reflected a significant increase in hot carcass weight compared with all other supplemented lambs either on low or on medium quality roughage diet. Protected lipid and protein offered by protected canola seed diet significantly and moderately increased liveweight gain and hot carcass weight from control diet but not different from unprotected rapeseed diet. The greatest muscle deposition was with the fish meal diet and is attributed mainly to the increased amount of protein and energy absorbed from the small intestine of those lambs. In addition to energy and protein absorption, the alteration of omega-3 polyunsaturated fatty acids in muscle membranes may have a further influence in lean meat production. In terms of carcass gain and intramuscular fat deposition of fishmeal and fish oil fed lambs, the results also lead to a hypothesis that modifying omega-3 polyunsaturated fatty acid of muscle membrane phospholipids may have an influence in improved muscle deposition in lambs by improving the insulin action at skeletal muscle site.
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ItemThe effect of growing location and time of sowing on the production of premium quality oilseeds in south-eastern Australia( 1998)New Brassica oilseeds with modified fatty acid profiles tailored to specific end-uses are being developed in southern Australia. However, the fatty acid composition of Brassicas are known to vary markedly with environmental conditions during growth. A series of experiments were conducted to establish the most appropriate regions and sowing times within south-eastern Australia for the production of high oleic acid canola (HOAC), low linolenic acid canola (LLAC) and high erucic acid rapeseed (HEAR). Controlled experiments were conducted to evaluate the, effects of water deficit and temperature stress on fatty acid composition of conventional canola, HOAC, LLAC and HEAR. Ten years of data from the advanced canola trials of Agriculture Victoria were analysed, and a three-year trial was undertaken to identify the south-eastern Australian locations which produced specialty cultivars with the highest oil and seed protein content, lowest glucosinolate concentration, and premium oil quality (i.e. most appropriate fatty acid composition). Two glasshouse trials were performed to determine the separate effects of severe water deficit and three days of high (32C) and very high temperatures (37C) at 10, 20 and 30 days after flowering (DAF) on the oil composition of a HEAR cultivar and HOAC cultivar. In contrast to earlier work on the effects of sustained high postflowering temperatures, three hot days had no effect on oil composition or yield of the two cultivars, except that 37/25C (day/night) from 30-33 DAF reduced erucic acid content of HEAR from 52% to 44%. Severe drought reduced the quality and yields of both cultivars. Erucic acid content of the HEAR cultivar decreased by up to 10% and the oleic acid content decreased by up to 4% with post-flowering drought. Within each year, most variation in the quality components of the three year field trial was due to site. Oil ,content and seed yield were highest, and seed protein content and glucosinolate concentration were lowest, in the cooler and wetter sites and years. Generally, warmer post-flowering conditions enhanced oleic acid content at the expense of linoleic and linolenic acids in the canola quality cultivars, although all regressions between quality and weather variables were fairly weak. In 1995, for. every 5C increase in the average temperature between flowering and maturity, oil content decreased and seed protein content increased by an average 4%, glucosinolate concentration increased by 4.0 ?mol/g, and the linoleic and linolenic acid content each decreased by 1-2% in the different canola quality types. Each 100 mm increase in rainfall between flowering and maturity increased yields by 0.4 t/ha and oil content by 1.6%, and reduced seed protein content by 0.5% and glucosinolate concentration by 1.1 ?mol/g, on average. Oil content was strongly negatively correlated with seed protein content (r=-0.75 for conventional canola). Upon removing the effects of year and cultivar from the ten year dataset, the mean oleic acid content, of conventional canota was very stable across regions, but varied more between years. Canola grown in - central Victoria and the Wimmera produced consistently high levels (>60%) of oleic acid. Canola consistently achieved a low linolenic acid content in central Victoria (<10.8%), and a moderate to low: linolenic acid content in the Wimmera. The Mallee produced canola with highly variable levels of oleic acid and linolenic acid, despite warm post-flowering temperatures which are known to increase oleic acid content. In the three year trial, time of sowing did not have a consistent effect. on the fatty acid composition of canola, probably due to the interactions between temperature and rainfall. These results identified central Victoria and the Wimmera as the most appropriate locations for the production of HOAC and LLAC cultivars. One year of data indicated that Wagga Wagga is capable of producing canola with extremely high oleic acid and low linolenic acid levels. The results of the three year trial identified lower south-eastern South Australia and the Victorian Wimmera as regions most conducive to the production of HEAR with consistently high levels of erucic acid. The erucic acid content of HEAR was often reduced by late sowing. However, this trend was not always observed, and possible reasons for deviations from trends have been discussed. One year of data demonstrated high levels of erucic acid in HEAR produced in the southern part of central Victoria. As the time of sowing did not have a consistent effect on the erucic acid content of HEAR, or the oleic and linolenic acid content of HOAC and LLAC, it was recommended that growers sow at the same time as recommended for conventional canola, to maximise yield and oil content.
