A mouse model system was used to study various aspects of host and parasite relationships in Trypanosoma vivax infections. These included the phenomenon of antigenic variation, the variable parasite antigens responsible for this phenomenon, parasite-host adaption, host immune responses and the role of genes in the major histocompatibility complex in the control of infection. While the mouse model system has allowed investigation of these aspects of host parasite relationships, it is clear that the system is much more limited than those generally used in T. brucei spp and T. congolense infections. This is indicated by the discovery that not all VATs of T. vivax were equally infective for mice, though in some cases infectivity could be improved by bovine serum supplementation and/or immunosuppression of the mouse host. In the case of rats, infection was even restricted to a smaller number of the VATs studied. It was, however, possible to biochemically characterize the variable surface antigen carried by T. vivax and show its similarity to those carried by T. brucei and T. congolense. The H-2 complex was found not to influence acquired resistance of inbred strains. Cyclic transmissions of T. vivax infections to goats combined with chemotherapy were carried out in an attempt to induce protection to subsequent infection as has been shown in T. brucei and T. congolense infections. Such protection could, however, not be obtained, The failure of the metacyclic VATs to induce immunity, was perhaps due to rapid decrease in antibody titres to bloodstream VATs found after treatment and prior to rechallenge. The usefulness of the mouse model system in elucidating the mechanisms responsible for the non-H-2 linked differences in susceptibility to T. vivax infections should be further explored and its relevance to mechanisms of trypanotolerance in domestic ruminants defined. 相似文献
Following concomitant intravenous administration of Tomanol and sodium penicillin G to six Dutch Friesian dairy cows a significant decrease in total body clearance of penicillin (34.7%) and a prolongation of the elimination half-life of penicillin (17.2%) was observed. Tomanol did not affect other pharmacokinetic parameters such as rate constants of drug transfer (k12/k21, alpha en beta), distribution volume of the central compartment (V1), and extrapolated serum drug levels. Intravenous or intramuscular administration of Tomanol had no effect on the tissue distribution of penicillin G, because neither a change in the ratios of muscle to serum and of kidney cortex to serum nor a change in an induced steady state level of low penicilline G serum concentrations was observed. From the data obtained it is concluded that concomitant Tomanol administration with penicillin induces an elevation of the serum penicillin concentration and prolongs the persistence of penicillin residues in carcass meat and organs. 相似文献
1. Two experiments were conducted to test the hypothesis that, as dietary protein concentration is increased, increments of response gradually diminish as egg output approaches an asymptotic value; and that the resulting response curve is consistent with a model (the “Reading model”) which assumes that the shape of the curve is a function of individual variation in body weight and potential egg output.
2. Each experiment involved a total of 3 888 laying pullets. Nine diets, with crude protein contents ranging from 87 to 212 g/kg, were used in the first experiment and ten diets, with protein contents ranging from 81 to 215 g/kg, in the second experiment. Diets were denned in terms of their calculated contents of essential amino acids and the same, well‐balanced amino acid profile was used at all protein contents within one experiment. Supplementary experiments were conducted to identify the limiting amino acid (s) in the experimental diets.
3. Treatments were applied for ten weeks, starting at 30 or 32 weeks of age. Average egg output on the highest protein diets was 57.0 g/bird d in the first experiment, which used White Leghorn pullets, and 53.7 g/bird d in the second experiment, which used a crossbred brown‐egg stock.
4. The response curves obtained showed diminishing returns and, in the second experiment, a clear plateau was reached. The Reading model was fitted and compared with a two‐straight‐line model and with curves derived from quadratic and inverse polynomial equations. Only the Reading model proved satisfactory for the interpretation of the data, as judged by goodness of fit and estimation of the optimum amino acid input. Although alternative models may provide a good fit when dealing with a single set of data, none of the alternatives is consistently satisfactory when considering the results of more than one experiment. 相似文献
1. Four experiments were conducted on broiler chickens between one and three weeks of age to determine their response to dietary protein concentrations.
2. Diets prepared by serial dilution of a concentrated protein mixture, well‐balanced with respect to all essential amino acids, were fed in three experiments, while in a fourth experiment, a lysine‐deficient protein mixture was used.
3. Response curves relating body‐weight gain to increasing concentrations of protein and of lysine intake are presented.
4. A table is presented from which optimum protein intakes can be calculated according to changes in input and output costs and changes in growth potential of the chickens. 相似文献
Thirty isolates of Haemophilus pleuropneumoniae from clinical and slautherhouse cases of porcine Haemophilus pleuropneumonia in Saskatchewan as well as six isolates from British Columbia and Ontario were subjected to cultural, biochemical, serological and antibiotic sensitivity tests. All strains were Gram-negative pleomorphic rods or coccobacilli which grew only in the presence of V factor and all produced porphyrin from delta-aminolaevulinic acid. Biochemically, the organism was positive for urease, O-nitrophenyl-β-D-galactopyranosidase and the fermentation of sucrose, mannitol, dextrose, lactose and xylose, but was usually negative for indole. Most strains of H. pleuropneumoniae were sensitive to chloramphenicol, furamazone, carbenicillin and ampicillin, but only about 50% were sensitive to tetracycline. Serotype 5 was more common than serotype 1 or the untyped strains among Saskatchewan isolates. In addition, serotype 3 was identified from British Columbia.
Retrospective epidemiological studies showed that Haemophilus pleuropneumonia occurred and recurred on farms in the Saskatoon and adjoining districts, serviced by the diagnostic laboratories of the Western College of Veterinary Medicine and that the disease was more common among three month old pigs during the fall-winter season.
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