Experimental and natural infection with the enzootic leukosis virus of cattle

A trial was performed with heifers at the age of six to seven months. The animals were experimentally infected with the lymphocytes of a virus-productive donor. Infection was produced in all the nine cases, as demonstrated by means of the positive syncytial test. As indicated by the results of the trial, the antibodies to the enzootic bovine leucosis virus (BLV) were produced soon after experimental infection. A high sensitivity of the serum-neutralization test and the ELISA method was demonstrated in this connection: by these methods, the antibodies were identified already two to three weeks after experimental infection whereas by the immunodiffusion test they could be detected only after five weeks. Twenty-four animals were exposed to natural contact infection. Within 270 days of the trial, the disease after contact was recorded only in one heifer out of the four that were in close contact with the experimentally infected animals. In this case, as compared with experimental infection, the antibodies were produced much later--after 85 to 93 days. Leucosis was recorded in none of the remaining animals. The reasons why such a favourable result was obtained were the thorough disinfection of the stables after blood collections and the strict observance of the aseptic conditions. The results of experimental infection in three cows were identical with those obtained in young cattle. In the experimentally infected dairy cows, antibodies in milk were determined by the ELISA method. As found, in milk the antibodies to BLV appear two to three weeks later than they do in serum. The ELISA method of BLV antibody detection can be used for the identification of infected animals in herds where enzootic bovine leucosis occurs.     

The impact of the Department of Phytopathology at the Wageningen Agricultural University, as evaluated by citation analysis

The results of a citation analysis of all publications by the Department of Phytopathology which appeared in the period 1969–1987, but based on citations recorded by the Science Citation Index only, are presented. Together with the results of an analysis of self-citations by the eight most cited authors they suggest, that phytopathology as a science is poorly covered by the Science Citation Index.Een citatie-analyse van alle in de periode 1969–1987 verschenen publikaties van de Vakgroep Fytopathologie omvatte uitsluitend citaties voorzover vermeld in de Science Citation Index (SCI).Enkele vermeldenswaardige resultaten betreffen de krommen, die de cumulatieve citatie-aantallen weergeven (Figuren 1b en 2b) en de grafiek, die de relatieve bijdrage van uiteenlopende publikaties aan het totaal der citaties uitbeeldt (Fig. 3). Uit Fig. 2b blijkt, dat het citatieverloop van een gemiddelde publikatie het karakter van een logistische groeikromme vertoont: na een lagfase en een fase van exponentiële groei vlakt de kromme at naar een stationaire fase. Uit Fig. 3 kan worden afgeleid, dat weinig artikelen veel, en vele weinig tot het totale aantal citaties bijdragen; zo nemen 25 van de in totaal 321 geciteerde artikelen 50% van het totale aantal (3659) citaties voor hun rekening!     

Efficacy of a mephentermine‐based product as a vasopressor and a cardiac performance enhancer when given intramuscularly to cattle

The goal of this study was to confirm the vasopressor and cardiac effects of POTENAY^® INJETÁVEL (POT), a mephentermine‐based product, given to cattle with induced vascular/cardiac depression. Ten healthy Holstein cattle (206 ± 13 kg) followed a randomized‐complete‐block design (RCBD) utilizing crossover study design. Each animal randomly received (1 ml/25 kg, IM) of either POT (n = 10) or volume‐matched placebo control (0.9%NaCl, CP, n = 10). A subset of animals (n = 5) received POT first (day 0) while the remaining (n = 5) received CP; after a six‐day washout period, cattle received the opposite compound. Animals were anesthetized and catheterized for systemic/left ventricular hemodynamic monitoring. Myocardial dysfunction/hypotension was induced by increasing the end‐tidal isoflurane concentration until arterial blood pressure was 20% lower than at baseline and remained stable. Once the animal was determined to be hypotensive and hemodynamically stable, steady‐state hypotensive baseline data (BL2) were acquired, and treatment with either POT or CP was given. Data were acquired post‐treatment at every 15 min for 90 min. POT improved cardiac output (+68 L/min, ±14%, p < 0.05), MAP (+14 mmHg, ±4%, p < 0.05), HR (+22 bpm, ±8%, p < 0.05), and peak rates of ventricular pressure change during both systole (dP/dt_max: +37 mmHg/s ±13%, p < 0.05) and diastole (dP/dt_min: +31 mmHg/s, ±7%, p < 0.05). No improvements were noted following placebo‐control administration. Results indicate that POT improves cardiac performance and systemic hemodynamics in cattle with induced cardiovascular depression when given as single intramuscular injection.     

