1. Department of Cryobiology, Institute of Biology and Immunology of Reproduction, Bulgarian Academy of Sciences, Sofia, Bulgaria
2. Department of Immunoneuroendocrinology, Institute of Biology and Immunology of Reproduction, Bulgarian Academy of Sciences, Sofia, Bulgaria
3. Department of Animal Reproduction and Artificial Insemination, Veterinary Research Division, National Research Centre (NRC), Cairo, Egypt
4. Department of Embryobiotechnology, Institute of Biology and Immunology of Reproduction, Bulgarian Academy of Sciences, Sofia, Bulgaria