Spotaneous Rate of Sister Chromatid Exchanges (SCEs) in Mitotic Chromosomes of Sheep ( Ovis aries L.) and Comparison with Cattle ( Bos taurus L.), Goat ( Capra hircus L.) and River Buffalo ( Bubalus bubalis L.)

The spontaneous level of sister chromatid exchanges (SCEs) in the sheep, estimated by exposing peripheral blood lymphocytes in 0.1 μg/ml of 5′‐bromodeoxyuridine (BrdU), was 4.08 ± 2.47 SCE/cell, 2.04 SCE/cell cycle, 0.038 SCE/chromosome. The dose‐response relationships, observed by exposing the cells to 0.1, 0.25, 0.5, 1.0, 2.5, and 5.0 μg/ml of BrdU, rose rapidly from 0.1 to 0.25 μg/ml, and less rapidly at higher concentration s, thus reaching a saturation level. The analysis of variance, performed on the square root transformed data at 0.1 and 5 μg/ml of BrdU, indicated significant differences (P < 0.001) among the four donors tested. The distribution of the SCE/cell frequencies in the cell population of the four do ors followed the Poisson ‘mixture’ probability function, thus confirming previous findings. The spontaneous rate of SCE/cell of sheep is compared with those previously reported for cattle, goat and river buffalo. The theoretical and practical implications of the spontaneous sister chromatid exchanges are discussed in relation to their possible use in animal production for (a) better genetic evaluation of the breeding animals under selection, (b) more precise monitoring of the genotoxic effects of environmental pollutants.