Agriculture and Food Systems - Theses
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ItemA study of weight-loss and compensatory gain in sheep( 1971)Two experiments of similar nature were conducted. In the first experiment 49 Corriedale wethers at approximately 8 months of age were allocated to four experimental groups and, within groups, to various slaughter weights which were spaced at 5 kg intervals. Group I animals were fed ad libitum and slaughtered - over a body weight- range of 38 - 63 kg inclusive. Groups II and III animals were fed ad libitum until 48 kg body weight hereupon intake was restricted to achieve a body weight loss of 0.9 kg/week until body weights were reduced to 38.5 kg and 34.5 kg, respectively. Ad libitum feeding was then resumed and animals were slaughtered up to 63 kg body weight at the same weight intervals as in Group I. Group IV animals were fed ad libitum until 48 kg body weight and then, food was adjusted to maintain body weight at 48 kg. Four animals were slaughtered after 60 days and a further four after 120 days of maintenance of body weight. In the second experiment, 15 wethers of similar age, breed and nutritional history as those used in Experiment 1, were allocated to four slaughter groups in a treatment similar to that of Group III in Experiment 1. Four animals were slaughtered at 33 kg body weight at the beginning of the first period of ad libitum feeding; three animals slaughtered at 45.5 kg at the end of the first period of ad libitum feeding; three animals slaughtered at 33.5 kg at the end of the weight loss phase; and five animals slaughtered at 46.5 kg at the end of the second period of ad libitum feeding. The compensatory growth rates of animals in Groups II and III were greater than those of Group I in each of the successive 5.5 kg increments in body weight. By maintaining higher growth rates over the entire weight range, the largest animals of Groups I I and III were slaughtered at a similar age to those, of Group I. Similarly, in Experiment 2, the compensatory growth rates (Group VI) were greater than continuous growth rates (Group V) over the body weight range used in this experiment. The data was transformed to logarithms in order to use Huxley's (1932) allometric growth equation in the linear form for an analysis of covariance. During continuous growth (Groups I and V), the empty body weight (EBW) increased as a proportion of full body weight (FEW) whilst during the compensatory growth which followed weight loss (Groups II, III and VI) the proportion of EBW remained constant. At the same FEW the EBW of Groups I I and III was less than that of Group I. Similarly, the EBW of animals maintained at a constant body weight (Group IV) was less, at the same FBW, than that of Group I. Carcass weight (CW) increased as a proportion of EBW as EBW increased in Groups I and V but the proportion remained constant in Groups II, III and VI. At the geometric mean FEW, treatment did not affect CW. However, the apparent dressing percentage (CW / FBW x 100) was 2% less during compensatory growth compared with that during continuous growth. The carcass length of animals in Groups II, III and IV was greater than that of animals in Group I.
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ItemThe physical and functional development of the forestomachs of the lamb( 1960)In this thesis a study of the physical and functional development of the forestomachs of the lamb is presented. The experimental work can be divided into three main fields as follows:- a) Studies on the physical development of the fore- stomachs. b) Studies on the functional development of the reticule-rumen. a) Field work in which the above studies have some direct bearing. The main findings of these studies have a) PhysicaI development of the forestomachs: In grazing lefts the four stomachs have reached their adult proportions by approximately 8 weeks of age. The type of diet can markedly influence the rate of growth of the forestomachs, and in general, it would appear that plant food is needed for the normal development of the forestomachs, and It plant food is excluded from the diet the development of the forestomachs is retarded at about the level found in the 3 week old grazing lamb. The main changes in the histology of the forestomach walls takes place during the last third of foetal life, and the adult his histological features are all present at birth. The major post-natal histological changes are complete by 56 days of age. It would appear that age is the main factor controlling the histological development of the forestomachs, and that plant material is necessary for the full development It of these organs. It was also shown that different diets can cause differences in the appearance of the rumen mucosal surface, stratum granulosum and stratum corneum. b) Funcational development of the reticulo-rumen: It was postulated that the functional development of the reticulo-rumen of the grazing iamb could be divided into three phases - a non ruminant phase (0 - 3 weeks of age), a transition phase (3 - 8 weeks of age) and an adult ruminant phase (8 weeks of age onwards). If plant food was excluded from the diet, the lamb remained in the non- ruminant phase, however, once plant food was fed to these lambs the reticule-rumen function reached the adult levels within one week. c) Field studies: As the forestomachs of the grazing are qualitatively and quantitatively fully developed by approximately 8 weeks of age, it is possible to ween lambs of this age with no check to their growth rate, provided the pastures are relatively high in protein and are not at the late flowering or seeding stages. The milk yield of the grazing ewe measured by the oxytocin technique gave consistently higher recordings throughout Iactation than the conventional lamb suckling technique. By the tenth week of the lactation the milk yield, as measured by both techniques, had fallen by half. There was a high correlation between the milk yield of the ewe and the lamb live weight growth up to seven weeks of age.
