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Genetically select lines of Merino sheep have been bred at Trangie (NSW Agriculture and Fisheries) for resistance (R) or susceptibility (S) to fleece-rot and flystrike. It is believed that fleece characters are primarily responsible for the R or S phenotype. When transferred to the wetter coastal environment of Sydney, R and S sheep with no more than 6 weeks wool cover, continued to show significant differences in the incidence and severity of fleece-rot dermatitis. To test the hypothesis that these sheep might also exhibit differences in their local skin reactions and immune responsiveness, 3 intradermal injections of killed Pseudomonas aeruginosa were administered at monthly intervals. After primary intradermal challenge, R sheep had a higher incidence of skin induration and a stronger inflammatory response (increased induration diameter) than S sheep. Compared to S sheep, R sheep also developed higher levels of circulating antibodies against whole cell antigen and both inner and outer membrane proteins of P. aeruginosa. These responses were maintained in R sheep with each consecutive challenge while S sheep showed a decline in their immune responsiveness. Differences in antibody response against outer membrane proteins were also detected when antigenically naive sheep from each genetic line were sensitised by epicutaneous challenge with P. aeruginosa under experimental wetting conditions. Intradermal challenge of these animals 6 months later with outer membrane proteins, revealed a late maximum (72 h) in the development of induration diameters for R sheep while S animals showed maximal induration diameters by 24 h. However, there was no significant difference in induration response between 24 h and 72 h within each group of sheep.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
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The potential of cloning depends in part on whether the procedure can reverse cellular aging and restore somatic cells to a phenotypically youthful state. Here, we report the birth of six healthy cloned calves derived from populations of senescent donor somatic cells. Nuclear transfer extended the replicative life-span of senescent cells (zero to four population doublings remaining) to greater than 90 population doublings. Early population doubling level complementary DNA-1 (EPC-1, an age-dependent gene) expression in cells from the cloned animals was 3.5- to 5-fold higher than that in cells from age-matched (5 to 10 months old) controls. Southern blot and flow cytometric analyses indicated that the telomeres were also extended beyond those of newborn (<2 weeks old) and age-matched control animals. The ability to regenerate animals and cells may have important implications for medicine and the study of mammalian aging.  相似文献   
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Magneto-optical imaging was used to visualize the inhomogeneous penetration of magnetic flux into polycrystalline TlBa2Ca2Cu3Ox films with high critical current densities, to reconstruct the local two-dimensional supercurrent flow patterns and to correlate inhomogeneities in this flow with the local crystallographic misorientation. The films have almost perfect c-axis alignment and considerable local a- and b-axis texture because the grains tend to form colonies with only slightly misaligned a and b axes. Current flows freely over these low-angle grain boundaries but is strongly reduced at intermittent colony boundaries of high misorientation. The local (<10-micrometer scale) critical current density Jc varies widely, being up to 10 times as great as the transport Jc (scale of approximately 1 millimeter), which itself varies by a factor of about 5 in different sections of the film. The combined experiments show that the magnitude of the transport Jc is largely determined by a few high-angle boundaries.  相似文献   
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Sudden blindness associated with protothecosis in a dog   总被引:1,自引:0,他引:1  
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A survey of veterinarians' use of antibacterial drugs was conducted by distributing a questionnaire to Australian practitioners. Respondents were asked to indicate their general patterns of use of various systemic antibacterial drugs and drug combinations in dogs and their approach to certain specified clinical disorders. Overall, antibacterials of the p-lactam type (penicillins and cephalosporins) were most commonly used. Other antibacterials with substantial use were doxycycline, sulphonamide-trimethoprim, metronidazole, fluoroquinolones and clindamycin. Drug selection for different disorders was generally appropriate when compared with recommendations in recent texts, although inappropriate use was evident in some circumstances.  相似文献   
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