Spontaneous sister chromatid exchanges in mitotic chromosomes of cattle (Bos taurus L.) [lymphocyte culture]

Peripheral blood lymphocytes from 4 cattle donors were grown for 2 cell cycles in the presence of 0.1, 0.25, 0.5, 1.0, 2.5 and 5.0 mu g/ml of 5-bromodeoxyuridine in order to detect the spontaneous level of sister chromatid exchanges and the dose-response relationships at low bromodeoxyuridine levels. Sister chromatid exchanges were counted on 50 s cycle metaphase spreads, randomly scored, for each donor at each dose. The mean rate of sister chromatid exchanges/cell at 0.1 mu g/ml of BUdR was 2.48 plus or minus 1.75, which can be considered as spontaneous. The dose-response curve increased more rapidly from 0.1 to 0.5 mu g/ml of bromodeoxyuridine and less rapidly at higher concentrations. The frequency distribution of sister chromatid exchanges/cell and that of chromosomes showing various numbers of exchanges followed the Poisson probability function only within the range of 0.1 to 1.0 mu g/ml of bromodeoxyuridine. The usefulness of determining the spontaneous level of sister chromatid exchanges in domestic animals is discussed in relation to its possible application for selection programs.