School of Agriculture, Food and Ecosystem Sciences - Theses
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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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ItemA study of factors influencing in vitro stability of nitrate reductase from wheat leaves( 1979)This review and the following chapters are concerned predominantly with the processes occurring in higher and lower plants which regulate the amount of NR present in vitro as controlled by degradation, and the level of activity of the existing enzyme. Those factors regulating the synthesis of NR will not be discussed in any detail but only mentioned where they also affect other mechanisms regulating NR. Nitrate reductase is unstable both in vivo and in vitro (101,193, 252). In vitro instability occurs since the isolation of enzymes and other cell components from plant tissue involves disruption of the plant cell. This results in mixing of substances which in situ were rigidly compartmentalized and is likely to result in the isolation of an enzyme which is modified from its native form. Factors present in plant cells which make plant proteins particularly unstable in vitro have been reviewed by Stahrran (216) and Pirie (157). They include vacuole acids, carbohydrates, hydrolytic and oxidative enzymes and phenolic components and their derivatives. In vivo variation in activity occurs in response to a number of other factors, including tissue age (103,129,166,243,264) and environment (15,72,82,1.03,129,261). Tissue age has been shown to influence the activity or stability of NR extracted from a number of species including corn (194,195,264), wheat (221), oats (194,195), tobacco (195) and barley (48). Nitrate reductase has been demonstrated in nearly all plant parts (16) and its ubiquitous presence suggested in higher plants (16,184). Nevertheless, due to the number of factors involved, detection of activity would only occur given suitable physiological and environmental conditions together with use of the correct extraction and assay procedure. Determining if the level of activity derived is an accurate estimate of the in situ activity is even more difficult. This has been attempted by correlating NR activity and grain or plant nitrogen (28, 36) . In vivo instability is indicated by the decline in NR activity with the onset of darkness, depletion of nitrate supply, and water or heat stress (11,82,121,168,235). Under appropriate conditions these factors could also affect the enzyme in vitro.
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