School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemSome effects of botanical composition of pasture on the liveweight and wool production of sheep( 1972)Until recently, the main evidence on which to base pasture mixture. recommendations in Victoria, has been district experience and the results from dry matter ( "mowing") experiments. The grazing experiments described in this thesis, were initiated by Messrs. R. Twentyman, R. Newman, R. Allen and K. Maher of the Department of Agriculture during the period, 1960-196. Their aim was to develop some objective appreciation of the relative value for animal production of some of the sown and unsown species in Western district pastures. In addition to pasture species evaluation, they sought information on the relationship between pasture growth and animal production. Such information is needed so that Agrostologists can better evaluate the many pasture management factors (such as fertilizers, seeding rates, seed. treatments, herbicides, insecticides and defoliation treatments) that affect pasture growth and for which advice is frequently sought.
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ItemSupplementary feeding of slow growing lambs( 1976)Mount Derrimut Field Station, approximately 320 ha, is situated 22.4 kilometers to the west of the Melbourne General Post' Office. It is operated by the Faculty of Agriculture and Forestry of the University of Melbourne, primarily for undergraduate teaching in Agricultural Science but also as a Centre for research. The climate is of a Mediterranean type with an average annual rainfall of 450 min., mainly of winter incidence. Typically the growing season begins about mid August and finishes in late November to early December. Soils are of volcanic origin and are mildly leached, ranging from shallow stoney red loams on the slopes to. moderately deep grey clays on the flats. The pastures are generally of improved types although there are some native species particularly in those paddocks with large areas of rocky outcrops. The 290 ha, of land available for cropping and grazing carry a herd of thirty crossbred beef cows plus about fifty followers of various ages and a flock of 500 Corriedale breeding ewes. Each year about 60 ha, are sown to wheat, barley and oats. Selection in the sheep flock has primarily been directed towards the genetic improvement of wool quality and lambing percentages: less attention has been paid to the improvement of the lamb growth rates. Over the past ten years considerable difficulty has been experienced in growing the lambs to prime condition, suitable for slaughter, by the time the pastures have matured towards the end of the spring growing season. The ewes were mated during early March so that they would lamb in August when the spring flush was occurring. The lambs then had about three months in which to grow to slaughter weight before the pastures matured. In recent years, mating has been changed to mid January, so that lambing would occur during June and. July. It was anticipated that this early mating, although possibly having an adverse effect on lambing percentages, would' allow the lambs a further four weeks of growth before pasture maturity. The strategy of early mating has in part improved the numbers of lambs in prime condition at the end of the season but there is still a variable number of lambs that are not in prime condition at the normal sale time. These lambs must either be carried over into the dry summer and sold in the following autumn, or sold at the normal time as store lambs at a considerably lower price. In 1973 investigations were started in an attempt to develop management strategies that would reduce or eliminate the number of Underweight lambs by the time of pasture maturity. Preliminary studies in which all lambs in the Mt. Derrimut flock were weighed at birth and at subsequent six week intervals, suggested that lambs that were lightweight at pasture maturity were also lightweight at six weeks of age. The correlation coefficient between six. week weight and the subsequent length of time required to reach slaughter weight was found to be -0.60. Although the lightweight lambs had lower birth weights than the lambs achieving slaughter weight at the normal. time, most of the advantage in weight of normal lambs was made during the first six weeks of life. Wardrop (1968) also found that in a prime lamb producing flock under southern Australian conditions, the correlation coefficient between liveweight at eight and seventeen weeks of age was 0.91. It was concluded that: (a) lambs that were lightweight at the normal sale time could be identified with reasonable confidence at about six weeks of age, and that (b) preferential treatment in the form of a concentrate diet offered sometime between six weeks of age and normal slaughter time, may reduce or eliminate the number of lambs carried-over beyond the end of the growing season. This thesis presents the results of studies designed to test these hypotheses.
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ItemEffect of body condition at calving on milk yield of the dairy cow( 1978)The experiments reported in this thesis were done at the Dairy Research Institute (Ellinbank), Department of Agriculture, Victoria. This Institute is situated 100 kilometres east of Melbourne in the West Gippsland Region. The information currently available on the effect of precalving feeding on subsequent milk yield of grazing dairy cows is limited and largely of a qualitative nature. This thesis attempts to provide quantitative information on which feed management decisions can be made in the precalving period with some degree of confidence. The design, analysis and interpretation of the two experiments reported in this thesis were done primarily by myself. I was also actively involved in development of the condition scoring system reported in this thesis and in collecting, analyzing and interpreting data in order to provide an objective description of the condition scoring system. Chapter 1 reviews the literature on precalving feeding of the dairy cow indicating the apparent conflict in the results of different experiments which cannot be explained because of the confounded design and inadequate reporting of the results of experiments. Gaps in our current knowledge of precalvins feeding are also highlighted. Chapter 2 reports on an experiment which was done as part of a series of three experiments at Ellinbank to determine the relative importance of precalving liveweight change and body condition at calving on milk yield of dairy cows. These three experiments have been written up and accepted for publication in the Australian Journal of Experimental Agriculture and Animal Husbandry. Chapter 3 describes a system for scoring the body condition of dairy cows which was developed at Ellinhank with the assistance of the author. Chapter 4 reports on an experiment which quantifies the effect of body condition score at calving on milk yield under two levels of feeding after calving. This experiment and a more recently completed experiment with stall- fed cattle in different condition scores are to be combined and submitted shortly to the Australian Journal of Experimental Agriculture and Animal Husbandry. In Chapter 5 the experimental results are discussed in the light of continuing work and the industry significance of the work is emphasized.
