INTENSITY OF H-3 ACTINOMYCIN-D (H-3-AMD) BINDING TO CHROMATIN OF BULLSPERMATOZOA

Three groups of bulls (age 25 months; 6 bulls in each group) were used for 12 months with varying ejaculation frequency (four, six and eight ejaculates weekly in the respective groups). The ejaculates were subj ected to cryopreservation. Despite statistically significant differenc es regarding the number of spermatozoa produced per week (27.2 x 10(9) -46.5 x 10(9) sperm per week) no effect of the high ejaculation freque ncy upon the indices of semen quality was observed, both before and af ter freezing-thawing. Nevertheless, spermatozoa obtained from the bull s used with the highest frequency (eight ejaculates per week) showed s ome disturbance in chromatin condensation after freezing-thawing. This phenomenon was expressed by an inhibition of the incorporation of tri tiated actinomycin (H-3-AMD) into the nuclei of spermatozoa incubated for 30 min and 60 min in the presence of H-3-AMD. This suggests altera tion of sperm nuclear chromatin due to an 'overcondensation' state aft er freezing-thawing of bull semen when the individual limit of sperm o utput per week is exceeded. This phenomenon may cause a lower concepti on rate after cryopreservation.