In the performed experiments the response of sympatho-adrenal and hypothalamo-pituitary-adrenal system was evaluated in sheep stressed by repeated isolation from the flock. Immature female sheep of the Polish Mountain breed were used. They were divided into control and experimental (isolated) groups, each of 10 animals. The sheep of the experimental group were isolated individually, three times for 180 min in 24h intervals. The blood was taken 30 minutes before, and 10, 30, 60 and 180 minutes after onset of isolation stress by means of cannula inserted into jugular vein. The activity of the sympatho-adrenal system was demonstrated by the plasma level of adrenaline (A) and noradrenaline (NA) and activity of the hypothalamo-pituitary-adrenal system by plasma level of cortisol. The concentration of catecholamines and cortisol were determined by the REA and RIA method, respectively. The highest concentration of the determined hormones was observed during the first isolation stress. The maximal level of catecholamines appeared at 10 min and cortisol between 30 and 60 min of stress. The patterns of increment in successive isolations were not altered, only the maximal levels of the hormones were reduced; the highest decline was noted in A level in lower NA and cortisol concentrations. These changes were determined by the calculated mean integrated responses; for A they were seven times and for NA and cortisol two times lower, compared to the first isolation. It is concluded that repeated isolation stress performed in similar time intervals leads to a systematic reduction of the response of sympatho-adrenal and hypothalamo-pituitary-adrenal system. This indicates a development of adaptation processes to the applied stressor.
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