Biology of Reproduction, Vol 24, 637-642, Copyright © 1981 by Society for the Study of Reproduction

Fertilization in vitro of Rabbit Eggs by Epididymal Spermatozoa Capacitated in a Chemically Defined Medium

¹ Department of Animal Science, College of Agriculture, Kyoto University, Kyoto 606, Japan

Newly ovulated eggs from mature does treated with FSH and hCG were inseminated in a defined medium with epididymal spermatozoa which were treated with the standard or HIS medium for 15 mm and preincubated for 10-10.5 h in a CO₂ incubator. When spermatozoa in which viability after preincubation was maintained at levels of 50-60% were used, sperm penetration through the zona pellucida started 1-1.25 h after insemination and the transformation of sperm head into the male pronucleus occurred within 2 h in spermatozoa treated either with the standard or with HIS media. There was no significant difference between the overall penetration rates of the eggs 1-5.25 h after insemination with the spermatozoa treated with the standard (68.3%) or HIS media (59.1%). Most of the penetrated eggs developed to 2- or 4-cell and 8-16-cell stages 24 and 48 h after insemination, respectively. When four denuded eggs were inseminated with spermatozoa preincubared after treatment with the standard medium, all of them were penetrated with male pronucleus 5 h later. In some bucks, the proportion of motile spermatozoa after preincubation was greatly decreased (less than 5%), and such spermatozoa showed very low penetration ability.

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ACKNOWLEDGMENTS A portion of this work was supported by a grant from the Ford Foundation (No. 740-0404).