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ItemControl of vegetative vigour of peach orchards( 1996)In the Goulburn/Murray Valley of South-Eastern Australia, orchard management aims to maximise productivity and ensure sustainability. Achievement of this objective relies on the control of excess vegetative vigour, minimisation of salinity and waterlogging damage and improvement of irrigation efficiency. The overall aim of this study was to identify the major controls over vegetative vigour under varying environmental conditions with a view to providing practical management strategies. Options which are currently available for control of vegetative vigour include dwarfing rootstocks, chemical growth regulators and summer pruning. Alternative systems which may be more suitable are Regulated Deficit Irrigation (RDI), saline irrigation and Restricted Root Volume (RRV). Regulated Deficit Irrigation (RDI) applied in a high-density peach orchard controlled vegetative growth (reduction of 50%) and maintained yield. RDI trees used less water than traditionally irrigated trees during the RDI period. This was attributed to reduced water availability and plant water status. Differences in water use continued after RDI due to a combination of tree size, leaf area and micro-advection. Irrigation with water of EC greater than 0.5 dS m-1 combined with RDI, reduced vegetative and fruit growth, yield and tree water use. Yield declined as a consequence of smaller leaf area, decreased photosynthetic activity and overall poor tree health. The adverse effects were largely attributed to chloride toxicity with leaf CI concentration approaching 3% dry matter. In a saline environment, RDI will require the inclusion of strategic leaching. A shallow non-saline water table combined with RDI initially enhanced vegetative growth. However, in the second season, adverse effects of both non-saline and saline water tables on tree growth and productivity were demonstrated. Tree water use was initially greater over the non-saline water table which contributed approximately 28% of total water used. Chloride concentrated in the leaves and fruit, while Na concentrated in the bark, butt wood and structural roots. These results demonstrate the need for both leaching of the soil and limiting drainage to the water table. Artificial drainage and/or accurate irrigation scheduling will be essential features of successful management. Restricted root volume (RRV) reduced tree growth although the effect decreased in the third and fourth seasons. Water stress (RDI) had little effect on tree growth despite considerable differences in plant water status. Trees in the smallest soil volume demonstrated difficulty in achieving adequate fruit size. There were significant differences in water use in response to soil volume and RDI management. Water use followed similar seasonal patterns as previously established. In summary, RDI is a viable management option for the control of vegetative growth in high density peach orchards and RRV is effective in controlling vegetative growth. More research is required, however, before RRV can be adopted by growers. Saline irrigation reduced vegetative growth and also productivity and is therefore not considered an option for control of vegetative vigour. Salinity and water tables should be managed to minimise their effect.
