When mixtures of semen containing an equal number of spermatozoa from two males are inseminated, the males usually sire disproportionate numbers of the offspring. In this study, when a mixture of equal numbers of spermatozoa from a Columbian (C) and a Leghorn (L1) cock was inseminated, the C male sired 34% of the offspring. The proportion of offspring was constant regardless of age of males, season, total number of spermatozoa, breed of hen or the interval from insemination to the time of egg-lay over a 15-day period after insemination. The proportion of C offspring observed from inseminating nine different ratios of spermatozoa arranged progressively from 1C :9L, 2C:8L and so on, was 10%, 20%, 23%, 34%, 38%, 44%, 58%, 74% and 82%. These results were in close agreement with mathematically derived estimates. It appears that the relationship between sperm ratios and the proportions of offspring sired by two males competing heterospermically is dependent on the ratio of the number of competing spermatozoa but not on total number, season, breed of hen or the interval from insemination to fertilization.
Chance is ordinarily considered to be responsible for determining which spermatozoon fertilizes an egg. Results from experiments on competitive fertilization in hens tend to disprove this concept. When fresh and aged cock spermatozoa competed directly, the eggs were fertilized by the fresh spermatozoa, although the aged spermatozoa alone were capable of fertilization (Warren & Kilpatrick, 1929
A study of varying combinations of in vitro-aged sperm and in vivo-aged ova at 3 hr intervals from 0-24 hr resulted in failures at different steps of the fertilization process during in vitro fertilization of mouse ova. Significant decreases caused by sperm aging, ova aging, and sperm X ova aging interaction were found in sperm penetration. Pronuclear formation was not affected by sperm aging and was enhanced by ova aging, and there was a significant effect of sperm X ova aging interaction. Sperm aging significantly influenced the prometaphase stage of the fertilization process. Therefore, it is suggested that the detrimental fertilization effects resulting from aging gametes are due to different mechanisms in sperm and ova, that these mechanisms are affected at different times, and that they affect different steps in the fertilization process.
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