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ItemStudies in animal nutrition : the intake and storage of dietary nitrogen and energy( 1963)This thesis is divided into two parts. Part I consists of three chapters. Chapter 1 is a critical review of the literature which deals with the nutritional factors which influence nitrogen and energy retention in animals. In the light of these factors, the effect of dietary composition on the relative storage of energy as fat and protein is discussed. The review concludes by discussing the effect of energy storage as fat and protein on changes in liveweight. There is an extremely large volume of literature on this subject and no attempt has been made to cover it exhaustively. The more important contributions to the field have been mentioned and the review investigates the variety and complexity of nutritional factors which may influence the composition of energy storage, and discusses their likely effects. Chapter 2 describes two experiments where four diets, which differed in their levels of protein, were each fed at four levels of intake to adult guinea pigs. The effect of the level of dietary protein on the energy and nitrogen balance of the animals was investigated. Chapter 3 reports an experiment in which the change in liveweight of penned sheep, fed diets which varied in the levels of protein and energy, was interpreted in terms of the nitrogen balance of the animals and their metabolizable energy intake. The contents of Chapters 2 and 3 are to be submitted for publication shortly. Part II of the thesis consists of four published papers dealing with the food intake of grazing sheep. Chronologically the work reported in Part II preceded that reported in Part I. Chapter 4 and 5 deal with the faecal-nitrogen technique for measuring the intake of grazing sheep for both annual and perennial pastures. Chapter 6 reports the results obtained when faecal-nitrogen techniques were used to estimate the intake of a group of grazing sheep and Chapter 7 uses the results of Chapters 5 and 6 to present a hypothetical model which suggests the importance of dietary composition, with respect to digestible organic matter and digestible nitrogen, in determining the liveweight change of sheep grazing annual pastures.
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ItemThe reactions and availability of manganese in soils( 1969)The reactions of Mn in soils and the relationships between these reactions and the mechanisms of supply of Mn to plants have received attention from scientists over the last 40 years; most attention being given to the problem of Mn deficiency which occurs most commonly in soils with pH's from 6.5 to 8.0. The term "neutral" soils will be used throughout this thesis for these soils on which in deficiency occurs; the term is just as meaningful as and less cumbersome than the term "neutral and alkaline soils" which is commonly used. Some significant contributions have been made to our knowledge of the availability of In in neutral soils, but the progress has been unduly slow. It would appear that the slow progress can be partly attributed to the perpetuation of poor work, and thinking, not only by some workers in the subject, but by some writers of textbooks. This is a serious allegation to make, but when one becomes intimately involved in the subject, one is confronted with many pieces of work which are incompatible and mutually contradictory. The commonly accepted reason for In deficiency is the microbial oxidation of divalent In to higher in oxides, and yet many workers are obviously not aware of evidence which makes this conventional theory look absurd. The two simple facts that microbial oxidation of divalent Mn occurs in all neutral soils and that Mn deficiency is a "disease" of the wetter and cooler climates of the world illustrate my point precisely. This unsatisfactory situation calls for a critical appraisal of the existing theories, and in this thesis I have attempted to do this and to give a clear account of the subject. The reader will quickly find, however, that here we have a very complicated problem to which we only know some of the answers. In this thesis reference is made to some "local" soils, namely: Corny Point, Dooen, Hallam, Mt. Gambier, Penola Hill, Penola Flat, Rendelsham, University, Walpeup, Werribee, and Yambuk. And, for the convenience of the reader, some of the relevant properties of these soils are described in Part IV - Experimental Methods and Description of Soils, pp.252-255. The Introduction is not a complete review of all the work which has been done on Mn in soils. It is deliberately selective and obviously some work is irrelevant here, but some other work has been omitted either because it is mere duplication or because it does not warrant perpetuation; though possibly some work, which is relevant or otherwise, may have been overlooked. The early part of the Introduction outlines our present knowledge of the reactions and availability of in in neutral soils. This is followed by an attempt to define the nature of the root surface, a subject which has received little attention in relation to soils and has considerable relevance in the mechanism of uptake of in from neutral soils. The experimental work covers several aspects of Mn in soils, namely: the microbial oxidation of Nn, the reversion of available forms of in and the uptake of Mn by contact reduction. The results and discussions of the experiments indicate forcefully the extreme complexity of the problem of the availability of In in neutral soils. And, possibly just as important, they indicate that in a few years, one person cannot possibly solve a problem which has been baffling scientists for decades.
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ItemGrowth, body composition and related studies of farm animals( 1975)The publications included in this thesis report experiments done while the candidate has been a member of staff at the University of Melbourne (1957-1975) . The thesis is divided in five sections, as follows:- (Paper Nos.) Growth and development of farm animals 1-20. Physical studies of the alimentary tract of dairy cattle 21-24. Investigations of the skin of cattle 25-27. Animal behaviour 28-29. Miscellaneous papers on animal production 30-33. The section entitled "Growth and Development of Farm Animals" begins with a review (Paper No. 1) of the results of some of the papers in this section. It is followed by two papers (2, 3) which re-analyse the data of other authors and present hypotheses which are later developed and tested (in papers 4 to 20) . Papers numbered 4, 7, 25, 26, 27, 28, 29 were presented as part of the candidate's Ph.D. thesis. They are included, not for examination, but because they are related to other work in this thesis. Papers numbered 2, 3, 5 are related to material in the same Ph.D. thesis. In all papers where authorship is shared, the joint authors were either scientific colleagues, research assistants or graduate students. In all cases, the candidate made a contribution in the collection of the data, and was responsible for the design of the experiments. He was also responsible for the supervision of the work and played a major role in preparing it for publication. Where the candidate's name appears either as sole author or as senior author, he was directly responsible for and involved in all aspects of each experiment.
