Investigation of morphological changes in bone marrow of young hens in the conditions of application of associated virus vaccines and sodium thiosulphate immunostimulant was realized in the Republic of Belarus. The associated virus vaccine was applied against infectious bursal disease, infectious bronchitis, infectious laryngotracheitis, and Newcastle disease. Research results showed that under the influence of inactivated vaccine against mentioned above diseases there was noted the increasing of quantity of granulocytic cells, there was stated an active hyperplasia of pseudoeosinophil cells. Immunization of young hens with the presented vaccine developed in the Institute of Experimental Veterinary Medicine of the National Academy of Sciences of Belarus promoted a short-term increasing of leucoerythroblastic index. Application of an alternative vaccine developed by Scientific and Production Enterprise Avivak did not render substantial influence on the morphology of bone marrow of chickens. Sodium thiosulphate applied in combination with associated vaccines (in 7% concentration in vaccine) caused the hyperplasia of lymphoid and thrombocyte cells, strengthened the proliferation and maturity of granular leukocytes

Influence of monocalcium phosphate on natural resistance and clinical indexes of blood of breeding bull calves of white-and-black breed was realized in the conditions of the Republic of Belarus. Bull calves of the first (control) group in the composition of their main ration were fed with mixed fodder K-66-b, hay, green mass and as a balanced phosphoric-potassium additive they were fed with8 grams of defluorinated phosphate per 1 kg of mixed feed. Bulls of the second, third and fourth experimental groups in combination with the standard ration instead of difluoridated phosphate were fed with 5; 10; and 15 grams monocalcium phosphate per 1 kg of combined feed, respectively. Research results showed that application of fodder monocalcium phosphate in addition to the main ration made it possible to increase calcium and phosphorus content in blood of experimental bull calves. In the control group phosphorous content was 2,17 micromole, in the experimental groups – 2,40-2,78 micromole; calcium content – 2,50 and 2,58-2,88 micromole, respectively. The analyzed additive rendered positive effect on protein exchange, increased the natural resistance, bacterial growth-inhibitory activity in blood serum in the third, fourth and second groups on 50,3%, 42,5%, and 40,3%, respectively; lysozyme activity – on 46,0%, 39,2%, and 32,3%, respectively; phagocytic activity of leukocytes – on 21,9%, 25%, and 19,1%

Immunomorphological changes in young hens vaccinated with an associated inactivated emulsion vaccine against bursal disease, infectious bronchitis and Newcasle disease was realized in the conditions of the Republic of Belarus. Replacement young hens of 130-158 days old were divided into 2 groups with 200 head in each according the analogue principle. At the age of 130 days old the first experimental group of chickens was immunized against bursal disease, infectious bronchitis and Newcasle disease with a liquid inactive emulsion vaccine (produced in the republic of Belarus) in dose of 0,5 ml intramuscularly. In course of the experiment chickens from each group were killed on the third, seventh, fourteenth, twenty-first and twenty-eighth days. For the analysis of immunomorphological reaction there were tested tissue pieces from the places of vaccine administration, as well as thymus, bursa of Fabritius, lien, cecal tonsils and Garder's gland. Research results showed that in tissues in places of the vaccine administration there were developed hemorrhages, serous inflammatory edema, necrobiosis and necrosis of muscular fibers, inflammatory cellular infiltration, and moderate plasmocytic reaction. At a later stage at the places of damaged structures there was noted the development of granulation tissue with presence of some lymphoid nodules. In response to vaccination in the central organs of poultry immunity there was stated the sinuated changes of morphological indexes. Immunization of chickens against infectious bursal disease, infectious bronchitis and Newcasle disease promoted the increasing of absolute weight of lien, activation of blastic and plasmocytic reaction in bursa of Fabritius and lien and did not render substantial influence on immunomorphological indexes of cecal tonsils and Garder's gland

Selection of an optimal dose of Cryptosporidium parvum agents which were isolated from swine and could cause expressed changes in organs of experimentally infestated mice was realized in the conditions of the Republic of Belarus. Data about on persistence of homoxenous coccidia Cryptosporidium parvum at laboratory white mice and pathomorphological changes in the bodies of experimental animals were presented. In a mucous coat of intestines there was marked a catarrhal inflammation with mucous membrane necrosis and its infiltration by leukocytes and macrophages.

After the pathomorphological and histological studies of innards of fallen experimental animals in all realized experiments it was found that sheep and lambs infected with pneumoviral infections (Parainfluenza-3, Adenoviridae, respiratory streptococcosis infection) with their additional infestation with radioactive substances there was stated the acceleration of infectious process, and disease recrudesced up to 2-5 and more times (depending on irradiation doze). The immunity of sheep and lambs decreased caused by reproduction of viruses, and in acute cases animals died but in cases of mild forms the disease transformed into chronic form and caused animal death.

Research results showed that in the conditions of correct organization and application of technological methods of livestock breeding and feeding it was possible to achieve high livability rate of sheep and lambs up to 90%. Also it was possible to get a substantial break of infection chain of many sheep diseases (especially those which had a respiratory nature). Research results showed that simultaneous application of convalescent-phase serum against sheep acute respiratory diseases, as well as Nitox 200 and Invamek for treatment of sheep and especially 2-3 month old lambs with respiratory infectious diseases promoted the recovery of 80-100% of animals.

It was established that in blood serum of pigs vaccinated against leptospirosis there was an authentic increasing of alanine aminotransferase, alkaline phosphatase and gamma-glutamyltransferase that made proved the presence of residual reactogenicity of biological preparations. In course of the experiment there were used 4 groups of swine which were administrated with 4 types of vaccines: 1. polyvalent vaccine produced in Belarus; 2. experimental thiosulfate vaccine in which there was used 30% sodium solution; 3. experimental emulsified vaccine; experimental emulsified + sodium + thiosulfate vaccine.

In the conditions of immunization of swine by experimental produced at Vitebsk Biofactory in the Republic of Belarus vaccines in blood of experimental swine there stated the morphological changes which pointed to formation of immune response.

After immunization of 30-35 day old piglets against a salmonellosis, pasteurellosis and streptococcosis (SPS) with special produced in the Republic of Belarus SPS vaccine in combination with immunostimulant sodium thyosulfate and vitamin C there was observed an activation myeloblastic hemopoiesis and lowering of erythropoeisis.

Analysis of morphological characteristic and parameters of a thyroid gland of a thyroid gland of growing cattle stock made it possible to specificate the age-specific and species-specific parameters of adaptation of cattle in concrete conditions of environment was realized in the conditions of cattle breeding complexes of the Republic of Belarus. As a result of studies there were obtained new data on form-building processes, macromorphology, topography and referential parameters of thyroid gland of cattle breeds.