1. Institute of Animal Reproduction and Food Research of Polish Academy of Sciences, Olsztyn, Poland
2. Institute of Veterinary Medicine, Nicolaus Copernicus University, Torun, Poland
3. Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Department of Animal Reproduction, Madrid, Spain
4. Telomeres and Telomerase Group, Spanish National Cancer Research Centre (CNIO), Madrid, Spain