PENETRATION OF MOUSE EGGS IN VITRO: OPTIMAL SPERM CONCENTRATION AND MINIMAL NUMBER OF SPERMATOZOA

Abstract

Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01545, U.S.A. (Received 21st December 1974) It is well known that a large number of the spermatozoa in the ejaculate reach the uterus but only a few are found in the oviducts of mammalian species after mating (see Bishop, 1961). This suggests that a small number of spermatozoa competent to fertilize may be selected during their passage through the female tract. In a study of the optimal sperm concentration and the minimal number of spermatozoa required to fertilize a rat egg in vitro, Niwa & Chang (1974a) have shown that the optimal sperm concentration was about 0·5 to 1·5 × 10⁶ spermatozoa/ml and that the minimal number of spermatozoa required to fertilize a rat egg was about 3000 to 6000 spermatozoa. The present experiment was designed to determine the optimal sperm concentration, the minimal number of spermatozoa required to fertilize a mouse