School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemNo Preview AvailableTribes and territories : aspects of Aboriginal political geography in the Northern Territory of Australia(University of Melbourne, 1989)
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ItemStudies of the preovulatory LH surge and ovulation in the ewe( 1989)The studies presented in this thesis addressed the hypothesis that the induction of the preovulatory LH surge and ovulation in the ewe involves changes in the pattern of GnRH and gonadotrophin secretion, which can be compromised by the effects of glucocorticoids from the adrenal gland. A series of experiments tested the hypothesis that administration of exogenous GnRH or gonadotrophins could induce the growth of follicles to the point of ovulation in ewes deficient in endogenous gonadotrophins. A number of regimes were tested in hypophysectomized ewes where the timing, dose and type of exogenous gonadotrophin varied, but none of these could elicit ovulations consistently. When one of these regimes was administered to hypothalamic-pituitary disconnected (HPD) ewes, a greater response was obtained (33% of ewes ovulating versus 4% in hypophysectomized ewes). Administration of exogenous pulses of GnRH was able to elicit ovulations in HPD ewes consistently (88% of ewes ovulated). These findings imply that a pituitary factor besides the gonadotrophins may be important for the normal growth and ovulation of follicles. In another group of experiments, exogenous regimes of GnRH were administered to ovariectomized HPD ewes to test whether modifications in GnRH input could effect changes in LH secretion during an oestrogeninduced LH surge. It was found that `signal' pulses of GnRH, as either a single large pulse or a rapid series of smaller pulses, were required to initiate an LH surge in the presence of oestrogen. These `signal' pulses of GnRH were unable to cause a similar surge of LH in the absence of oestrogen. A continuous infusion of 250 ng/hour GnRH decreased the magnitude of the oestrogen-induced LH surge compared to 250 ng pulses of GnRH, but elicited a significantly greater response than if GnRH input was abolished, suggesting that the basal secretion of GnRH as well as the pulsatile format was important in eliciting an LH surge. When the continuous infusion was doubled to 500 ng/hour, this treatment was as effective as the 250 ng pulses of GnRH, whereas decreasing the GnRH pulse amplitude from 250 ng to 125 ng had no effect. These findings suggest that an increased baseline level of GnRH secretion can overcome the lack of pulsatile input, and that within the range tested, the amplitude of the GnRH pulses is not critical during the oestrogeninduced LH surge. Removal of GnRH inputs following the initiation of the oestrogen-induced LH surge significantly decreased in the amount of LH secreted compared to when GnRH pulses were maintained, showing that GnRH input to the pituitary gland is still required once the LH surge has begun. To investigate the hypothesis that gonadotrophin subunit mRNA levels are dynamic during an oestrogen-induced LH surge, ovariectomized and ovariectomized HPD ewes were treated with oestrogen and sacrificed at various times during the short-term negative and positive feedback events. In the ovariectomized ewes, all gonadotrophin mRNA levels decreased progressively, with LH/3 mRNA levels being significantly less than control values by the onset of the LH surge, whereas FSH/3 and a subunit mRNA levels declined significantly during the LH surge. These findings are at variance with those reported for ovary-intact ewes, suggesting that the mechanisms responsible for the LH surge in ovariectomized ewes treated with oestrogen may be different from those involved in the preovulatory LH surge. In the ovariectomized HPD ewes, the levels of a subunit mRNA levels diminished after treatment with oestrogen, whereas the levels of LHJ3 and FSH/3 mRNA levels were unchanged, implying that the a and f3 gonadotrophin subunits may be differentially regulated. Another series of experiments investigated the hypothesis that the synthetic glucocorticoid, dexamethasone, modified reproductive function. Chronic administration of dexamethasone at rates of up to 2 mg/day had little or no effect on gonadotrophin secretion, the incidence of behavioural oestrus or ovulation rate in either the breeding or non-breeding seasons. Based on these findings, it was revealed that in the ewe, the induction of the preovulatory LH surge involves changes in the pattern of GnRH and gonadotrophin secretion, but that glucocorticoids from the adrenal gland have, at most, only a minor role in modulating these processes.
