1. Agricultural Academy, 30 Suhodolska Str., 1373 Sofia, Bulgaria
2. Department of Agrobiotechnology, AgroBioInstitute, Agricultural Academy, 8 Dragan Tsankov Blvd., 1164 Sofia, Bulgaria
3. Department of Livestock Sciences, Agricultural University (AU), 12 Mendeleev Blvd., 4000 Plovdiv, Bulgaria