Five Holstein-Friesian calves, from one sire, with prevalent black hair coat pigmentation were used in the experiment. The mean age was 33 days and the mean live weight 51 kg. The animals were exposed free running without interruption for 12 hours to an artificial ultraviolet light in the range of 280-320 nm. The mean dosis of radiation was 179. 10(-10) J/h/m. One-spot high-pressure mercury discharge lamps Tesla RVK 400 W were used as a radiation source. The dose rate was estimated from measurements by a spectral photometer with filter UG 2 for absorbtion of visible light located at the height of the back of standing calf. Blood samples were collected immediately before the beginning of treatment and after 5, 12, 24, 48 and 72 hours. The blood plasma aldosterone was measured by radioimmunoassays, the levels of sodium, potassium and calcium in blood plasma by flame spectrophotometry. Double classification variance analysis and evaluation according to the Snedecor F-test, the contrast effect test according to Duncan and regression analysis were used for statistical evaluation. Compared to the first sampling, sodium increased significantly after 5 and 12 hours of exposure (Tab. I) to 138.1 and 138.3 mmol/l, respectively. In the subsequent samplings this trend continued up to 72 hours from the beginning of irradiation (140.5 mmol/1). The potassium level did not change statistically significantly. Owing to an excessive irradiation, the calcium concentration increased significantly. The greatest oncrease occurred after 12 hours of irradiation (from 2.29 mmol/l to 2.61 mmol/l) and after 36 hours from the and of irradiation (2.70 mmol/l). The aldosterone level showed the greatest increase as early as after 5 hours of irradiation (from 8.54 ng/l to 17.22 ng/l) and 12 hours after the termination of exposure it returned to the initial level. The correlations between the irradiation doses during 5 and 12 hours of exposure and the single indices are given in Tab. II. In the case of sodium, the relations were always positive and weak, with the exception of the blood sampling after 72 hours (r = 0.726; r = 0.742). The potassium level was in negative correlation with the irradiation dose in most observations, medium strong dependence (r = -0.406; r = -0.387) having been recorded 12 hours after the termination of ultraviolet light action. In this sampling a medium strong relation was also found in the K:Na ratio to irradiation doses (r = 0.367; r = 0.350). The aldosterone concentration was in indirect relation to the irradiation doses, the closest coefficient was registered 12 hours after the termination of exposure (r = -0.510; r = -0.473). The dependence between calcium and irradiation doses was reduced as late as at the end of observation (r = 0.598; r = 0.638). The correlation coefficient between the aldosterone and sodium levels was highest before the beginning of irradiation (r = 0.665). Conversely, after 5 hours of ultraviolet light exposure it changed into r = -0.629 (Tab. III). In the subsequent observations, with the exception of the blood sampling 12 hours after the termination of the stress, the dependences were also negative. Aldosterone and potassium were in a slight indirectly proportional relation. Exceptions are the observation made in 12 and 36 hours after the end of the intervention (r = 0.704; r = 0.393) owing to the concentration decrease in the two indices. Sodium and potassium were in a medium strong negative relation before the exposure (r = -0.355). Owing to the increase in the values of the two indicators after 5 hours of stress, a positive close dependence at the level of significance (r = 0.863) was found. No visible erythema was discovered on the calves as a result of the 12 hours lasting irradiation only on the 3rd and 4th day there occurred burns on the muzzle of those animals which fell ill of keratitis attended by marked flow of tears. Two calves were discarded because of repeated health disorders.
