1. Genetic aspects of male fertility in cattle;Koger,1980
2. Sterility in bulls;Lagerlőf;Vet. Rec.,1936
3. The systematic examination of bulls on the grounds of fertility and recording of the results in the pedigree herdbooks;Sluis,1961
4. Breeding soundness in bulls — a summary of 10,940 examinations;Carroll;J. Am. Vet. Med. Assoc.,1963