Investigation of stress reaction response and productivity of poultry by means of stimulation of natural resistance by biologically active substances was realized in the conditions of the Republic of Belarus by an example of 4 experimental group of broiler chickens of Kobb-500 cross. The first group was a control one. Chickens of the second group were administrated preparation Vigozin twofold in dose of 1 ml/l with water in course of the first three days in 2 cycles and with interval of 8 days. Chickens of the third group were given the preparation with water in dose of 1 ml/1 in course of the first 3 days. The fourth group was given the preparation with water in dose of 1 ml/1 in course of the first 5 days. In course of observation over chickens there was analyzed their clinical state, mortality rate, weight gain, and meat yield. In course of study in chickens of experimental group the daily average weight gain was 37,8 g against 34,1 in control; average live weight – 1099,6 +/- 7,57 g against 95,98 +/- 0,50 g in control. In 46-day old broiler chickens the average daily weight gain was 46,2 g against 43,1 g in control, average live weight – 2166,94 +/- 0,49 g against 2021,08 +/- 1,05 g in control. Forage expenses per 1 kg of weight gain were 2,01 kg against 2,18 kg in control. Forage conversion was 7,8%. Research results proved the efficiency of application of Vigozin preparation: viability of chickens in the second group on increased 3,5%; the third group - on 1,7% ; in the fourth group - on 2,5%

Investigation of influence of probiotic Dialact and immunostimulant Alveozan on digesting of nutritive substances by broiler chickens of Kobb-500 cross, as well as control over their individual development were realized in the conditions of the Republic of Belarus. The first (control) group of chicken was given standard well-balanced ration. Chickens of the second group were administrated immunostimulant Alveozan in dose of 10 mkg/kg of live weight with drinking water once a day in course of 5 days, with 10 days interval till the end of the growing period. Chickens of the third group were administrated preparation Dialact in dose of 0,1-0,2 ml with drinking water once a day in course of 3 days, with 14 days interval till the end of growing period. Chickens of the fourth group were given Alveozan in dose of 10 microgram/kg of live weight once a day in course of 5 days with 10 days interval, and Dialact in dose 0,1-0,2 ml once a day in course of 3 days, with 6 and 14 days interval. Research results showed that complex application of probiotic Dialact and immunostimulant Alveozan increased the viability of chickens on 100%, average live weight - on 5,1%, average daily weight gain - on 5,1%. Administration of Dialact and Alveozan, both separately and in complex, increased the digestibility of nutritive substances of mixed fodders: application of nitrogen increased on 1,93-6,38%, application of calcium decreased on 10,41-12,54%, phosphorus use increased on 2,38%

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

Influence of potassium orotate on hematological, immunomorphological indexes and and marrowy myelopoiesis of broiler chickens in the process of oral associated immunization against infectious bronchitis and poultry Newcastle disease was investigated in the conditions of the Republic of Belarus. There were studied 60 broiler chickens divided into 3 groups: one control group and two experimental ones. Research results established that potassium orotate application in combination with associated poultry immunization against infectious bronchitis and Newcastle disease increased the number of leucocytes and the volume of adenoid tissue as well as raised the lymphocytes density in thymus and bursa of Fabricius. In the bone marrow aspirates in 7 days after immunization in the control group there was stated the increasing of basophilic myelocytes number in comparison with the second experimental group. In 14 days in the control group there was noted the increasing of a total number of basophiles. In 21 days after immunization there were stated no considerable changes in the composition of basophil cells in the experimental groups. Research results showed that potassium orotate intensively stimulated the development of plasmocytic reaction in the conditions of multipartial immunization

In the conditions of the Republic of Belarus there was realized a morphological study of bone marrow aspirates at different terms chicken of immunization against Gumboro disease which made it possible to analyze the state of immune system for the objective evaluation of immunological status. Research results showed that chicken immunization with a national liquid chick embryo viral vaccine produced on the basis of KMIehV-13 strain against Gumboro disease (infectious bursal disease) promoted the development of immunomorphological remodeling of bone marrow. Application of immunostimulants Alveozan and Nukleovit for poultry vaccination caused more expressed changes revealing in statistically reliable increasing of total number of myeloblastic cells in the majority of cases by means of increasing of immature cells, and then mature cells of granulocytic series, as well as quantity of lymphocytes and plasmacytes