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ItemGrowth of Pinus radiata (D.Don) stands in relation to intra- and inter-specific competition( 1989)This study investigated the growth of even-aged Pinus radiata stands in relation to intra-specific and inter-specific competition. The first part of the thesis used a data set of 30 year experiments together with a glasshouse experiment. A maximum stand biomass-density line was estimated for the P. radiata stands undergoing self-thinning. This line constrained the stand biomass-density trajectories of the individual stands. Growing along the trajectories, most stands increased the skewness of tree size distribution and the size hierarchy of the population. This was closely related to competitive status-dependent growth and death of trees in the stands. Height/diameter ratio decreased with competitive status. The relationship between them did not change significantly during stand growth. The experiment with P. radiata seedlings implied that competition for light was relatively important in affecting the growth, allocation and allometry of P. radiata during intra-specific competition. The second part of the thesis studied a 10 year old P. radiata plantation invaded by Eucalyptus obliqua. The study was done in conjunction with a replacement experiment with P. radiata and Eucalyptus regnans seedlings. The experiment revealed that P. radiata was more aggressive towards Eucalyptus regnans at the seedling stage. In P. radiata stands invaded by E. obliqua, the size and stem form of P. radiata was closely related to the polygon area defined by its by' E. obliqua neighbours. As the density of E. obliqua increased, its rooting density also increased. This related closely to the decrease in (1) rooting density, (2) aboveground tree size, (3) total projected leaf area, (4) total stem volume and to the increase in the skewness of size distribution and the size hierarchy of the P. radiata populations. The results suggested that competition for water and nutrients was relatively important for P. radiata in competition with E. obliqua in these stands.
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ItemInterregional trade in sawntimber in Australia( 1989)The purpose of this study has been to develop a modelling framework which incorporates the essential features of the sawntimber market in Australia and which is capable of being used to study both the interregional trade patterns within Australia and the impacts of various changes on the sector. This firstly involved the determination of demand and supply relationships for the market and secondly the development of a spatial equilibrium model of trade. The basic structure of sawntimber market was studied with the use of two different approaches. The first was an ad hoc, statistical model of the sawntimber market in Australia. The statistical model provided new results for price elasticity of sawntimber demand in Australia. Elasticity of demand for sawntimber was found to be -0.783, an improvement on previous studies which found no relationship between sawntimber demand and the price of sawntimber. It also provided new information on the structure of the sawntimber market in Australia and the substitution between imported and domestic supplies. In particular, the results showed that domestic and imported sawntimber do not compete on the basis of price in the Australian Market. The second approach was through a theoretical model of the production structure of the sawmilling industry using the translog cost function. The estimation of the cost function served two purposes, the first to provide a measure of the slope of the supply curve for the trade model, and the second to provide information about the production structure of the industry. Although .data problems ultimately prevented the use of the translog cost function in the spatial equilibrium model, it did provide new information on input substitution, technological change and scale economies in the sawmilling sector. In particular, the results found that most inputs are substitutes, there are diseconomies of scale, and that technological change has been capital and energy using, and labour saving. The second component of the study was the development of a spatial equilibrium model of the sawntimber sector. This was done with a non-linear programming framework and based on demand and supply elasticities provided by the statistical model. The result was a model which could be used to study the impacts of demand and supply changes. The model was used to study the impact of the forecast increase in log availability by the year 2000. An important result from the use of this model was to demonstrate that an 11.5 percent price decrease could cause the domestic market to absorb 60 percent of the sawntimber which the increased log availability could allow. To summarise, the research encompassed in this thesis has provided new information on the economic structure and performance of the sawntimber sector in Australia. It has also provided a basis for new research and applications of the results. In this study the results were applied to a spatial equilibrium trade model of the sector in Australia. This in turn has provided a new basis for policy analysis in forest industry, in particular issues involving trade and demand or supply shocks.
