1,178 research outputs found
Ascites in chickens : oxygen consumption and requirement related to its occurrence
No full textThe present thesis describes the etiology of heart failure syndrome (HFS) and ascites in broiler chickens.In The Netherlands, ascites, as a cause of mortality in broiler chickens, is increasing steadily. Rates of mortality in broiler flocks in practice, related to HFS and ascites, during a growth period of approximately six weeks, nowadays vary between 2 and 10 percent. This depends on a genetically predisposition of the flock and on effects of environmental factors which can differ between different farms.The occurrence of ascites at high altitudes and its relation to the low oxygen pressure in the air is well documented (chapter 1). Hypoxia (a low oxygen tension in the inspired air) causes an increase in pulmonary arterial pressure in humans and in animals. The consensus of all studies on hypoxic pulmonary pressor response is that besides an increased heart rate, pulmonary vasoconstriction is an eminently important component in a control system that matches ventilation and perfusion and that preserves arterial P 02 . A reduction of the oxygen tension in the air stimulates a recruitment of reserve capillaries in the pulmonary vascular bed which previously were not perfused. Vasoconstriction of arterioles in the main pulmonary blood stream increases the local resistance to flow and causes a redistribution of blood towards reserve capillaries.The increased total resistance to flow by the use of more small tubes distributing the blood to all regions of the lungs (by vasoconstriction) increases distinctly the work-load of the right ventricle of the heart (chapter 1). Increased blood pressure in the lungs and failure of the right heart ventricle causing an increased blood pressure in the veins of the systemic circulation results in edema in different parts of the body (lung edema, hydropericard and ascites).Now the same symptoms of edema and right ventricle hypertrophy and failure, known from high altitudes, are found in modern broiler-chicken breeds in non hypobaric conditions at sea level.Experimental results obtained with different species of animals at high altitudes and at sea level showed that at both locations at least partly the same initial conditions are responsible for the development of HFS and ascites.Hypoxia in the sense of a low oxygen tension in the airways appears not to be directly responsible for the pulmonary pressure response. More important is the result of hypoxia which can be measured as low values for oxygen tension in the blood (hypoxemia) and which directly can affect pulmonary arterioles. Hypoxemia leads to tissue oxygen deprivation or anoxia which directly can influence oxidative phosphorylation and which can induce vasoconstriction of pulmonary arterioles.Experimental results obtained with hypoxic chickens at high altitudes and with normoxic fast growing chickens at sea level indicate that in both cases hypoxemia and anoxia can be the initiating factors leading to an inhibited oxidative phosphorylation inducing vasoconstriction of pulmonary arterioles. The subsequent increased pulmonary blood pressure results in hypertrophy and failure of the right heart ventricle and in edema including ascites. From this point of view a hypothesis was formulated that changes in metabolizable energy intake (MEi) and in energy partitioning in the body affecting oxidative phosphorylation quantitatively and thus oxygen requirements could be initial factors in the development of ascites. In accompaniment with changes in oxygen supply these factors could be responsible for pathophysiological processes in the body inducing HFS and ascites. Thyroid hormones initiating and stimulating oxidative phosphorylation therefore could interfere in those pathophysiological processes.Experiments with different populations of broiler chickens combined with effects of different environmental factors described in chapters 2, 3, 4, 5 and 6 were carried out. The aim was to explore the impact of changes in MEi, together with changes in energy partitioning into deposited protein and fat and into heat, and of changes in oxygen consumption on indices of susceptibility for ascites in chickens. Differences in MEi, in deposition of energy (RE) and in heat production (HP) between populations of chickens in experiments were obtained by using following experimental factors:1 . Different genetic groups of chickens obtained by differences in selection pressure on a fast growth rate and on a low feed conversion ratio (FCR) affecting MEi, energy partitioning, and energy efficiency for growth (RE/MEi).2. Different dietary compositions, differences in energy density affecting MEi and nutrient composition affecting deposition of energy (RE), deposition of protein (RIP), deposition of fat (RF), and heat production per body weight gain (HP/BWG).3. Different ambient temperatures affecting mainly MEi, HP/BWG, and oxygen consumption per deposition of protein (OXc/RP).4. Supplementation of exogenous thyroxine (T4) in diets affecting MEi, and directly OXc followed by responses of HP and RE.In the experiments was shown that populations which combined a low FCR with a fast growth rate exhibited low values for HP/BWG and OXc/RP and high values for RE/MEi and were more susceptible to ascites relative to other populations (chapters 2, 3, 4, 5, and 6). These results indicated that in fast growing stocks, showing low FCR values as a result of high RE/MEi values, a fast protein accretion was achieved together with a reduced ability to convert chemical energy to metabolic heat. A low rate of HIP and thus of OXc, which is not matched to high oxygen requirements, for synthesis and maintenance of protein in tissues, will lead to hypoxemia, heart failure and ascites.Fast growing birds with a low FCR showed less flexibility in metabolic adaptation to a changed environment such as a high fat content in diets and a low ambient temperature. Especially a low ambient temperature will demand a high rate of HP and OXc (chapter 2, 3, 4, and 6). An environment demanding a high level of OXc can induce an imbalance between oxygen supply and requirement in birds. A low FCR can be due to an inability to increase OXc above a certain level. This can reduce the transformation of dietary energy in heat energy.The same fast growing stocks exhibiting a low FCR, if exposed to a low temperature, showed distinctly lower oxygen tension values in venous blood relative to other stocks. The metabolic inability of