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F Ardón A Döhring X Le Thi KF Weitze D Waberski 《Reproduction in domestic animals》2003,38(2):161-165
The goal of this study was to determine the ability of the Hanover gilt model to assess in vivo fertilizing capacity of preserved sperm and to consider whether any modifications to this model were needed. This model evaluates the fertilizing capacity of semen based on the fertilization rate, the rate of normal embryos and the accessory sperm count of 3–5‐day embryos. Its distinguishing characteristics are the use of one‐time insemination of sperm in reduced numbers, of spontaneously ovulating gilts and of ovulation detection through ultrasound examination of ovaries. Reduced sperm numbers allow for an accurate evaluation of the fertilizing potential of different semen treatments, thereby avoiding the compensatory effect of doses calibrated to maximize fertility. The model's usefulness was assessed in a trial run designed to compare the fertilizing capacity of liquid boar semen diluted into two different extenders. The diluent, the boar and the backflow, had no significant effect on any of the parameters studied. Gilts inseminated less than 24 h before ovulation had a significantly higher (p < 0.01) fertilization rate and accessory sperm cell count (p < 0.05) than those inseminated more than 24 h before ovulation. Very good/good embryos from homogeneous litters (only very good/good embryos were present) had a significantly higher (p < 0.01) accessory sperm count than those from heterogeneous litters (at least one embryo was of a different quality and/or oocytes were present). Both very good/good and degenerated/retarded embryos from heterogeneous litters had low accessory sperm numbers. This suggests that accessory sperm count is significantly related to the quality of the litter, but not to the quality of the embryo within gilts. It can be concluded that the Hanover gilt model is sensitive enough to show fertility differences (in this study, those associated with in vivo ageing of semen), while using relatively few gilts and little time. 相似文献
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Buma B. Harvey B. J. Gavin D. G. Kelly R. Loboda T. McNeil B. E. Marlon J. R. Meddens A. J. H. Morris J. L. Raffa K. F. Shuman B. Smithwick E. A. H. McLauchlan K. K. 《Landscape Ecology》2019,34(1):17-33
Context
Predicting ecosystem resilience is a challenge, especially as climate change alters disturbance regimes and conditions for recovery. Recent research has highlighted the importance of spatially-explicit disturbance and resilience processes to long-term ecosystem dynamics. “Neoecological” approaches characterize resilience mechanisms at relatively fine spatio-temporal resolutions, but results are difficult to extrapolate across broad temporal scales or climatic ranges. Paleoecological methodologies can consider the effects of climates that differ from today. However, they are often limited to coarse-grained spatio-temporal resolutions.
MethodsIn this synthesis, we describe implicit and explicit examples of studies that incorporate both neo- and paleoecological approaches. We propose ways to build on the strengths of both approaches in an explicit and proactive fashion.
ResultsLinking the two approaches is a powerful way to surpass their respective limitations. Aligning spatial scales is critical: Paleoecological sampling design should incorporate knowledge of the spatial characteristics of the disturbance process, and neoecological studies benefit from a longer-term context to their conclusions. In some cases, modeling can incorporate non-spatial data from paleoecological records or emerging spatial paleo-data networks with mechanistic disturbance/recovery processes that operate at fine spatiotemporal scales.
ConclusionsLinking these two complementary approaches is a powerful way to build a complete understanding of ecosystem disturbance and resilience.