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ItemThe activity of glyphosate and other herbicides in soil( 1989)The effects of herbicides on a legume Rhizobium symbiosis were studied in laboratory experiments. Root applications of all herbicides examined reduced nodulation of legumes grown in aqueous nutrient media. The growth of Rhizobium trifolii TA1 was reduced by 2 - 20 mg ai 1-1 of diquat, 2 mg ai 1-1 of paraquat, 10 mg ai 14 of glyphosate and 2 mg ail-1 of chlorsulfuron. No other herbicide affected rhizobia growth when applied at 2 - 20 mg ai l-1 of nutrient medium. Inoculation with TA1 pre-treated with amitrole, atrazine or glyphosate decreased nodulation of sub-clover plants indicating that these herbicides may affect the nodulation potential of certain strains of Rhizobium. Residues of 2,4-D, amitrole, diquat, trifluralin and glyphosate persisted in a Walpeup sandy loam in sufficient concentration for four months after application to soil to affect growth and symbiotic activity of sub-clover. The behaviour of glyphosate in soil, under various conditions was studied in the laboratory. Adsorption of glyphosate as depicted by Freundlich K constant was greater in an acid soil than in three alkaline soils and values for this constant ranged from 8 - 67.8 at 23.5C and 4.3 - 57.8 at 10C. Rate of decomposition of 14C-glyphosate at 25C decreased slowly over the experimental period in all soils. Two compartments of adsorbed glyphosate in soil were identified as labile glyphosate and non-labile glyphosate and these reflected the strength of adsorption of the chemical. The amount of glyphosate in the labile firm for the soils ranged from 24 - 34.5% of the total and half-life ranged from 6 - 9 days. The amount of glyphosate in the non-labile form for soils ranged from 67 . 75% of the total and half-life ranged from 222 to 835 days. At 10C, the two compartments of glyphosate adsorption were identified for the Walpeup and Rutherglen soils but only one compartment could be identified in the Wimmera and Culgoa soils. Methodology was developed to permit extraction and analysis of glyphosate and AMPA in soil. Recovery of glyphosate from soils where time between fortification and extraction was only 30 sec. was 84.6 - 104%. However where extraction was delayed 13 hours, recoveries were 47.6 - 66.8%. The extractant (0.1 M triethylamine) was shown to be unable to desorb adsorbed glyphosate. Studies revealed that at 25C, the pool of extractable glyphosate was rapidly depleted by decomposition. At this temperature, the pool of extractable glyphosate was supplemented by slow desorption of non-labile glyphosate for each soil. At 10C, depletion of the pool of extractable glyphosate was considerably slower. For the Walpeup and Rutherglen soils, the rate of desorption of glyphosate from the non-labile pool was less than the rate of loss by decomposition of the herbicide. Rate of desorption of non-labile glyphosate in the Wimmera soil was shown to be the same as the rate of loss by decomposition of the herbicide. Loss of extractable glyphosate in the Culgoa soil occurred by decomposition and by slow adsorption of extractable herbicide from the labile to the non-labile form. The effects of residues of glyphosate in the field following an autumn and a summer application were investigated at selected field sites. Following the autumn application, phytotoxic activity of glyphosate was observed in sub-clover plants growing at the Walpeup and Culgoa sites but not at the Wimmera site. Growth and nodulation of plants sown up to 4 weeks after herbicide treatment were reduced at the Walpeup site. Only nodulation of plants sown up to 4 weeks after treatment was reduced at the Culgoa site. Results suggest that residues of glyphosate are only likely to significantly affect the growth of susceptible plants during winter on sandy soils. Following summer application of glyphosate, no phytotoxic activity of the herbicide was observed for sub-clover plants grown in the Walpeup sandy loam. Results suggest that in a hot summer, it is unlikely that residues of glyphosate in any soil would cause significant damage to plant growth.
