Veterinary Science - Theses
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ItemStudies on the helminth parasites of Australasian mammals( 1989)The papers presented in this thesis constitute a study of the systematic and ecology of some of the helminth parasites of Australasian mammals. Systematics is here understood in its broadest sense. It begins with the description of new species and the redescription of previously described taxa, but proceeds from this basis to a consideration of the systematic status of species or species groups, including their phylogeny, based not only upon the morphological data supplied through the initial taxonomic studies, but also from a study of the life histories of the organisms involved, their ecology and geographic distribution, and finally the effects on their hosts. Examples are provided within the body of the thesis of how this approach, using data from different sources, is applied in elucidating the systematic of a variety of helminth parasites. The particular approach taken with individual species depends upon the current state of knowledge of their biology and the avenues of investigation most likely to lead to significant results. (From Introduction)
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ItemThe effects of manipulating reproduction on the productivity and profitability of dairy herds with graze pasture( 1989)Two computer simulation models were developed to predict the effects of manipulating dairy cow reproduction on the productivity and profitability of dairy herds which graze pasture. The first computer model predicted calving patterns of herds, and after testing its predictions, was used to assess the relative importance of different factors affecting reproduction of cows. The effects of initial calving pattern, oestrus detection efficiency, calving to first oestrus interval distribution, conception rate, and drugs which modify the oestrous cycle of cows were predicted and their influence on the profitability of achieving a six week calving pattern estimated. The model indicated that the calving pattern of a herd and the achievement and maintenance of efficient oestrus detection were probably the two most important factors affecting profitability. Increasing conception rate through the use of new technologies provided the greatest potential for increasing the profitability of achieving such a pattern. The second computer model, which was called “UDDER”, predicted the milk production of herds with different calving patterns. Because many factors interact to determine milk production, UDDER was developed to account for variables such as pasture growth, stocking rate, supplementary feeding, grazing management, and fodder conservation. To predict milk production, models were developed to stimulate the utilisation of energy within the dairy cow, estimate the intake of cows pasture, and predict the accumulation and quality of pasture on farms at different times of the year. Experimental data were analysed to derive some relationship for these models, and others were obtained directly from the literature. An experiment was conducted on three commercial dairy farms to collect data which could be used to test the accuracy of UDDER. The results indicated that the program was capable of predicting the butterfat production of dairy herds to within 5% of actual measurements. UDDER was then used to evaluate different management options on these farms. The investigation highlighted that the result of a single chance in management depends on all other variables which interact within the farm system. For example, the change in farm income which occurs when calving pattern is modified depends on stocking rate, pattern of pasture production, drying off strategy, level of supplementary feeding, and milk pricing system. Because of the complex interactions which may occur, it is unwise to make general statements about farm management. Accurate advice can probably only be given at the individual farm level where the interactions can be accounted for and this would be very difficult without a computer model of some sort. Both computer simulation models have the potential to be used in the field to improve the accuracy of advice provided to farmers. They could also play a key role in directing research within the dairy industry. The models are a description of current understanding on how the pasture-based dairy production system operates, and provide a means of putting current knowledge to the test. They can be used to make predictions about the system, and if inadequacies in the models can be demonstrated and isolated, then weakness in current knowledge and understanding are highlighted. The models have already indicated that further research is necessary to refine our understanding of how grazing affects the accumulation of herbage, the influence of stage of lactation on herbage intake and herbage substitution during supplementary feeding, and substitution rates resulting when different supplements are fed. Since modelling is one of the only ways that the knowledge of a complex system can be incorporated in a form which can be used to make predictions, it will become an integral part of dairy research and the improved extension of research findings to the industry, but there is still much to be learnt about how these models should and could be used.