Abstract
Animal cell chimerism denotes the presence of two or more cell lines of different genetic origin. The most common form of chimerism, which occurs spontaneously in mammals, is the presence of two or more cell populations in animals derived from dizygotic twin or multiple pregnancies. The aim of this review is to present extensive information on XX/XY chimerism in cattle, sheep and goats from the Bovidae family. Additionally, it will discuss a methodology for a quick and accurate diagnosis of cell chimerism and make an analysis of cells obtained from gonads of animals derived from twin pregnancies which underwent an exchange of hematopoietic tissue as a result of anastomoses. The studies reviewed here led the authors to conclude that XX/XY chimerism is generally undesirable in livestock breeding. Females (freemartins) are infertile, whereas in male carriers of chimerism, the impact of this abnormality on sperm parameters is still under discussion, therefore every case of different-sex twin or multiple births should be analyzed individually.