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ItemStudies with annual Medicago species in the wheat belt( 1965)This thesis was prepared while the author was employed with the Victorian Department of Agriculture at the Mallee Research Station, Walpeup, and at the Longerenong Agricultural College, Dooen. It is in the form of five papers. The first is a review on the place of barrel medic (Medicago tribuloides Desr) in the Australian wheat belt. The review was published in J. Aust. Inst. Agric. Sci. (1965) 31: 25-35. This provides the background information for the experimental work which is prefaced by a section on climate and soils at Walpeup. The experimental work is concerned with a comparison of four annual medics in pure swards, competition between two annual medics, root studies, and the residual effect of superphosphate on medic pastures in the year after a wheat crop.
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ItemThe influence of nutritional factors in the development of postweaning diarrhoea in early weaned pigs( 1984)1. The study concerned the significance of change of diet and feeding method on the clinical, pathological and growth responses of 3- to 4-week-old pigs when subjected either to challenge with an enterotoxigenic serotype of Escherichia coli or exposed to 'natural' infection with E.coli. It involved experiments with both hysterotomy-derived specific pathogen-free (SPF) piglets and conventionally reared animals. The dietary treatments involved comparisons between (i) wet versus dry feeding and (ii) skim milk versus soyabean (SB) meal as the major dietary protein source. 2. Under closely controlled SPF conditions, thirty-five 28-day-old piglets were used in five experiments. In the first four experiments, two groups were changed from a liquid cow's milk diet to a milk-based diet (termed the 'basal' diet), given either in wet or dry form. Within each group, half of the animals were orally challenged with enterotoxigenic E.coli (ETEC) bearing the K88 antigen and the remainder, serving as controls, were challenged with a non-pathogenic K12 E.coli strain. ETEC-infected piglets fed the dry, basal diet developed severe diarrhoea, depression and dehydration and at necropsy exhibited severe lesions in the small intestine associated with extensive bacterial adherence and marked reduction in intestinal lactase activity. Infected piglets fed the basal diet as a gruel had only mild diarrhoea, accompanied by limited bacterial adherence and minor mucosal and physiological changes. Control piglets, fed either dry or wet, remained clinically healthy and the morphology of the intestinal mucosa was normal. In the fifth experiment, two groups were changed from the liquid cow's milk diet to either a dry-fed basal diet or a dry-fed SB-based diet; each group consisted of both infected and control animals. Control piglets on both diets remained clinically normal with only minor mucosal changes; but the intestinal lactase activity of those fed the SB diet was depressed. Infected piglets fed the SB diet developed mild diarrhoea, depression and dehydration. Infected piglets fed the basal diet had no diarrhoea but were depressed. Bacterial colonization, mucosal and physiological changes were relatively more severe in the SB-fed animals than in those fed the basal diet. 3. Under conventional conditions, a total 0f one hundred and seventy-six piglets, from the Mt Derrimut herd, were used in three experiments. In each of these experiments, pigs were allocated among four dietary treatments: dry, basal; wet, basal; dry, SB; and wet, SB. In Expt 1, a total of twenty-four pigs were orally inoculated with K88 ETEC following their transfer at weaning to non-specialized pen accommodation (at the Attwood Institute for Veterinary Research). In Expts 2 and 3, (conducted at the Mt Derrimut Pig Centre), ninety-six and fifty-six pigs respectively were moved at weaning into specialized weaner accommodation that was routinely used for early weaning on a batch basis. No inoculations with ETEC were performed in these two experiments. In Expt 1, all pigs remained clinically normal except for one pig fed the SB diet dry. Post-mortem studies conducted on four selected pigs from each treatment group revealed very limited colonization by ETEC but without marked changes in gut morphology (although K88 ETEC were present in faecal materials). In Expts 2 and 3, natural infection with ETEC and manifestation of PWD (postweaning diarrhoea) occurred. As compared with the SB diet, the basal diet particularly when fed wet, resulted in a less severe diarrhoea. Morphological and physiological changes in the small intestine were less pronounced and bacterial adherence was less extensive. Whether the SB diet was fed wet or dry made little difference in these respects. In the first 14 days post-weaning pigs fed the basal diet, especially when this was fed wet, made faster and more efficient weight gains than those given the SB diet. The degree of infection was more widespread and severe in Expt 3 than in Expt 2. In Expt 3, the superiority of the milk-based diet compared to the SB diet was relatively greater during the first 14 days post-weaning. 4. The results indicated that both the type of diet and the form in which the diet was fed, significantly influenced the extent of colonization of the gut by ETEC, the severity of PWD and growth performance. The effects of feeding method were more apparent in the SPF piglets than in the conventional piglets. This was attributed to the greater influence of uncontrolled variables in the latter situation. 5. The greater variability of performance under the conventional rearing conditions and the marked difference in response to ETEC in Expt 1 compared with that in Expts 2 and 3 suggest that in addition to the dietary factors examined, other factors, such as the immune status of the animal, the level of 'background' pathogenic challenge and the physical environment were implicated in the pathogenesis of PWD.