In-vitro fertilization in the mouse and the relevance of different sperm/egg concentrations and volumes

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Abstract
The sperm-egg ratio and sperm concentration were varied separately by using different volumes (1-100 .mu.l) and egg numbers (1-15). The percent fertilization was determined by sperm concentration in large volumes (10-100 .mu.l). In small volumes (1 or 5 .mu.l) the number of spermatozoa/egg determined penetration rate; the effective epididymal sperm number/fertilization was 250-350. Spermatozoa obtained from the oviducts (i.e., naturally selected) gave good fertilization responses and low concentrations of epididymal spermatozoa were also more effective when oviductal fluid and cumulus cells were included in the inseminating volume. Sperm-egg collision rate is the most important factor determining percent fertilization, although heterogeneity of epididymal spermatozoa limits fertilization rate at low sperm-egg ratios.