Evaluation by the heterospermic insemination technique of the differential effect of freezing at -196°C on fertility of individual bull semen

Abstract

A.R.C. Unit of Animal Genetics, Department of Genetics, West Mains Road, Edinburgh EH9 3JN, Ministry of Agriculture, Fisheries and Food, Cattle Breeding Centre, Shinfield, Reading RG2 9BZ, A.R.C. Cattle Blood-Typing Service, Animal Breeding Research Organization, West Mains Road, Edinburgh EH93JQ, and§Department of Anatomy, Royal Veterinary College, London NW1OTU, U.K. This paper gives evidence that deep freezing depresses the fertility of the semen of different bulls unequally, that the period of time spent in the frozen state has no additional effect, and that replicate experiments with mixed (heterospermic) insemination give concordant results. The paper marks a further stage in an experiment with heterospermic insemination replicated over 6 successive weeks in December 1969-January 1970. In each replicate one semen mixture was made containing equal numbers of spermatozoa newly collected from the same four bulls. Some of each mixture was inseminated unfrozen (fresh semen) and another part after standard freezing at −196°C in