birds to respond sufficiently to a low temperature by a higher rate of oxygen consumption, inducing hypoxemia and pulmonary hypertension, again can be responsible for the development of ascites. Experimental results described in chapters 3 and 4 support the hypothesis that hypothyroidism reducing HIP and OXc might be one of correlated responses to a selection for a low FCR.Results described in chapter 5 show that supplementation of exogenous thyroxine (T4) to chickens susceptible for ascites can have positive effects on initial conditions responsible for the development of ascites in birds. Supplementation of T4 resulted, only in a population which was susceptible for ascites, in lower haematocrits and haemoglobin contents in blood. High values of both blood parameters are indices of susceptibility for ascites. T4 added to diets also increased adaptive responses of birds, which were susceptible for ascites, to a low ambient temperature, with respect to oxygen consumption. The experimental results reveal that a low thyroid hormone activity might cause impaired adaptive responses of birds to an unfavourable environment which can induce ascites.From the results is concluded that selection procedures and environmental factors which result in decreased values for heat production per gram of body weight gain and in decreased values for oxygen consumption per gram of deposited protein (both of them are related to a decreased feed conversion ratio) will increase the susceptibility for ascites in populations of broiler chickens
Deriving Regression Lines Without Calculus
No full textThis article, C.W. Puritz of the Royal Grammar School - High Wycombe, describes a method to calculate the least squares line algebraically. First, the author uses a numeric example, which uses calculus, then describes a simpler algebraic method. This is a great lesson plan for those instructors attempting to teach this method with having students with prior knowledge of calculus. The author uses a step by step approach to help best describe both the technique and subsequent ways to best teach this method
Die ersten organisch-chemischen Synthesen
No full textThe first total synthesis of an organic compound, that of the hydrocyanide by C.W. Scheele in 1783 is remembered and it is pointed to its significant effect on further famous syntheses in the first half of the 19th century. A nearly unknown reaction done by J.W. Döbereiner in 1816 is considered as the precursor of today's technical important syntheses of hydrocarbons and other organic products starting from coal and water. Short biographies of Scheele and Döbereiner are included
Development and optimisation of a duplex real-time reverse transcription quantitative PCR assay targeting the VP7 and NS2 genes of African horse sickness virus
No full textNucleotide sequences of 52 South African isolates of African horse sickness virus (AHSV) collected during 2004–2005 and including viruses of all nine AHSV serotypes, were used to design and develop a duplex real-time reverse transcription quantitative PCR (RT-PCR) assay targeting the VP7 (S8) and NS2 (S9) genes of AHSV. The assay was optimized for detection of AHSV in fresh and frozen blood of naturally infected horses. Assay performance was enhanced using random hexamers rather than gene-specific primers for RT, and with denaturation of double-stranded RNA in the presence of random hexamers. The assay was efficient with a linear range of at least five orders of magnitude. The analytical sensitivity of the assay was 132 copies of the target genes (4125 copies per ml of blood), and the assay was at least 10-fold more sensitive than virus isolation on BHK-21 cells. The assay was also highly specific because it did not detect related orbiviruses, such as bluetongue and equine encephalosis viruses.ID: S0166093410000893; M3: Article; Accession Number: S0166093410000893; Author: M. Quan (a, b, ⁎); Author: C.W. Lourens (a, b); Author: N.J. MacLachlan (c); Author: I.A. Gardner (d); Author: A.J. Guthrie (a); Affiliation: Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort 0110, South Africa; Affiliation: Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort 0110, South Africa; Affiliation: Equine Viral Disease Laboratory, Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA; Affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA; Keyword: African horse sickness virus; Keyword: Real-time quantitative RT-PCR; Keyword: VP7 gene; Keyword: NS2 gene; Keyword: Duplex; Number of Pages: 8; Language: English
Nota, betreffende berekeningen omtrent rivierverbeteringen: opgemaakt door den ingenieur van den Rijkswaterstaat C.W. Lely
No full textHydraulische basis voor de normalisatiewerken van de grote rivieren. Berekingen van optimale breedte en diepte
Onderzoek naar signaalgeneratie met behulp van fasedraaiers ten behoeve van reflectie-compensatie in een F.M.-C.W. radarsysteem
No full textVoor onderzoek aan de troposfeer wordt gebruik gemaakt van een F.M.-C.W. radarsysteem. Een aspect van het radarsysteem waarnaar nog onderzoek gewenst is, is de onderdrukking van de overspraak van zender naar ontvanger, en van sterke reflecties aan nabije obstakels: deze signalen houden nl. het gevaar in van oversturing van de ontvanger. Dit aspect is met name van belang voor een mogelijk nog te realiseren F.M. -C.V. radarsysteem met één antenne…Applied SciencesElectrotechniekTelecommunicatie- en Verkeersbegeleidingssysteme
A Fourier-Based Valuation Method for Bermudan and Barrier Options under Heston’s Model
No full textWe develop an efficient Fourier-based numerical method for pricing Bermudan and discretely monitored barrier options under the Heston stochastic volatility model. The two-dimensional pricing problem is dealt with by a combination of a Fourier cosine series expansion, as in [F. Fang and C.W. Oosterlee, SIAM J. Sci. Comput., 31 (2008), pp. 826–848, F. Fang and C. W. Oosterlee, Numer. Math., 114 (2009), pp. 27–62], and high-order quadrature rules in the other dimension. Error analysis and experiments confirm a fast error convergence.Delft Institute of Applied MathematicsElectrical Engineering, Mathematics and Computer Scienc
Nota betreffende het verband tusschen bodemhelling en kromtestraal bij rivieren, opgemaakt door den ingenieur van den Rijkswaterstaat dr. C.W. Lely
No full textRelatie kromtestraal en dwarshelling van rivieren, bevat data van de Nederlandse rivieren
Lage prijs nodigt uit tot groter gebruik : niet elke tarwe is geschikt als voedergrondstof
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