Improvement of Fertility in Artificially Inseminated Ewes Following Vaginal Treatment with Misoprostol Plus Terbutaline Sulphate

The effect of vaginal administration of misoprostol plus terbutaline sulphate 6 h prior to artificial insemination (AI) upon the site of AI (vaginal or cervical) and fertility was studied using a total of 87 estrous synchronized Serra da Estrela ewes (control n = 42 and treated n = 45). Artificial insemination was performed using refrigerated semen at 54–55 h after sponge removal. Lambing rate (fertility) and prolificacy were compared between control and treated ewes. The effect of the site of semen deposition on fertility was also evaluated. Prolificacy rate was not different between control (1.5) and treated (1.59) ewes. The proportion of cervical AI achieved in control (45.2%) and treated (37.8%) ewes was not significantly different. Overall, fertility was significantly lower in control than in treated ewes (42.9% vs 64.4%; p < 0.04). Fertility following vaginal AI was significantly lower for control for than treated ewes (30.4% vs 60.7%; p < 0.03) but the difference was smaller and not significant for cervical AI (control 57.9% vs 70.6%). It was concluded that vaginal administration of misoprostol plus terbutaline sulphate 6 h prior to artificial insemination did not affect the proportion of cervical inseminations but significantly improved the fertility of treated ewes. Although needing confirmation, it was hypothesized that drugs might have induced local secretory modifications leading to an increase of cervical ability to retain more viable spermatozoa for fertilization.     

Modeling Adaptive Mutation of Enteric Bacteria in Surface Water Using Agent-Based Methods

Mechanistic models of enteric bacteria fate and transport in surface waters are important tools for research and management. The existing modeling approach typically assumes that bacteria die in a first-order fashion, but a recent study suggests that bacteria can mutate relatively rapidly to a strain better adapted to the surface water environment. We built an agent-based model that simulates individual wild-type and mutant Escherichia coli cells. The bacteria die, grow on the natural assimilable organic carbon available to E. coli, divide and mutate. We apply the model to laboratory experiments (from the literature and new ones) and the Charles River in Boston. Laboratory applications include decay, growth, and competition (between wild-type and mutant) in various types of surface water. For decay experiments, the stochastic mutation process in the model can produce both first-order and biphasic decay patterns, which is consistent with observations in the literature. For the Charles River, the model can reproduce the main patterns observed in the field data. The model applications provide evidence in support of the mutation mechanism. However, the mutation model does not produce better predictions for the Charles River than a previous model based on labile and resistant subpopulations.     

The Effect of Calcium Sprays and Fruit Thinning on Bitter Pit Incidence and Calcium Content in ‘Honeycrisp’ Apple

‘Honeycrisp’ is a recently released cultivar of apple (Malus x domestica) developed by the University of Minnesota, now in high demand by growers and consumers. This cultivar is susceptible to bitter pit, especially when the trees are young and the fruit load is low. The effects of calcium (Ca) sprays, fruit thinning, vegetative growth, fruit and leaf nutrient concentration on bitter pit incidence, and two sampling methods for nutrient analysis were studied. Bitter pit incidence was associated with several variables, including Ca and phosphorus (P) concentrations in leaves and fruits, magnesium (Mg) concentration in leaves, and yield parameters. Fruit Ca concentration and content for the growing season were modeled, which allowed the determinations of Ca levels associated with bitter pit incidence. Our data suggest that plug analysis was less sensitive than fruit-segment analysis for finding differences in Ca concentrations.     

带拉杆的U形壳槽槽身横向内力计算有关问题的分析

在U形壳槽横向内力计算中,若不考虑槽底局部加厚对Φ=90°截面内力的影响,则计算所得的该截面弯矩绝对值偏小.温度变化对截面内力的影响较大,特别是温降引起多数截面的弯矩增加,而轴向力减少;温升引起Φ=90°截面弯矩与轴向拉力均增加,再考虑槽底局部加厚的影响,弯矩值还要增加.槽底局部加厚与温度变化的作用均不能忽略不计,否则,内力计算成果值会偏于不安全.用结构力学方法,推导出二者对内力影响的计算公式,并附有应用的算例.     

Defining competition vectors in a temperate alley cropping system in the midwestern USA: 1. Production physiology

With renewed interest in the use of ecologically-designed, sustainable agricultural systems for temperate regions of the world, agroforestry is being proposed as an alternative to intensive production of crops in monocultures. However, the knowledge-base for understanding and managing complex, multi-strata systems worldwide is limited, particularly so for temperate regions. We examined an alley cropping system in the midwestern US where maize (Zea mays L.) is grown in alleys between tree rows of either black walnut (Juglans nigra L.) or red oak (Quercus rubra L.). During a course of ten years, crop yields in rows adjacent to tree rows declined by 50% or more. With the experimental introduction of barriers to separate tree and crop root systems, yields in the rows near trees were equal to those of the center row (and monoculture). Irrespective of a high correlation between photosynthetically active radiation and net photosynthesis, shading did not have a major influence on crop yield. At this stage of system development (11 year old trees), influence of incident PAR on crop yield seems to be minimal. Subsequent papers in this series examine the sharing of belowground resources between trees and crops to quantify the competitive interactions that impact crop yields and their implications for economic return to the farmer.This revised version was published online in November 2005 with corrections to the Cover Date.