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ItemResearch in plant virology( 1965)
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ItemEpidemiological and physiological studies of the effects of peach rosette and decline disease on the peach, prunus persicae L. Batsch( 1975)The incidence in the field of the disease peach rosette and decline (PRD), which is of considerable economic importance in the Goulburn Valley, causing fruit loss and tree death, was shown to increase from 0.9 to 91.3% in an orchard of cv. Golden Queen in 10 years. Similar results were found with the cv. Pullars Cling, in which infection increased from 1.5 to 29.7% over five years. The pattern of spread was mainly from infected trees to contiguous uninfected trees. This is consistent with the view that the main causal agent, prune dwarf virus (PDV), is transmitted only via the transfer of infected pollen : a previous finding in cherries which was confirmed in peaches. Prunus necrotic ringspot virus (PNRV) is the other virus always present in the field in PRD-infected trees. The mode of spread of PNRV is also by pollen. Within the tree, PDV moved erratically from the first infected limb, via phloem but not xylem, into the other limbs well in advance of the appearance of symptoms. Three months after flowering, PDV was detected in 65% of main limbs adjacent to the first infected limbs but in only 30% of limbs more remotely positioned on the tree. However, removing infected limbs within four weeks of flowering, when the initial infection was presumed to have occurred, did not prevent the movement of PDV into the rest of the tree. Laterals from peach trees infected with PRD were tested for the presence of PDV, using woody virus indicators (cvs Golden Queen, Italian Prune and Elberta seedling). Golden Queen was found to be a more reliable indicator for detecting PDV than Italian prune, as the presence of PNRV with PDV killed 71% of the Italian prune buds compared to only 34% of the Golden Queen buds. Golden Queen also developed more obvious foliage symptoms of PDV infection than Elberta seedlings. The probability of failing to detect PDV in infected field trees, using all three indicator plants, was higher in the first year of infection. The rate of spread of PRD was reduced in the orchard by preventing infected trees from flowering, either by removing obviously infected trees or by deblossoming. Removing infected trees resulted in a three-fold reduction in the spread of the disease in two seasons. Removing the flowers from infected trees before pollination reduced the spread of the disease by about half. This, only partial, control of the spread of PRD by tree removal or deblossoming was attributed to the presence of up to 14.3% of trees without symptoms being latently infected with PDV. It was observed that deliberate infection with PDV by pollen also resulted in a slow expression of the symptoms of PRD. The effects of PRD on the growth of young peach trees was obvious in the first three months of growth. There were considerable varietal differences in the severity of this effect. Those varieties based on cvs. Golden Queen or Levis Cling were more severely affected than the variety Elberta. The results from shoot elongation measurements agreed with those obtained from conventional growth analysis methods. These latter experiments showed that, after three months, the dry weight and leaf area of infected Golden Queen plants were reduced by 94%. The fruit yield from mature PRD-free trees was three times that of trees infected for the first season, even though symptoms were apparent only on one limb; and six times that from chronically affected trees infected for two seasons. The effect of virus infection on the photosynthetic ability of single, attached peach leaves was studied under laboratory conditions using infra red gas analysis. The constants derived from the equations describing the relationship between net photosynthesis (Pn) and both irradiance and CO2 concentration were used to analyse the effects of infection by PRD on photosynthetic characteristics of the leaf. The asymptotic value of Pn (Pmax) in young leaves was reduced 15% by PRD-infection, mainly through an increase in the "residual resistance" to 002 diffusion and a decrease of 23% in the parameter indicating photochemical efficiency. There was also evidence that the gas phase resistance was higher in infected leaves at low levels of irradiance. Dark respiration was 51% higher in infected leaves, but this difference was not significant. PRD did not reduce Pn in 60-day-old leaves, normal leaf senescence having a predominant and greater effect. It was concluded that PRD infection had its large effects on growth via a reduction in leaf area; the effects on the photosynthetic capacity per unit leaf area being minor. An effect of PRD infection on the translocation of 14C-assimilatesout of leaves was also observed. Infected leaves retained twice the assimilates than did uninfected leaves. It is concluded that the most promising methods of control of PRD include removal of infected trees, deblossoming suspected infected trees until diagnosis is confirmed, use of virus-tested plants, the gradual destruction of infected orchards and protecting young, healthy orchards from infection either by barrier crops or deblossoming the young plants until they reach an economic bearing age.
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