[Chromosome studies of 300 young Dutch-Friesian and Holstein-Friesian bulls intended for use in artificial insemination].

Three hundred young Dutch Friesian and Holstein-Friesian bulls, kept in the Central Opfokstation (Central Breeding Station) in Terwispel (Friesland), were studied cytogenetically, using conventional staining methods. Structural chromosome aberrations were not observed. Four animals showed XX/XY-chimerism in the lymphocytes, probably caused by the interchange of haemopoietic cells between the male and its female co-twin by placental vascular anastomosis. The number of (iso)chromatid gaps in 25 metaphase plates varied from 0 to 4. Chromosome breaks were not observed. The chimeric bulls and those with (iso)chromatid gaps were not found to show significantly reduced fertility rates.