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Although often seen as a scale-independent measure, we show that the fractal dimension of the forest cover of the Cazaville Region changes with spatial scale. Sources of variability in the estimation of fractal dimensions are multiple. First, the measured phenomenon does not always show the properties of a pure fractal for all scales, but rather exhibits local self-similarity within certain scale ranges. Moreover, some sampling components such as area of sampling unit, the use of a transect in the estimation of the variability of a plane, the location, and the orientation of a transect all affect, to different degrees, the estimation of the fractal dimension. This paper assesses the relative importance of these components in the estimation of the fractal dimension of the spatial distribution of woodlots in a fragmented landscape. Results show that different sources of variability should be considered when comparing fractal dimensions from different studies or regions. 相似文献
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A 2-year-old Standardbred gelding was referred for a mass on the palmaromedial right front pastern which was accompanied by progressively worsening lameness. The mass was firm to palpation and covered by normal skin. Ultrasonographically, a smooth encapsulated mass was present, medial to the flexor tendons and palmar to the neurovascular bundle. Because of a poor prognosis for future athletic performance without surgical or chemotherapeutic intervention and economic constraints preventing further diagnostics and treatment, the horse was euthanised. Post-mortem magnetic resonance imaging, histopathology and immunohistochemistry revealed the mass to be a perivascular wall tumour, the first record of such a neoplasia in the horse. 相似文献
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Antoine Leduc Sylvain Souchet Marine Gel Fabienne Le Provost Marion Boutinaud 《Journal of animal science》2021,99(7)
In the dairy cow, negative energy balance affects milk yield and composition as well as animal health. Studying the effects of negative energy balance on dairy cow milk production is thus essential. Feed restriction (FR) experiments attempting to reproduce negative energy balance by reducing the quantity or quality of the diet were conducted in order to better describe the animal physiology changes. The study of FR is also of interest since with climate change issues, cows may be increasingly faced with periods of drought leading to a shortage of forages. The aim of this article is to review the effects of FR during lactation in dairy cows to obtain a better understanding of metabolism changes and how it affects mammary gland activity and milk production and composition. A total of 41 papers studying FR in lactating cows were used to investigate physiological changes induced by these protocols. FR protocols affect the entire animal metabolism as indicated by changes in blood metabolites such as a decrease in glucose concentration and an increase in non-esterified fatty acid or β-hydroxybutyrate concentrations; hormonal regulations such as a decrease in insulin and insulin-like growth factor I or an increase in growth hormone concentrations. These variations indicated a mobilization of body reserve in most studies. FR also affects mammary gland activity through changes in gene expression and could affect mammary cell turnover through cell apoptosis, cell proliferation, and exfoliation of mammary epithelial cells into milk. Because of modifications of the mammary gland and general metabolism, FR decreases milk production and can affect milk composition with decreased lactose and protein concentrations and increased fat concentration. These effects, however, can vary widely depending on the type of restriction, its duration and intensity, or the stage of lactation in which it takes place. Finally, to avoid yield loss and metabolic disorders, it is important to identify reliable biomarkers to monitor energy balance. 相似文献
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Impact of Endocrine‐Disrupting Chemicals on Reproductive Function in Zebrafish (Danio rerio)
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The prevalence of endocrine‐disrupting chemicals (EDCs) in the aquatic environment has been associated with the wide detection of alterations in the development and physiology of vertebrates. Zebrafish, as a model species, has been extensively used in toxicological research. In this review, we focus on recent published evidence of the harmful effects of EDCs on reproductive function in zebrafish, including skewed sex ratio, immature gonads, diminished sexual behaviour, decreased sperm count, reduced spawning and fertilization. These impairments mostly result from disruption to sex‐steroid hormones induced by endocrine disruptors. We also discuss other effects of exposure to EDCs. In EDC exposure research, despite incomplete assessments of altered gonad histopathology and sexual behaviour, these present potential effective biomarkers or pathways for evaluating the reproductive function in zebrafish on EDC exposure. To date, the pernicious effects of some EDCs on the reproductive performance in laboratory zebrafish are well understood; however, similar alterations remain for further determination in wild‐type fish and more kinds of EDCs. More studies should be performed under established scientific regulatory criteria to investigate the impact of EDCs on reproduction in zebrafish. Moreover, further research is required to explain the definite mechanism of sexual differentiation, which helps in understanding the shift of sexual phenotype with EDC exposure. 相似文献
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An investigation of sheep flocks in the main sheep raising areas of New South Wales showed that the itchmite Psorergates ovis was frequently associated with fleece derangement. In 26 of the 41 flocks examined, P. ovis was the only ectoparasite detected. P. ovis and the sheep body louse Damalinia ovis, were found in 5 flocks. No external parasites were found on sheep examined from the 10 remaining flocks. The type of fleece derangement most frequently recorded was rubbing which in some cases was combined with areas of chewed fleece. Among flocks, there were positive relations between the prevalence of fleece derangement and prevalence of itchmite or scurf and between itchmite count and mean scurf score. Within flocks, itchmite infested sheep or sheep with scurf had higher prevalences of fleece derangement than sheep on which no mites or no scurf were found. Itchmite infested sheep had a higher prevalence of scurf than those with no detectable mite infestation. There were no significant differences in itchmite populations or fleece derangement between untreated flocks and flocks treated with synthetic pyrethroids, organophosphates or arsenic and rotenone. 相似文献
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Chlamydiosis in workers at a duck farm and processing plant 总被引:4,自引:0,他引:4
DG HINTON A. SHIPLEY† JW GALVIN‡ JT HARKIN‡ RA BRUNTON† 《Australian veterinary journal》1993,70(5):174-176
SUMMARY An outbreak of chlamydiosis was Investigated in workers at a duck farm and processing plant during winter 1989. Chlamydia psittaci was isolated from ducks, but there was little evidence of clinical chlamydiosis in the ducks. Serological tests showed that 76% of workers had been exposed to Infection, 12% recently, 16% had not been exposed and 8% had inconclusive test results. There was a strong association (P < 0.05) between years of employment and exposure to Infection. Infection appeared to be contracted during the first year of employment. Measures were Implemented to reduce shed contamination and control rodents and wild birds. At the same time, ducks were medicated, the processing plant was modified, work practices were altered and workers were advised about chlamydiosis to reduce the risk of human infection. 相似文献
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Films of silicon dioxide (SiO2) were deposited at room temperature by means of catalyzed binary reaction sequence chemistry. The binary reaction SiCl4 + 2H2O --> SiO2 + 4HCl was separated into SiCl4 and H2O half-reactions, and the half-reactions were then performed in an ABAB ellipsis sequence and catalyzed with pyridine. The pyridine catalyst lowered the deposition temperature from >600 to 300 kelvin and reduced the reactant flux required for complete reactions from approximately 10(9) to approximately 10(4) Langmuirs. Growth rates of approximately 2.1 angstroms per AB reaction cycle were obtained at room temperature for reactant pressures of 15 millitorr and 60-second exposure times with 200 millitorr of pyridine. This catalytic technique may be general and should facilitate the chemical vapor deposition of other oxide and nitride materials. 相似文献