1. Graf Lehndorff Institute for Equine Science; Neustadt (Dosse) 16845 Germany
2. Centre for Artificial Insemination and Embryo Transfer; University of Veterinary Sciences; Vienna 1210 Austria
3. Division of Biochemistry; University of Veterinary Sciences; Vienna 1210 Austria
4. Section for Obstetrics and Reproduction; University of Veterinary Sciences; Vienna 1210 Austria