Penetration Resistance,Root Growth,and Water Content in a Subsoiled Claypan1

Penetration resistance, root length density, and water content of soil with maize (Zea mays L.), soybean (Glycine max [L.] Merr.), or a mixture of alfalfa (Medicago sativa L.) and fescue (Festuca arundinacea Schreb.) were measured during two summers, one of which was dry. Plants grew on a silt loam (Mollic Albaqualfs; fine, mixed, thermic), 0.25 m deep overlying a claypan, 1.75 m thick. Half of the plots were subsoiled before planting in the first year of the study and the other half were not subsoiled. During both years, subsoiling had no measurable effect in lowering the penetration resistance in the claypan. Root length density was greater in the claypan than in the topsoil. Subsoiling did not increase root length density in either year. Water content in plots that had been subsoiled was usually similar to that in plots that had not been subsoiled. In the dry year, roots of maize proliferated more in the claypan than did roots of soybean or alfalfa + fescue.     

Epidemiology of Equine Protozoal Myeloencephalitis in North America Based on Histologically Confirmed Cases

Following a workshop on equine protozoal myeloencephalitis (EPM) convened at the Veterinary Medical Forum of the American College of Veterinary Internal Medicine in 1988, this survey of EPM in North America was developed. It is based upon 364 histologically confirmed case records from California, Florida, Illinois, Kentucky, New York, Ohio, Oklahoma, Ontario, Pennsylvania, and Texas up to 1988. The highest rate of infection was found in young Thoroughbred, Standardbred, and quarter horses. Differences in geographic location, sex, and month (season) of infection were not discernible. This report, the first comprehensive survey of EPM in North America, is intended to serve as a basis for evaluating future changes in prevalence and spread of EPM.     

Laboratory evaluation of malassimilation in horses

Malassimilation should be suspected in horses with weight loss in spite of a good appetite. Malassimilation is usually confirmed with oral glucose or D-xylose absorption tests, whereas the oral lactose tolerance test can be used to evaluate lactase deficiency in foals. Once malassimilation is confirmed, other diagnostic tests such as abdominocentesis, rectal mucosal biopsy, or exploratory laparotomy with intestinal biopsies may determine the etiology of malassimilation.     

Compression bone plating of a medial condylar fracture of the third metatarsal bone in a Thoroughbred filly

A medial condylar fracture of the third metatarsal bone in a 2-year-old Thoroughbred filly was repaired successfully by use of compression bone plating. At discharge from the hospital, thickening of the metatarsus was evident, and proliferative changes were associated with the site of bone plate application. It was expected that these changes would limit the filly's use as a racehorse, and a return to training was not recommended. Especially in horses that may return to racing, use of compression bone plating initially should not replace stall rest or lag screw fixation treatment of this type of injury. However, the use of a similar approach in selected cases of medial condylar fracture of the third metatarsal bone is encouraged, especially when additional fissure lines are evident on radiographs.     

Comparison of the mucosal immune response in dogs vaccinated with either an intranasal avirulent live culture or a subcutaneous antigen extract vaccine of Bordetella bronchiseptica

Healthy dogs with low antibody titer to Bordetella bronchiseptica were vaccinated intranasally with an avirulent live vaccine, subcutaneously with an antigen extract vaccine, or subcutaneously and intranasally with a placebo. Intranasally vaccinated dogs developed B. bronchiseptica-specific IgA titers in nasal secretions that remained at high levels until the end of the study; dogs vaccinated subcutaneously with the antigen extract or placebo did not develop measurable antigen-specific IgA titers in nasal secretions. Dogs were challenged with virulent live B. bronchiseptica 63 days after vaccination. Intranasally vaccinated dogs had significantly lower cough scores (P < or =.0058) and shed significantly fewer challenge organisms (P <.0001) than dogs in either of the other groups. Cough scores of subcutaneously vaccinated dogs were not significantly different from placebo-vaccinated dogs.     

Experimental challenge models for Johne's disease: a review and proposed international guidelines

An international committee of Johne's disease (JD) researchers was convened to develop guidelines for JD challenge studies in multiple animal species. The intent was to develop and propose international standard guidelines for models based on animal species that would gain acceptance worldwide. Parameters essential for the development of long-term and short-term infection models were outlined and harmonized to provide a "best fit" JD challenge model for cattle, goats, sheep, cervids, and mice. These models will be useful to study host-pathogen interactions, host immunity at the local and systemic level, and for evaluating vaccine candidates and therapeutics. The consensus guidelines herein list by animal species strains of Mycobacterium avium subsp. paratuberculosis used, challenge dose, dose frequency, age of challenge, route of challenge, preparation of inoculum, experimental animal selection, quality control, minimal experimental endpoints and other parameters.     

Surface Deformation and Lower Crustal Flow in Eastern Tibet

Field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern Tibetan plateau since about 4 million years ago. Instead, central eastern Tibet has been nearly stationary relative to southeastern China, southeastern Tibet has rotated clockwise without major crustal shortening, and the crust along portions of the eastern plateau margin has been extended. Modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle. This model also predicts east-west extension on the high plateau without convective removal of Tibetan lithosphere and without eastward movement of the crust east of the plateau.     

Estimating the mass of asteroid 253 mathilde from tracking data during the NEAR flyby

The terminal navigation of the Near Earth Asteroid Rendezvous (NEAR) spacecraft during its close flyby of asteroid 253 Mathilde involved coordinated efforts to determine the heliocentric orbits of the spacecraft and Mathilde and then to determine the relative trajectory of the spacecraft with respect to Mathilde. The gravitational perturbation of Mathilde on the passing spacecraft was apparent in the spacecraft tracking data. As a result of the accurate targeting achieved, these data could be used to determine Mathilde's mass as 1.033 (+/- 0.044) x 10(20) grams. Coupled with a volume estimate provided by the NEAR imaging team, this mass suggests a low bulk density for Mathilde of 1.3 grams per cubic centimeter.     

Proton alleviation of growth inhibition by toxic metals (Al, La, Cu) in rhizobia

Free-living rhizobia are sensitive to soils and artificial media that are acidic. Both excessive H⁺ and Al released from acid-soluble minerals appear to be toxic. The complex, heterotrophic nutrient requirements of rhizobia and the joint occurrence of Al³⁺ and hydroxo-, sulphato-, phosphato-, fluoro-, and other Al species have prevented a precise attribution of toxicity to the Al species. In the present study, a medium composed of 0.3 mM MgSO₄, 2 mM CaCl₂, and 10 mM sucrose (the basal medium) enabled a 1000-fold cell increase at pH 4.6 or above. Additions of 1 μM AlCl₃ to the basal medium were highly intoxicating, especially at higher pH: below pH 5.0 cell numbers increased slightly; at pH 5.0 cell numbers did not change from the inoculum; at higher pH values the cell numbers declined. Similar trends were observed for La³⁺ and Cu²⁺ intoxication. Uptake of methylene blue, a positively charged dye useful as a probe of cell-surface electrical potential, was inhibited by pH reductions between pH 3.5 and 6.0. Factors that decrease cell-surface negativity (such as lower pH) reduce the intoxication by cations in plant roots, but the pH responsiveness of the rhizobia in our system was much greater than the pH responsiveness of plants. Although plant-root intoxication by mononuclear hydroxo-Al species has been discounted, rhizobia may be sensitive to those species. These results have implications for the management of rhizobia in acidic soils and for the development of resistant strains.