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ItemThe nutrition of multiple-bearing ewes in late pregnancy( 1989)The nutrition of multiple-bearing ewes in late pregnancy and relationships with lamb survival are reviewed (Chapter 1). The frequent reductions in voluntary intake in late pregnancy, the reliance on maternal reserves and the key role of glucose and protein are highlighted. The sensitivity to nutritional manipulation of traits associated with lamb survival and their variation due to litter size are discussed. The traits include lamb birth weight, lamb vigour, ewe mammary growth and colostrum production, maternal behaviour and gestation length. A hypothesis 'That short-term supplementation of multiple-bearing ewes late in pregnancy will improve responses associated with lamb survival' was developed. Supplementing prolific ewes with lupin grain for the final 10 days of pregnancy has previously significantly increased lamb survival rates (Chapter 2). Experiments were designed to test the hypothesis. Treatments included supplements of different grains, nitrogen or rumen undegradable protein and direct infusions of glucose. Responses measured included production traits associated with lamb survival, glucose, urea and fatty acid production rates, some hormone concentrations, voluntary feed intake and mobilisation of maternal reserves. The variation in responses was compared at various litter sizes. Treatments were selected so that results could be modified and then applied directly to grazing sheep in southern Australia. In the first experiment (Chapter 3) a lupin grain supplement fed to Booroola (prolific) ewes in the final 17 days of pregnancy reduced condition score losses compared to no supplement or an oat grain supplement. -Live weight gains were highest with the lupin supplement and with no supplement. There was a trend for milk production at day two post-partum to be higher with the lupin supplement. Some of the multiple-born lambs died because of low colostrum intake, as indicated by low serum immunoglobulin concentrations. The possible importance of colostrum and initial milk production was demonstrated. Colostrum production and milk production on day one and nine were similar from single and multiple-bearing ewes fed a ration containing 100 g protein/10 MJ metabolizable energy and this ration supplemented with formaldehyde-protected casein or urea (Chapter 4). The ration was fed at 90% of the average estimated requirements of all ewes in the final five weeks of pregnancy. Gestation length was two days shorter with the casein supplemented diet which resulted in twin-born lambs from this diet being about 14% lighter than lambs born to ewes fed the basal ration. Glucose production on day 121 was 32% higher with multiple than single-bearing ewes even though intakes were comparable. Many ewes had low voluntary intakes on the grain/roughage ration and this resulted in large energy deficits. On a roughage/ oat grain ration fed for the final seven weeks of gestation, single and multiple-bearing ewes had consistently low and equivalent intakes (Chapter 5). Nonesterified fatty acid production rates on day 115 and 136 averaged 65 % higher for multiple than single-bearing ewes and rates were similar on both days. Glucose production increased by 32 % between these days and was 17 % greater for multiple than single-bearing ewes. The correlation coefficient of fatty acid and glucose production rates was about 0.7 on both days of measurement. The provision of a large glucose source late in pregnancy may be beneficial to multiple-bearing ewes when their voluntary intake potential seems low. Multiple-bearing ewes were infused at the abomasum from day 119 to 145 of gestation with nil, 106 or 207 g glucose /day (Chapter 6). The glucose was estimated to provide an additional 20 or 40 % energy compared to the basal ration of lucerne chaff. The ewes which were infused with glucose gained more weight during the treatment period (90, 159 and 267 g/d for basal, +20% and +40% energy respectively). Litter weight, colostrum yield and early milk production were insensitive to additional energy, as glucose, in the last 30 days of pregnancy in the circumstances where ewes were in low condition and fed a restricted roughage ration containing a high percentage of protein. The insensitivity seemed to lie with increased insulin levels leading to peripheral tissue accretion. Again high variation occurred in colostrum yields, although amounts were higher than in previous experiments. There were significant positive correlations between litter weight and both progesterone and plasma ovine placental lactogen levels in late pregnancy. Colostrum production was negatively correlated to progesterone concentrations measured in late pregnancy. Intake declined close to parturition even with the glucose infused ewes. When ewes were fed a medium quality roughage ad libitum, a lupin supplement in the final 10 days of pregnancy increased colostrum yield by 37% and milk production on day 1 by 28% when averaged over all ewes (Chapter 9). The largest response occurred with the triplet-bearing ewes, which had much lower production than single and twin-bearing ewes. Lambs born to lupin supplemented ewes had faster growth rates to day 1 and 3 post-partum. Benefits occurred either through additional substrates and /or by changing hormonal status, specifically progesterone. Colostrum levels at birth and total milk production to 24 hours were significantly improved when multiple-bearing ewes were supplied with supplements of glucose, lupin grain or undegradable rumen protein in the final 10 days of pregnancy. The basal ration was a medium quality roughage fed at a restricted level. The results provided strong evidence that additional protein which escapes rumen degradation will increase colostrum production near birth and advance the timing of copious milk production. The colostrum and milk yields were negatively correlated to progesterone concentrations near parturition. Prolactin and ovine placental lactogen concentrations measured before and after parturition were poorly correlated with the lactation results. Triplet bearing ewes had lower milk production than twin bearing ewes. There were no effects of the treatments on birth weight, but large effects on ewe live weight change and gestation length. The mechanisms could be due to extra fat mobilisation in late pregnancy with additional protein supplies, changes in hormone status, or possibly the supply of extra amino acids compared to the non-protein treatments. Variability in the colostrum and milk responses on the glucose treatment made it unclear what the role of glucose was for colostrum production. Milk production of multiple-bearing ewes is likely to be below that required by their litter in a cold and wet environment in the first 24 hours when the ewes are fed a medium quality roughage diet (Chapters 7 and 10). Lambs had a potential colostrum intake in the first two hours of an average 110 g and 230 g/kg birth weight during the first day (Chapter 8). This amount was usually above that available to all lambs in the litter from the dam. The potential intake was also above that required in most environments. Limited variation in intake between lambs within a litter may be crucial to survival of the complete litter. It is proposed that protein has a specific effect on the endocrinology of the ewe in late pregnancy. Thus a possible hypothesis consistent with these data is that increased amino acid supply at the tissue level results in a faster clearance of progesterone allowing lactogenic hormones and hormones involved with the initiation of parturition to act. These experiments have thus demonstrated that short-term supplementation of ewes can influence some traits associated with lamb survival, including colostrum production at birth and milk production during the following 24 hours. Multiplebearing ewes will often have lower amounts of colostrum and early milk production than single bearing ewes. Supplementing ewes on medium quality protein/energy pastures with feed sources which provide a high protein yield at the small intestine should increase the initial lactation output and possibly survival rates of multiple-born lambs.
