Effects of α2-adrenergic drugs on blood platelets in sheep

Xylazine (0.2 mg/kg, iv) alone or preceded by atipame-zole (0.125 μg/kg, iv) or by aspirin (10 μg/kg, iv) was administered to 18 sheep. Medetomidine (60 μg/kg, iv) was also administered to 12 sheep. Xylazine, but not medetomidine, significantly reduced the number of platelets. Both atipamezole and aspirin prevented this reduction. It was concluded that α₂-agonists would seem to produce platelet aggregation that may contribute to the development of the respiratory changes that follow the administration of α₂-agonists in sheep, but probably not always to a degree that could result in a significant decrease in the number of circulating platelets.     

Measurement of nitrate leaching losses from arable plots under different nitrogen input regimes

Abstract. Leaching losses of nitrate-nitrogen were measured from a set of eight hydrologically isolated plots on a clay loam soil over the period from September 1987 to February 1990. Variable drainflow recovery from the plots hampered accurate estimation of nitrate loading, but results suggest that, when inorganic nitrogen fertilizer is applied up to the recommended amount, there is little influence of the amount applied on the amount leached. We did, however, observe the following effects on nitrate leaching: leguminous green manure incorporated in autumn increased leaching of nitrate-nitrogen by 10–15 kg per hectare during the winter; autumn cultivation caused some increase in leaching compared with no cultivation in one year; some systematic variations in nitrate leaching occurred between years and between plots, but were unrelated to treatments.
From the results we conclude that green manuring does not provide sufficient nitrogen for organically grown crops on this soil but contributes significantly to nitrate leaching, and that growing spring cereals, with the land remaining in stubble as long as possible in autumn, may be the best strategy to minimize nitrate leaching.     

Salinity Effects on the Growth and Ion Contents of Some Chickpea (Cicer arietinum L.) and Lentil (Lens culinaris Medic.) Varieties

The effect of salinity on seed germination, plant yield parameters, and plant Na, Cl and K concentrations of chickpea and lentil varieties was studied. Results showed that in both crops percentage emergence was significantly reduced by increasing NaCl levels (0–8dSm^?1). From the plant growth studies it was found that differences existed among chickpea and lentil varieties in their response to NaCl application. In chickpea, the variety Mariye showed the comparatively lowest germination percentage and the lowest seedling shoot dry weight in response to salinity and was also among the two varieties which had the lowest relative plant height, shoot and root dry weight and grain yield at maturity. Similarly, variety DZ-10-16-2, which was the second best in germination percentage and the highest in terms of seedling shoot dry weight, also had the highest relative plant height, shoot and root dry weights, and grain yield at maturity. In lentil, however, such relationships were less pronounced. Chloride concentration (mg g^?1) in the plant parts at salt levels other than the control was about 2–5 times that of Na. K concentration in the plants was significantly reduced by increasing NaCl levels. Chickpea was generally more sensitive to NaCl salinity than lentil. While no seeds were produced at salinity levels beyond 2dSm^?1 in chickpea (no seeds were produced at this salt level in the most sensitive variety, Mariye), most lentil varieties could produce some seeds up to the highest level of NaCl application. Overall, varieties R-186 (lentil) and Mariye (chickpea) were the most sensitive of all varieties. On the other hand, lentil variety NEL-2704 and chickpea variety DZ-10-16-2 gave comparatively higher mean relative shoot and root dry weights, and grain yield, thus showing some degree of superiority over the others. The observed variations among the varieties may be useful indications for screening varieties of both crops for salt tolerance.     

The significance of the structural characteristics of the agent for the problems of immunization against blue tongue]

Bluetongue virus (BTV), an arthropod-borne virus, is transmitted primarily by biting midges of the genus Culicoides. Some insect species, which might serve as a potential vector, are prevalent in Central Europe. In sheep, bluetongue is acute and mortality is high, whereas in cattle, goats and most wild ruminants the infection is usually clinically inapparent. Viremia is of short duration in sheep, but cattle experience a prolonged viremia and provide a reservoir for the dissemination of BTV. At least 24 different BTV serotypes have been identified. Antigenic variations occur in the polypeptides of the outer viral capsid and the segmented nature of the viral genome provides the potential for evolution of the virus by a mechanism of reassortment. This renders the use of polyvalent vaccines inefficient and emphasizes the significance of import/export restrictions on ruminants from BTV endemic areas.     

