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%

Analysis of the optimal scheme of doses and rates of combined administration of probiotic Dialakt and immunostimulant Alveozan was realized in the conditions of the Republic of Belarus by the example of 1500 broiler chickens of cross Kobb- 500. Chickens of the first (controlled) group were given only total ration, balanced with the main nutrients. For the chickens of the second group were administrated with immunostimulant Alveozan with water starting from one day old age, every day in dose of 10 mkg/kg of body weight once a day in course of 5 days successively and with 7 days interval till the end of growing period; and probiotic Dialakt was administrated with water in dose of 0,1-0,2 ml/head (10,0-20,0 mln microbial bodies) starting from one day old age, once a day in course of 5 days successively and with 6 and 14 days intervals till the end of growing period. Chickens of the third group were administrated Alveozan in dose of 10 mkg/kg of body weight with drinking water once a day in course of 5 days with 10 days interval till the end of growing period; and Dialakt in dose of 0,1-0,2 ml/head with drinking water starting from one day old age, every day in course of 5 days with 6 and 14 days interval till the end of growing period. The research results showed the following optimal regime of complex application of the analyzed preparations: immunostimulant Dialakt - in dose of 0,1-0,2 ml/head with drinking water starting from one day old age, once a day in course of 3 days successively with 6 and 14 days intervals till the end of growing period; and immunostimulant Alveozan - in doze of 10 mkg/kg of body weight with drinking water once a day in course of 5 days with 10 days interval till the end of growing period. Complex application of Dialakt and Alveozan promoted the increasing of organometric indexes, specific volume and size of thymus in 1,5-1,8 times (P less than 0,01), Fabritsiya bursa - in 2 times (P less than 0,01) and lien - on 11,1% (P less than 0,05)

In course of realized in the conditions of the Republic of Belarus evaluation of growing intensity and level of meat productivity depending on cattle sex there was conducted the scientific and economic experiment by an example of two groups of white-and-black bull-calves and heifer calves. In the first growing period the animals of experimental groups were fed with milk substitute. At the stage of completion of growing and fattening the bulls and heifers of experimental groups obtained ration containing haylage, plus 2 kg of flattened grains and 2 kg mixed fodders. Results of linear and weight indexes analysis showed that in changes of exterior of bulls and heifers of black-and-white breed there was noted a certain regularities in their growth and development. The most intensive growth and development of analyzed young cattle was stated at age from 6 till 12 months. At the same time, bulls exceeded heifers according to the main exterior indexes. According to the visual evaluation of bulls and heifers there were determined the differences in constitutional type