The phenomenon of freemartinism continues to be a subject of research and interest to breeders due to economic losses resulting from sterility of females (of sheep and cattle) affected by leukocytic chimerism. In high fecundity sheep breeds such as Romanowska or Booroola this phenomenon occurs more frequently than in other breed populations. In Romanowska sheep it is connected with the cumulative effect of different genes, but in Booroola with the presence of gene F (high fecundity). Very little data is available in literature on freemartinism in the high fecundity Olkuska sheep which belongs to the breeds under threat of extinction. In view of high reproductive performance (early sexual maturity) and dairy production traits (high milk production) it seemed reasonable to undertake cytogenetic studies aimed at the determination of leukocytic chimerism related with freemartinism on a selected group of the Olkuska sheep. We examined a total of 40 animals of 13 chosen families with heterosexual litters. It was found that 2 out of 16 ewe-lambs were found to be freemartin cases (12.5%).
Cytogenetic studies were carried out involving 17 Polish merino ewes which were culled out as infertile because they remained barren in the course of two consecutive breeding seasons. Two among these females originated from twin pairs of different sex. Leukocytic chimerism 54,XX/54,XY characterized by the presence of two cell lines genetically differing by sex chromosomes was identified in one female. This ewe which was born in pair with a male possesed 41% of her male co-twin’s cells. During clinical examinations before slaughter a constriction of the vulva and vagina and enlargement of the clitoris were found. These changes would indicate the possibility of the incidence of similar deformations in structure of other parts of the genital tract. Gross examinations which were done, however, did not confirm these suppositions because the size and structure of the genital tract were identical to those in mature females. This leukocytic cell chimerism does not always manifest itself by an abnormality of female genital organs. This fact has been also confirmed by the results obtained by other authors.