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ItemStudy of some aspects of elm root sucker growth (Ulmus x hollandica Mill.)( 1989)Elm suckers developed from root buds and/or bud primordia formed on root surfaces, and originated from pericyclic tissues beneath the periderm, and are therefore of endogenous origin. Elm root sucker formation was an auxin mediated process, and was related to the level of endogenous auxin at that particular time. Root segments suckered most in spring and least in autumn. Application of exogenous anti-auxin and cytokinin stimulated sucker formation from root segments in autumn, and application of auxin or growth inhibitors suppressed sucker formation in spring. The elongation rate of root suckers of elms decreased as the soil dried out and the soil penetrometer resistance increased. The effect of the soil drying out on increasing the soil penetrometer resistance was not in itself sufficient to account for the reduction in elongation rate as the soil dried. It was suggested that the reduction in soil unsaturated hydraulic conductivity (and the consequent reduced water uptake by the sucker) as the soil dried out was an additional reason for the reduced elongation rate. The osmotic potential of root suckers decreased as the soil dried out and as soil penetrometer resistance increased. In this instance, the effect of the soil drying out on increasing the soil penetrometer resistance was sufficient in itself to account for the reduction in osmotic potential (osmoregulation). As a consequence of this osmoregulation, turgor pressure either increased or was maintained at a constant value as the soil dried and as the soil penetrometer resistance was increased. The soil penetrometer resistance was found to be three times the value of the soil mechanical resistance to sucker growth. The net growth pressure (turgor pressure less soil mechanical resistance) decreased with soil penetrometer resistance. Sucker elongation rate increased with net growth pressure, but sucker elongation rate also increased with soil water content at constant net growth pressure. Elongation rate increased with time. Osmotic potential decreased; and turgor pressure and net growth pressure increased with time. The rate of decrease in osmotic potential and the rate of increase in turgor pressure and net growth pressure increased with soil penetrometer resistance, but this effect became less over time. The data suggest that elm root suckers can osmoregulate over time to reach a minimum value of osmotic potential (or maximum value of turgor pressure) which is independent of soil penetrometer resistance, but that the rate at which this minimum osmotic potential (maximum turgor pressure) is achieved increases with soil penetrometer resistance. Elm sucker elongation rate increased as the axis of elongation approached the geotropically preferred axis, ie the vertical upright position. Elm suckers exerted a maximum growth pressure of 0.63 MPa (SE=0.057) in a critical time of 5 to 6 days. Elm suckers exerted a buckling pressure of 0.34 MPa (SE=0.052) in a critical time of 24 to 30 hours. Elm suckers could not detect cracks or holes in a compacted soil by remote-sensing (ie no trematotropism in suckers). Root buds if pre-exposed to cracks had a better chance to develop into suckers than root buds not pre-exposed. Suckers preferentially selected growth pathways in the vertical upright direction provided no pores wider than 2mm existed in its way. If there were pores wider than 2mm diameter existed in its way, the sucker abandoned its vertical growth path preference and selected the wider pores instead even though the wider pores were set at an angle from the vertical.
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