Deforestation patterns and their effects on forest patches

Five identifiable patterns of deforestation are recognized - internal, indentation, cropping, fragmentation, and removal - and each has a distinct effect on habitat quality of forest patches in the eastern United States. By overlaying land use maps from 1973 and 1981 for three counties in the State of Maryland (Prince Georges, Anne Arundel, and Wicomico), changes in the interior core area and edge length of individual patches were measured. Forest interior declined by 23.8 km² in Anne Arundel, 16.3 km² in Prince Georges, and 8.4 km² in Wicomico. Within Anne Arundel and Prince Georges Counties, deforestation increased edge length by 52.1 km and 31.2 km, respectively, whereas, within Wicomico, it decreased edge length by 8.7 km. Differences among counties resulted from current land use patterns, percentage of forest cover, and the dominant deforestation pattern.     

Prototype agricultural land evaluation systems for Canada: I. Overview of systems development

Abstract. Information on land resources and the capacity of land to support agricultural production is a prerequisite for the formation of sound agricultural policies. This paper summarizes Canadian experiences in developing national and regional land evaluation systems. Potential users expected the system to estimate the degree to which changes in biophysical and socio-economic conditions would alter options for land use and production, and to provide a context for more detailed analysis.
A broad-scale land evaluation system was designed to serve the needs identified by representative user groups. Two prototype systems were developed from available information to test the major features of the system design. Neither prototype was complete; one was national in extent and capable of addressing issues of national and provincial importance, the other covered a sub-provincial area but allowed for more detailed evaluation of the effects of soil modifying processes. A full range of applications was demonstrated using one or other of the prototype systems. As a result of this project, the broad-scale land evaluation system design was improved and verified, ongoing research and data collection activities were adjusted to ensure that they meet the needs of a macroscale land evaluation system, and approaches were developed to overcome problems of land evaluation system development.     

Quantitation of adenine nucleotides in equine colonic mucosal tissue using high performance liquid chromatography.

The objectives were to use high performance liquid chromatography (HPLC) to validate an established method for adenine nucleotide separation in equine colonic mucosal tissue, to determine the inherent variability in the tissue and extraction method, and to determine the stability of ATP, ADP, and AMP in the tissue with time. Equine colonic mucosal tissue obtained from a single horse was immediately submersed in liquid nitrogen, and stored at -70 degrees C. Samples were lyophilized, extracted, and separated by HPLC. The limit of quantitation was 0.05 microg/mL. The coefficient of variation for the instrument was less than 10% for all nucleotides measured. When the tissue was not homogenized prior to sampling, there were significant differences in adenine nucleotide content between samples. However, when the tissue was homogenized prior to analysis, these differences were no longer significant. There was no significant decrease in ATP, ADP, or AMP content over a 54-day analysis period.     

Transmission of porcine reproductive and respiratory syndrome virus from persistently infected sows to contact controls.

The objective of this study was to determine if porcine reproductive and respiratory syndrome virus (PRRSV) could persist in non-pregnant sows and if persistently infected sows could transmit virus to naive contact controls. Twelve PRRSV-naive, non-pregnant sows (index sows) were infected with a field isolate of PRRSV and housed in individual isolation rooms for 42 to 56 days postinfection. Following this period, 1 naive contact sow was placed in each room divided by a gate allowing nose-to-nose contact with a single index sow. Index sows were not viremic at the time of contact sow entry. Virus nucleic acid was detected by polymerase chain reaction, and infectious virus was detected by virus isolation in sera from 3 of the 12 contact sows at 49, 56, and 86 days postinfection. All 3 infected contacts developed PRRSV antibodies. Virus nucleic acid was detected in tissues of all of the 12 index sows at 72 or 86 days postinfection. Nucleic acid sequencing indicated that representative samples from index and infected contacts were homologous (> 99%) to the PRRSV used to infect index sows at the onset of the study. This study demonstrates that PRRSV can persist in sows and that persistently infected sows can transmit virus to naive contact animals.