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ItemEffects of post-anthesis stress on grain filling and malting quality of barley( 1995)Malting quality is variable from year to year in many countries with Mediterranean or continental climates. Environmental stresses are thought to contribute to that variability. However, little information is available on the relationships between environmental conditions during grain growth and malting quality. Two of the most frequent environmental constraints during grain filling in many cereal-growing areas of the world are high temperature and drought. Short periods (ca. 5 days) of very high maximum temperature (>35C) are quite common during grain growth and have been identified as a potential source of variation in malting quality. Therefore, the main objectives of the present study, were to determine the effect of short periods of high temperature and drought on grain growth and malting quality of barley. The study involved seven experiments, in which short periods (5 days) of high temperature and drought, combined or alone, were imposed during grain filling on the malting cultivar Schooner. Where possible, other malting cultivars were included (Chapters 2 and 3). The effects of short periods of high temperature on grain yield and malting quality of barley were first assessed under field conditions using portable chambers with thermostatically-controlled electric heaters. High temperature imposed for 5 days (17 to 21 days after anthesis) with a maximum temperature of 40C maintained for 6 h per day reduced grain weight by 13% in Schooner and 25% in Parwan. There was a reduction in starch content and an increase in nitrogen content in the heat treatments, but B-glucan content was not affected. High temperature reduced the amount of 'maltable' grain by reducing grain size and increasing screening percentage, and also reduced malt extract by 3-7%, which represents a large decrease for the malting industry. The other experiments in this thesis were carried out under controlled-environment conditions, in order to overcome difficulties of temperature and humidity control. Short periods of high temperature were imposed for 5 or 10 days at mid-grain filling on Schooner and Franklin, with or without drought treatments. Short periods of high temperature reduced grain weight by 5%, while drought reduced it by 20%. High temperature and drought together resulted in the greatest reduction (30%). There was a reduction in starch content and an increase in diastatic power and ?-glucan degradation under stress. However, malt extract was not significantly affected. To determine the importance of timing of short periods of high temperature and drought on grain weight and malting quality, a glasshouse experiment was carried out in which Schooner barley was exposed to these stresses at early, mid or late grain filling. Individual grain weight was most sensitive to high temperature and drought treatments imposed early in grain filling (10-15 days after anthesis) and was less sensitive to later treatments. Starch was reduced in amount and quality, especially with early stresses during grain filling. However, malt extract was not significantly affected. Finally, two experiments were carried out in the Canberra phytotron to study the effects of the temperature regime before and after heat stress on grain growth and quality. In the first experiment, the hypothesis that under a gradual increase in temperature, plants could develop some acclimation was tested. Plants experiencing either a sudden or a gradual increase did not exhibit any differences in grain weight or malting quality, but increasing the temperature in two steps (so that plants were exposed to 30 or 34C for 2 h before a 40C heat stress), appeared to have produced acclimation, since the reduction in grain weight under the two step treatment was about half that of either sudden or gradual increase in temperature. In the second experiment, the hypothesis tested was that grain growth would recover better from short stress under cool (21/16C) than warm (27/22C and 30/250 conditions following that heat stress. The reduction in yield caused by heat stress was not alleviated by the succeeding moderately high temperatures. The following conclusions were derived from this study: (i) the reduction in grain weight ranged from 5 to 35% in response to short periods of high temperature and drought during grain filling in barley. The magnitude of the reduction depended on duration and timing of exposure, (ii) the reduction in grain weight was accompanied by an increase in screening percentage corresponding to a large reduction in amount of 'maltable grain', (iii) grain composition was altered by these stresses, and in general, starch content was most affected. There was a strong and positive relationship between the reduction in grain weight and starch content per grain (R2=0.92, P<0.001). In all the experiments, there were reductions in the volumes of both A- and B-type starch granules; however, the reduction in grain weight was mostly closely related to the reduction in the volume of Atype starch granules. The stress-induced increase in nitrogen percentage was smaller than expected, probably because post-anthesis availability of nitrogen was less limited than under typical field conditions. Grain ?-glucan content tended to be reduced under drought but there was no clear trend under heat stress, and (iv) malt extract was not highly responsive in any of the high temperature or drought experiments. Malt extract was reduced by 3 to 7% in the field experiments (Chapter 2) and by 5% in a glasshouse experiment (Chapter 5) with short periods of heat stress. Although small relative to the grain yield reductions observed, such changes in malt extract are large for the malting industry. High temperature and drought affected several components of malting quality in opposing directions, for example the stresses reduced starch content, which would tend to reduce malt extract but also tended to decrease ?-glucan and increase diastatic power which would tend to increase malt extract. The net result of these opposing changes was generally a minor effect of heat stress and drought on malt extract, even though the main quality components contributing to malt extract often strongly responded to these stresses.