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The comparative pathogenicity of four serovars of Actinobacillus (Haemophilus) pleuropneumoniae 总被引：1，自引：0，他引：1
The pathogenicity of 2 isolates of each of serovars 7, 3, 1 and 2 of Actinobacillus pleuropneumoniae was tested by intranasal inoculation into 60, 6-week-old large white pigs. Four dose rates varying from 0.27 to 560 x 10(6) organisms per pig with 10-fold serial dilutions were used. Surviving pigs were necropsied 7 days after inoculation. The proportion of pigs dying and developing gross lesions following infection was significantly greater for pigs given serotype 1 than for each of the other 3 serotypes, which did not differ significantly from each other. Twelve of 16 pigs given either of the 2 isolates of serovar 1 died after acute illness and 1 of 44 pigs given either of the 2 isolates each of serovars 7, 3 and 2 died. Pigs given serovar 1 showed high temperatures, severe respiratory distress, frothy haemorrhagic nasal discharge and weight loss. Lung lesions were produced in all 16 pigs given serovar 1, in 7 of 14 pigs given serovar 7, 7 of 14 pigs receiving serovar 3 and in 5 of 16 pigs given serovar 2. The lethal infections were characterised by a severe acute fibrinohaemorrhagic necrotising pleuropneumonia, whereas non-lethal cases had lung lesions ranging from necrotising purulent pleuropneumonia to abscessation. Significant differences between isolates in proportions of tissues culture positive for A. pleuropneumoniae for serovars 7 and 2, but not for serovars 3 and 1 suggested that isolates may vary in virulence within serovars, but more detailed studies are needed to clarify this point. 相似文献
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The agricultural use of synthetic insecticides usually protects crops but imposes strong selection pressures that can result in the development of resistance. The most important resistance mechanisms are enhancement of the capacity to metabolically detoxify insecticides and alterations in target sites that prevent insecticides from binding to them. Insect control methods must incorporate strategies to minimize resistance development and preserve the utility of the insecticides. The most promising approach, integrated pest management, includes the use of chemical insecticides in combination with improved cultural and biologically based techniques. 相似文献
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Brian H. Aukema Jun Zhu Jesper Møller Jakob G. Rasmussen Kenneth F. Raffa 《Forest Ecology and Management》2010
Bark beetles are largely known for their ability to undergo intermittent population eruptions that transform entire landscapes and pose significant economic hardships. However, most species do not undergo outbreaks, and eruptive species usually exert only minor disturbances. Understanding the dynamics of tree-killing noneruptive species can provide insights into how beetles persist at low densities, and how some spatiotemporal patterns of host predisposition may more likely favor breaching eruptive thresholds than others. Elucidating mechanisms behind low-density populations is challenging, however, due to the requirement of long-term monitoring and high degrees of spatial and temporal covariance. We censused more than 2700 trees annually over 7 years, and at the end of 17 years, in a mature red pine plantation. Trees were measured for the presence of bark beetles and wood borers that breed within the primary stem, root weevils that breed in root collars, and bark beetles that breed in basal stems. We quantify the sequence of events that drive this decline syndrome, with the primary emergent pattern being an interaction between below- and above-ground herbivores and their fungal symbionts. This interaction results in an expanding forest gap, with subsequent colonization by early-successional vegetation. Spatial position strongly affects the likelihood of tree mortality. A red pine is initially very likely to avoid attack by tree-killing Ips beetles, but attack becomes increasingly likely as the belowground complex spreads to neighboring trees and eventually make trees susceptible. This system is largely internally driven, as there are strong gap edge, but not stand-edge, effects. Additional stressors, such as drought, can provide an intermittent source of susceptible trees to Ips beetles, and elevated temperature slightly accentuates this effect. New gaps can arise from such trees as they subsequently become epicenters for the full complex of organisms associated with this decline, but this is not common. As Ips populations rise, there is some element of positive feedback, in that the proportion of killed trees that were not first colonized by root organisms increases. This positive feedback is very weak, however, and we propose the slope between beetle population density and reliance on host stress as a quantitative distinction along a gradient from noneruptive through eruptive species. Almost all trees colonized by Ips were subsequently colonized by wood borers, likely a source of negative feedback. We discuss implications to our overall understanding of cross-scale interactions, between-guild interactions, forest declines, and eruptive thresholds. 相似文献
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Objective To investigate the effects of two doses (200 and 400 mg) of a water-soluble gonadotrophin-releasing hormone vaccine on the ovarian activity of 2-year-old fillies.
Design A controlled vaccination dose rate experiment.
Animals Six 2-year-old Australian Stock Horse fillies were randomly allocated to three treatment groups: unvaccinated controls, those receiving 200 mg of the vaccine and those receiving 400 mg of the vaccine.
