[The spread of enzootic bovine leukemia via the seminal fluid in certain breeds of bulls].

Studied was the occurrence of enzootic bovine leukosis as dependent on the use of semen of leukosis-affected bulls for the artificial insemination of cows and heifers and their offsprings in the F1 generation on 16 farms. Semen was used of a total of 30 bulls of the Holstein-Friesian, American Brown, and European Black-and-white breeds. The agar gel immuno-diffusion test was employed to establish antibodies to the bovine leukosis virus in the sera of the bulls.

[Effect of coccidiostats on the quality of the immune response following the vaccination of chickens against Newcastle disease].

An experiment was carried out to test the effect of two coccidiostatica, amprol and monensin, on the level of the Newcastle disease anti-hemagglutinins. The study made use of broiler chickens of a four-line hybrid (Plymouth Rock x Cornish) treated with a Hitchner B vaccine. The drugs were admixed with the feed--amprol at the rate of 0.

[Comparative studies of blood sera and lactosera by agar gel precipitation (AGP) in enzootic leukemia in cows].

Studied were a total of 70 samples of blood and corresponding lactosera taken from lactating cows that were positive for leukosis on three farms with records for the disease. The lactosera were obtained from the milk samples through treatment in two ways--with calcium chloride and with chymosin. The experiments were carried out with untreated blood sera and with the lactosera obtained in both ways.

[Effect of levamisole on the level of antihemagglutinins, serum sialic acid and lysozyme in the aerosol vaccination of chickens against Newcastle disease].

Tested was the effect of the levamisole antihelminthic on the dynamic of anti-hemagglutinins, serum sialic acid, and lysozyme in the process of building active immunity against Newcastle disease following aerosol vaccination. It was found that there was unidirectional correlation of the active immunologic process with the level of serum sialic acid and lysozyme. The use of levamisole in adequate doses, applied opportunely enhanced the unspecific humoral defense of the body, having no direct influence on the quality of actively built specific immunity.

[Changes in the amount of serum sialic acid in the vaccination of poultry against Newcastle disease].

A total of fifty birds of a four-line hybrid (Plymouth X Cornish) were used in an experiment to elucidate the link between the dynamics of serum sialic acid and the level of antihemagglutinins prior to and after vaccination against Newcastle disease (ND). It was found that immediately after vaccination the level of serum sialic acid rose essentially, and persisted at high values in the course of 7-8 days. It came back to the initial level at the time when the ND antihemagglutinins showed a maximum rise, i.

[Production of a polyglobulin preparation against respiratory diseases in calves].

On the basis of literature data concerning the production of polyglobulins from animal sera with the employment of appropriate, short term methods, and using the author's personal experience a method was tested for the production of specific polyglobulins against the respiratory complex in calves. A particular scheme was used for the purpose, hyperimmunizing adult cattle with killed vaccines against parainfluenza-3, adenoviruses 1 and 3, and IBR. The hyperimmune serum obtained was further treated by the etanol short term method to produce a high-titer polyglobulin.

[Study of the effect of some of the vaccination plans applied in Bulgaria against Newcastle disease].

Comparative studies were carried out on the effect of the vaccination of broilers against Newcastle disease with La Sota strain through the single application in the drinking water on the 21st day and the newly introduced vaccination at the age of four days, using the spray method, as well as the combined method--spray vaccination on the fourth day and giving the vaccine twice on the 21st day. It was found that the last method confers better immunity and higher immunity against the disease as compared to offering the vaccine only once on the 21st day.

[Agar gel diffusion precipitation and immunoelectrophoresis of the Aujeszky virus].

Two virulent and two vaccinal virus strains are dealt with. The study has been carried out by means of the diffusion precipitation reaction in agar gel and the immunoelectrophoresis technique using hyperimmune sera obtained from cocks as well as concentrated and purified antigens. It has been demonstrated that the virulent and the vaccinal (latent) strains of Aujeszky's disease virus cannot be differentiated serologically.

[Use of temperature, trypsin and biological tests for the intraspecies differentiation of local strains of Aujeszky's disease virus].

Studies were carried out with 8 strains of Aujeszky's disease virus using a temperature test (50 degrees C for 1 hour), a trypsin test (0.5 mg per cu. cm at 37 degrees C 1 hour), and a biologic test.

[Study of the symplast-forming activity of terpene and standard strains of Aujeszky's disease virus].

Studied were the cellular changes and, more specifically, the production of symplasts as a particular form of manifesting the cytopathic effect of some strains of the Aujezsky's virus. Experiments with eight strains of the virus in tissue cultures confirmed the concept of a number of authors that in given tissue cultures virulent strains show a well pronounced trent toward the formation of symplasts containing numerous nuclei, while the latent strains stimulate the production of sporadic, rounded giant cells with a few nuclei in the aggregated cytoplasm. In the course of the investigations the primary cultures of rabbit kidney proved very suitable to demonstrate the presence of Aujeszky's disease and differentiate latent and virulent strains because of the cultures exceptional receptivity to the Aujeszky virus.