School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemPasture utilization for wool growth of weaner sheep in south western Victoria( 1988)Two series of experiments are described in this thesis. The first set of experiments report on the use of young, oesophageally fistulated sheep to collect herbage samples in grazing experiments. Secondly, the biological responses of Merino and Comeback weaner sheep to changes in pasture type and season of birth are described. The experiments were conducted at the Pastoral Research Institute, Hamilton, Victoria during 1982-86, where the author is employed as a Science Officer by the Victorian Department of Agriculture and Rural Affairs. Chapters 4 and 5 report the effects of several variables on the chemical composition of oesophageal fistula samples and have been submitted for publication (see below). Mr. P.C. Flinn and Professor A.R. Egan have been included as co-authors of Chapter 4 due to their contribution to chemical analysis of samples, and to planning of the experiment respectively. Mr. P.C. Flinn and Mr. J.F. Heard have been included as co-authors due to their assistance during the experiment described in Chapter 5. Differences between the growth, composition and nutritive value of lucerne/subterranean clover and perennial ryegrass/subterranean clover pastures are reported in Chapter 6. (More detailed data on the growth and composition of the pastures is available on request to the author). The effects of these pastures on the productivity of autumn and spring born, Merino and Comeback weaner sheep are presented in Chapters 7 and 8. It. is intended to submit these three chapters for publication. Mr. R.L. Thompson and Dr. J.M. Obst will be. included as co-authors when the results reported in Chapter 7 are published. The experiments reported in this thesis make up part of a larger project (Sheep Production Systems) for which Mr. Thompson and Dr. Obst are responsible. However I accept full responsibility for the collection of all data, analysis of results and preparation of the manuscripts. In addition, I was responsible for the design of experiments reported in Chapters 4, 5, 6 and 8. Details of publications are as follows:- Chapter 4 : Saul, G.R., Flinn, P.C. and Egan, A.R. (1988). The effect of fasting, breed and sample size on the chemical composition of pasture samples from fistulated weaned lambs (submitted to Australian Journal of Experimental Agriculture). Chapter 5 : Saul, G.R., Flinn, P.C. and Heard, J.F. (1986). The nutritive value of roughages before and after mastication by oesophageally fistulated sheep. Proceedings Australian Society of Animal Production 16, 351-54.
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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.