In the conditions of the Republic of Belarus there was analyzed the influence of inclusion into broiler chickens diets of probiotoc preparation Bifidoflorin zhidkij (liquid) and prediotic veterinary drug Biofon AIL on the natural resistance, hematopoiesis, growth, metabolic function, development and viability of broiler chickens. In course of the study there was analyzed the dynamics of total haemoglobin, total protein of blood serum, albumins and globulins of broiler chickens which were fed with veterinary drugs probiotoc Bifidoflorin zhidkij and prediotic Biofon AIL. Indexes of chicken viability and life weight gain were marked. Research results showed that application of the presented veterinary preparations rendered the growth promoting action, lowering of disease incidence, increasing of chicken viability, increasing of live weight gain and stimulation of metabolic processes in the most intense period of poultry growing. All these factors were expressed in highest degree after the combined application of the probiotic and prebiotic veterinary drugs.

In the conditions of the Republic of Belarus there were analyzed the peculiar features of morphology of bursa of Fabricius of turkeys broad-breasted white turkeys at the stage of postnatal ontogenesis. Research results showed that postnatal ontogenesis of bursa of Fabricius of turkeys developed irregularly with preservation of organ up to 220 days. At turkeys in 300-day old age the organ preserved only in 45% of bird units. Form, colour and consistency of bursa of Fabricius depended on bird age. The absolute weight of the organ increased up to 220 days. The relative weight was maximum at 20-day old age. The sexual peculiar features of the organ morphology were insignificant; they revealed after the beginning of sexual maturity and expressed by some difference in weight and linear dimensions.

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%