FACTORS THAT INFLUENCE THE PROPORTION OF OFFSPRING SIRED BY A MALE FOLLOWING HETEROSPERMIC INSEMINATION

Heterospermic insemination (HI) is the situation when sperm from two o r more males are present in the female before fertilization, There are various means of distinguishing paternity after HI, extending from id entifying the fertilizing sperm microscopically to examining the pheno type of offspring, Invariably, sperm from one male fertilizes a majori ty of the eggs, The advantage one male may have can be due to an innat e difference between the males, an unequal ratio of sperm in the mixtu re or a more appropriate interval from insemination to ovulation when inseminations are not simultaneous. The relationship between the propo rtion of females that conceive from a homospermic insemination by a pa rticular male and the proportion of eggs fertilized after HI by that m ale is positive. The ranking of quality of semen by morphological, mot ility or biochemical tests corresponds in nearly every case with the r anking resulting from an index derived from HI. The effect of treatmen t of the male on his fertility can be detected readily by a change in the proportion of offspring he sires from HI. Sperm suspended in a les s than ideal extender, exposed to less than ideal handling procedures or stored for a prolonged period, will fertilize a smaller proportion of offspring when competing with sperm exposed to more suitable condit ions. The advantage a sperm may have in HI may be associated with the speed of attachment to and penetration of the egg. HI provides a means of more accurate assessment of the relative fertilizing ability of sp erm with fewer observations than with most other techniques.