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ItemReproductive development of wheat under different thermal and photoperiodic environments( 1995)The overall objective of the thesis was to advance knowledge concerning phenological development in wheat. Specifically, it examines the variability of response to the main environmental factors. These are mean temperature, vernalising temperature, and photoperiod. Responses were examined by changing the environmental factors in various combinations, and the generality of the responses was gauged by including different cultivars in each study. The thesis includes some simple mathematical descriptions of the responses. The thesis has seven chapters describing and analysing specific experiments. Each chapter has its own introduction, results, discussion and conclusions. Particular chapters examine (i) if thermal amplitude affects wheat development independently of mean temperature, (ii) whether there is variability in the sensitivity to mean temperature among different cultivars and phenophases in relation to cardinal (base and optimum) temperatures, (iii) whether genetic variability in response to vernalisation and photoperiod can be described with numerical parameters, and whether these parameters change with development, (iv) whether rate of change of photoperiod can affect wheat development independently of absolute photoperiod, and finally (v) whether the interactions between temperature x photoperiod are important modifiers of development. The durations of the developmental phases the seedling stage (Haun stage < 1) to terminal spikelet initiation and from then to anthesis showed no evidence of systematic change due to thermal amplitude (ranging from 0 to 14 C, around an average temperature of 19 C) in any of four cultivars examined. Final leaf number and phyllochron were not significantly affected by thermal amplitude. The same four cultivars were then subjected to a range of average temperatures between 10 and 25 C. The duration of the stage from seedling growth to anthesis was reduced as temperature increased towards 19 C. Further increase in temperature did not alter duration in the cultivars Condor, Rosella and Cappelle Desprez, but increased duration in Sunset. Rate of development towards anthesis generally increased curvilinearly with temperature, so the response was reassessed in greater detail by subdividing the full period to anthesis into three phases. All responses in all cultivars could then be described numerically within the linear constraints of the thermal time concept. Base and optimum temperatures increased as development progressed towards anthesis. Averaging across cultivars, base temperature rose from -1.9 to +8.1 C for the phases before and after terminal spikelet initiation, respectively. Optimum temperature also increased. Cultivars differed substantially in each of these parameters. The progressive increase in optimum temperature with phasic development was apparently the main reason why linear fits for the three phases appear curvilinear for the full phase to anthesis. Final leaf number was negligibly changed by temperature, but phyllochron was significantly reduced as temperatures increased to 19 C. Cultivars differed in their base temperature for leaf appearance but had a similar optimum temperature of approximately 22 C. It is concluded that cardinal temperatures not only change with phase of development, and are specific for each genotype, but also that they can be different for developmental processes that are occurring at similar times. A model partitioning the response to vernalisation into three parameters, viz. optimum vernalisation (Vo), vernalisation sensitivity (Vs) and basic length (Lb) was proposed to analyse the responses to vernalisation in the cultivars Odin, Robin, Rosella and Condor. Vernalisation lasted from 0 to 70 d after seed imbibition and significantly reduced the time to anthesis in all cultivars, changing all three parameters in each of the pre-anthesis phenophases considered. All cultivars exhibited quantitative responses to all levels of vernalisation during the vegetative phenophase to double ridge. However, for the reproductive phases, Odin failed to reach anthesis if treated with less than 2 weeks vernalisation, indicating that vernalisation affects development beyond the vegetative phase. There were significant progressive reductions in final leaf number with longer periods of vernalisation. For the most sensitive cultivars, Rosella and Odin, the number of leaves appearing after double ridge was reduced by vernalisation. However, the number of leaves appearing after double ridge was only partially associated with the length of the reproductive phase. In the sensitive cultivars, phyllochron was shorter early in plant development than later, the change occurring at about leaf 6. In a parallel study, the vernalisation period was interrupted by a 3 d period of 18 C to investigate whether a moderate temperature can produce devernalisation. Partial devernalisation occurred in Rosella and Odin. In a field experiment, photoperiod was extended artificially in five treatments up to terminal spikelet initiation viz.; natural photoperiod (rate of change of photoperiod=2.3 min d-1 ), two faster rates of change (9.8 and 13.1 min d-1 ) and two constant photoperiods of 14.0 and 15.5 h. After terminal spikelet initiation, the two constant photoperiods were extended to 15.0 and 16.5 h, respectively, and treatments were randomly re-allocated. The rate of development from seedling emergence to terminal spikelet initiation responded to increases in photoperiod in both cultivars but there was no effect of rate of change of photoperiod. Phyllochron did not alter during plant development or in response to the photoperiod regimes. Finally, the effects on development of photoperiod (9, 12, 15, 17, 19 and 21 h) and temperature (21/17 and 16/12 C) in combination were studied. Again, four cultivars (a non-segregating awned selection of Sunset, Sunsetaw, Condor, Rosella and Cappelle Desprez) were used. Increases in both photoperiod and temperature always reduced the time to heading, but genotypes differed substantially in the magnitude of their responses to the individual environmental variables, and also in their responses to the different combinations. The interaction effects were sometimes greater than the individual effects. A model of the response of wheat development to temperature was proposed which includes the effects of photoperiod not only on thermal time but also on base temperature. Differential responses to short photoperiods were evident amongst genotypes, indicating that more than one degree of sensitivity to photoperiod might be possible for a single cultivar. Final leaf number on the main culm increased with shortening photoperiod, but was unaffected by temperature as observed previously. Although time to heading was always linearly related to final leaf number, the results suggest that photoperiod acted at least partially independently on the timing of heading and on final leaf number. The responses to photoperiod x temperature during three phenophases (pre-double ridge, from then to terminal spikelet initiation, and from then to heading) were assessed using a mathematical description which partitioned the response of each cultivar and phenophase into one or two photoperiodic sensitivities (Ps and Ps2), an actual maximum length (Lma) of the phase, which occurs at the critical photoperiod (Pc), a potential maximum length (Lmp) and a basic length (Lb) of the phase that occurs at the optimum (Po) or longer photoperiods. The duration of the early phase to double ridge was quantitatively affected by photoperiod and could be described by a single sensitivity value (Ps) which differed in magnitude between cultivars. The Po also differed amongst cultivars, and was longer at the higher temperature, while Lb during this phase showed a significant cultivar x temperature interaction. The duration of the phase from double ridge to terminal spikelet initiation was quantitatively responsive to photoperiod in all cultivars, and the response was affected by temperature. However, the responses of these two phases were different, as judged by their parameters. In this phase, Condor, Rosella and Cappelle Desprez showed a 3 to 5 fold greater sensitivity to very short photoperiods (Ps2) than to longer photoperiods (Ps). The response to photoperiod between terminal spikelet initiation and heading was also significantly affected by photoperiod, but its magnitude was different amongst cultivars. Sunsetaw showed a simple quantitative trend, while Condor and Rosella, which also had quantitative responses, responded in a more complex fashion with a much stronger sensitivity to very short photoperiods (< 12 h, Ps2) than to longer photoperiods (Ps). Cappelle Desprez had a qualitative response for very short photoperiods. It was concluded that (i) differences among cultivars in response to . photoperiod can be conveniently partitioned into different parameters for describing photoperiodic sensitivity, (ii) these parameters appear to be unrelated, allowing for speculation that plant breeders could manipulate them independently for customising cultivars for particular environments, (iii) the parameters were sensitive to temperature, suggesting that it would be inappropriate to extrapolate the response to photoperiod from one thermal environment to another, and (iv) the length of the late reproductive phase from terminal spikelet initiation to heading was not only significantly affected by photoperiod, but was even more sensitive to photoperiod than the early phase to double ridge. This thesis concludes with a chapter that discusses the relationships between the results from individual studies and identifies avenues for future work.
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ItemEffect of lupins on the performance of young calves( 1994)This study was conducted to examine the performance of young calves early weaned off milk replacer and fed on starter concentrates containing 0% to 100% lupins. Thirty male Friesian calves aged up to one week old were involved in the experiment. Due to the outbreak of scours, 4 calves died prior to the actual start of measuring at week 4. The rest were allocated at random based on stratified liveweight to 4 treatment diets containing 0, 33, 67 and 100% steamed-flaked lupins fed ad libitum during 28 days of period 1 (preweaning) and 35 days of period 2 (post-weaning). Calves fed 100% lupins completely lost appetite and grew slowly after 6 weeks of receiving experimental diet although the reason for that was not fully elucidated. However, including lupins up to 67% in diets of young calves did not affect the health status, feed intakes, feed efficiency and growth rates (P>0.05). Calves fed diets containing 0, 33, and 67% lupins consumed about 2.5 kg DM/day and grew at approximately 1 kg/day with feed conversion ratios of approximately 2.5 kgDM/kg liveweight gain during the post-weaning period. Plasma and ruminal metabolic measurements were fairly uniform (P>0.05) for these calves indicating they had similar degrees of ruminal development and fermentation. Digestibility of DM, N and NDF decreased (P<0.05) with the increase in proportion of lupins in diets whereas that of ADF showed no significant (P>0.05) difference among treatment diets. The result indicated that steamed-flaked lupins can be satisfactorily included up to 67% in calf starter rations without adverse effect on calf performance. Including lupins at these levels helped cut the feed cost per unit gain weight by 10% compared with using 100% commercial calf pellets.
