Factors affecting the relative fertility of males determined by heterospermic insemination in vivo and in vitro

Insemination of females with mixed sperm from two or more males often results in a disproportionate number of offspring sired by each of the males. Why one male is relatively more fertile than another male as demonstrated by insemination of mixed sperm is not known. Fluorochrome labels were used to identify sperm from various strains of mice and these sperm were mixed and added to either zona pellucida-intact or zona free eggs in vitro or inseminated in vivo. Competing sperm from ICR and B6D2F1 males demonstrated that ICR males had a greater proportion of fertilizing sperm in vitro than did B6D2F1 males and was not affected by removing the egg vestments. The percentage of in vitro fertilizing ICR sperm, however, was greater than the proportion of fertilizing ICR sperm determined in vivo or the proportion of fetuses sired by each of the males. Competing sperm from ICR and C57BL/6N males demonstrated that ICR males had a greater proportion of fertilizing sperm in vitro and in vivo and was reduced in vitro by removing the cumulus and zona pellucida. Competing sperm preincubated for either 0 or 2 h under capacitating conditions could alter the percentage of fertilizing sperm from each of the three strains. The rate of fertilization was examined between 2 and 30 h after (homospermic) insemination with sperm from either ICR or B6D2Fl males in vitro or in vivo. No differences were observed between the two males. In addition, time of insemination relative to ovulation using ICR and C57BL/6N males tended to affect the proportion of offspring sired by each of the males.In conclusion the efficiency at which sperm from various males can penetrate the cumulus and zona pellucida may affect their relative fertility. The rate of sperm capacitation may influence their ability to penetrate these vestments. Other factors such as sperm survival and acrosomal enzyme content need to be investigated.U of I OnlyETDs are only available to UIUC Users without author permissio