Results Ovarian activity of the treated fillies was suppressed at the peak of the breeding season while that of the untreated controls continued normally. The control fillies displayed oestrous activity and behaviour. Suppression of ovarian activity occurred for 25 and 30 weeks in the 200 and 400 mg groups, respectively. These differences were not significant. Ovarian activity ceased 2 to 3 weeks after primary vaccination. Antibody titres were low (330) until after the booster immunisation when they rapidly peaked at 22,000 and 28,000 in the 200 mg and 400 mg groups, respectively. Plasma progesterone concentrations of the treated fillies remained below 3.18 nmol/L while GnRH was suppressed. The vaccine had no significant effect on plasma androstenedione concentrations. Recovery from the effect of the vaccine was associated with development of ovarian follicles, normal oestrous behaviour and ovulation. Three of the four treated fillies and one of the controls conceived during the next breeding season and foaled normally. All the treated fillies conceived and produced normal foals in the following two breeding seasons.
Conclusion Both dose rates suppressed ovarian function and prevented oestrous behaviour. These effects were reversible and the subsequent fertility of the vaccinated fillies was normal. 相似文献
Design A controlled vaccination dose rate experiment.
Animals Six 2-year-old Australian Stock Horse fillies were randomly allocated to three treatment groups: unvaccinated controls, those receiving 200 mg of the vaccine and those receiving 400 mg of the vaccine.
Results Ovarian activity of the treated fillies was suppressed at the peak of the breeding season while that of the untreated controls continued normally. The control fillies displayed oestrous activity and behaviour. Suppression of ovarian activity occurred for 25 and 30 weeks in the 200 and 400 mg groups, respectively. These differences were not significant. Ovarian activity ceased 2 to 3 weeks after primary vaccination. Antibody titres were low (330) until after the booster immunisation when they rapidly peaked at 22,000 and 28,000 in the 200 mg and 400 mg groups, respectively. Plasma progesterone concentrations of the treated fillies remained below 3.18 nmol/L while GnRH was suppressed. The vaccine had no significant effect on plasma androstenedione concentrations. Recovery from the effect of the vaccine was associated with development of ovarian follicles, normal oestrous behaviour and ovulation. Three of the four treated fillies and one of the controls conceived during the next breeding season and foaled normally. All the treated fillies conceived and produced normal foals in the following two breeding seasons.
Conclusion Both dose rates suppressed ovarian function and prevented oestrous behaviour. These effects were reversible and the subsequent fertility of the vaccinated fillies was normal. 相似文献
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Objective To determine the reliability of collecting serial 4-mL blood samples over 13 h using a 20-gauge, cephalic catheter in conscious dogs. Design Prospective, observational study. Animals Twelve (6 males, 6 females) healthy, neutered, lean dogs. Procedure Percutaneous placement of a 20-gauge, 1.1 × 30 mm intravenous over-the-needle catheter into the cephalic vein was performed in each dog on three occasions. Catheter patency was maintained by intermittent flushing with 0.9% saline and 1 IU/mL heparinised saline solutions. Blood samples (4 mL) were obtained at 10 time-points over 13 h, with close monitoring of the dogs and the indwelling catheters. Blood volume, resistance on aspirating blood sample (minimal or marked resistance) and the methods used to improve blood flow were recorded. Results A high proportion (93%) of blood sample collections achieved the required 4-mL volume, and the remaining samples were greater than 1.5 mL. Of the 358 collections via the cephalic catheter, 311 (87%) were obtained with ‘minimal resistance’. The remaining collections had ‘marked resistance’ (n=47) and were associated with a loose catheter in 11% (5/47) and of unknown cause in 89% (42/47). After ‘marked resistance’ had been encountered and the catheter was flushed with saline and heparin solutions, subsequent sampling with ‘minimal resistance’ was frequently possible from the same catheter. Conclusion Use of a percutaneous, 20-gauge intravenous cephalic catheter allowed reliable serial collection of 4-mL blood samples over 13 h in conscious dogs. 相似文献