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ItemGrowth and yield of rice cultivars of differing growth duration in New South Wales( 1993)The growing season for rice in New South Wales is limited by low temperatures in Spring and Autumn. With current cultivars, almost all of the possible growing season is used in producing a crop. Cultivars with short growth duration have been sought by rice growers in southern New South Wales for reasons of decreased water use, increased flexibility in designing rotations and added time for rice field preparation in the event of a wet spring. This study examines the growth and yield of a short-duration cultivar compared with commercial long-duration cultivars, when subjected to a range of fertiliser applications and sowing times. Biomass accumulation of the short-duration cultivar was smaller than that of the long-duration cultivars, however yield potential was similar. This was achieved by the production of similar number of florets/m2 despite smaller biomass at flowering, and greater harvest index. Early sowing resulted in smaller yield due to restricted biomass accumulation and floret production of the short-duration cultivar. The short-duration cultivar had a greater proportion of filled grains and thus yielded more than the other cultivars when sown late. While yield of all cultivars was reduced with late sowing, the short-duration cultivar was affected least. Cultivars of this type are therefore recommended when late-sowing is unavoidable. Variation in yield was not due entirely to low-temperature damage at the critical growth stages of pollen microspore development and anthesis. Yield was also associated with growth after anthesis. A summary model of post-anthesis growth, which included the effect of low temperature on growth, predicted growth with an accuracy similar to that of the growth measurements. Thus, in determining yield, the importance of environmental conditions during grain filling was highlighted. It was concluded that the yield of short-duration cultivars may be less stable when stress occurs during grain filling, because there is less reserve available to fill the grain. Continued work on short-duration cultivars is advocated, with emphasis on faster growth to provide greater biomass production in the shorter vegetative stage. Incorporation of tolerance to low temperatures during the grain-filling stage is also suggested, to give greater yield stability.
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ItemRoot-shoot interactions in the growth of irrigated white clover( 1993)White clover pastures support the dairy industry in the irrigated area of northern Victoria. However, pasture production is low because conditions for root growth are sub-optimal, particularly under flood irrigation. This thesis investigated the possibility that the growth of white clover can be increased by reducing the limitations to root growth. A series of experiments examined the response of white clover plants to various soil-based treatments and quantified relationships between root and shoot growth. Plants were grown in intact soil cores in the greenhouse with shoot and root growth measured by destructive harvest. The cores were collected from a range of field sites that were characterised by their different soil physical properties and the variation in pasture yield they supported. Other cores contained a sand-based potting mix in which the conditions for root growth were superior to the most productive field soil. Despite the large effects of soil treatment on white clover production, the growth of shoots and roots was highly correlated (R2>0.95). A prerequisite of high shoot yield is, therefore, a large root system. In one experiment, soil drying or defoliation perturbed the correlation but this disruption was only temporary. In another,experiment, the repeated cycles of drought stress that accompanied a series of extended irrigation intervals had no effect on the relationships between shoot and root growth. In field soils, the restrictions to root growth could not be overcome by intensive irrigation and fertiliser management. However, plants in the treatments in which the soil physical properties had been modified produced 4.0 - 6.5 times as much shoot DM compared with the least productive treatment. This suggests that the potential to improve pasture yield by amelioration of the soil physical properties is very large. Two further experiments were conducted in which either the soil texture or the frequency of irrigation varied between the upper and lower sections of the soil cores. In both cases the production of shoots was correlated with total root production. However, when `unfavourable' conditions restricted the growth of roots in one layer, extra growth of roots in the `favourable' layer was not sufficient to compensate. As a consequence, both total root and shoot growth were reduced. Taken together, these results suggest that there is a large scope to improve the yield of white clover by removing the restrictions to root growth that currently exist in field soils. This will probably entail both amelioration of the soil physical properties and careful management with respect to water and fertiliser applications. However, if the experiments reported here accurately reflect the field situation, then the growth of white clover pastures can only be maximised if the entire root zone is modified.