Evaluation of the effectiveness of selected measures against bovine spongiform encephalopathy (BSE) in Switzerland by use of the basic reproduction ratio R0

The effectiveness of two measures against Bovine Spongiform Encephalopathy (BSE), the compulsory processing of animal by products to meat and bone meal (MBM) at 133 degrees C under 3 bars of pressure for 20 minutes in February 1993 and the exclusion of fallen stock, heads with eyes and spinal cord of cattle older than 30 month from MBM production in April 1996, was evaluated in a process model. The transmission of BSE by calculation of the basic reproduction ratio R0 was modelled.The results were verified by use of a cohort model, based on observed surveillance data. Prior to 1990, before the ban of feeding MBM to ruminants, R0, as calculated in the process model, was above 1, coherent with a slowly progressing BSE epidemic. Since 1991, values of R0 were low at 0.06.The corresponding R0 values derived from the cohort model were higher, the lowest value 0.13 calculated for 1996. Given such low R0 values, the epidemic should have died out. Additionally, no influence of the two measures was obvious at that time given the low level of R0. The discrepancy between the results of the two models is evidence for a dependency of the BSE epidemic from an infection source not considered in the process model. This infection source is most likely importation of feed ingredients and MBM.     

Determining transpiration from meteorological data and crop characteristics for irrigation management

Summary Traditional meteorological estimates of evapotranspiration include empirical crop factors which are inadequate for scheduling high frequency irrigation. The performance of a transpiration model was tested and adapted to suit the operational requirements of automated irrigation systems. Hourly measurements of global solar radiation, air temperature, humidity and wind speed, obtained from an automatic weather station are inputs to the model. Additional inputs include daily updated data of plant height and leaf area index. This information is processed to determine the active coupling surface between the crop and the atmosphere. The model takes into account the resistance of the leaf to diffusion of water vapor.Calculated transpiration, based on the model, matched very closely measurements of latent heat flux in an irrigated cotton field. It was also in good agreement with water uptake measured in stems of the cotton plants using a heat pulse technique. The test also showed that implementation of the model in the field under study would have improved the efficiency of water application.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 1855-E, 1986 series     

Stability and Biological Activity of Cyfluthrin Isomers

A GC-MS method capable of completely separating the four pairs of diastereoisomers of cyfluthrin is presented and the method used to show that isomerisation of the cyfluthrin enantiomers occurs in methanol. This methanol-induced isomerisation could also be demonstrated by bioassays using water fleas. The biological activities of the various cyfluthrin isomers contained in the commercial products cyfluthrin and beta-cyfluthrin were assayed using several strains of lepidopteran larvae including Plutella xylostella, Heliothis virescens and Spodoptera frugiperda. With the susceptible strains, the efficiencies of the isomers mixtures of cyfluthrin and beta-cyfluthrin were shown to obey the rules of additivity. However, in tests with a resistant strain of P. xylostella originating from Thailand, the ‘inactive’ isomer III acted synergistically with the active isomer IV. Resistance factors in strains of H. virescens and P. xylostella were found to be higher with cis than with trans isomers. This probably contributes to the superior action of cyfluthrin and beta-cyfluthrin against various pests of agricultural importance since the commercial products contain a high content of trans isomers (‘high trans pyrethroids’).