Abstract
To determine the length of the viability of the unfertilized bitch ovum, 25 bitches were mated at varying intervals after ovulation. The time of ovulation was presumed from the grade of maturity of follicles observed by laparotomy 4860 hr after the onset of acceptance of the male.
All the animals were killed during 5.5 to 24 days after mating to examine oviducts and uterus for fertilized ova or embryos. The results obtained are as follows.
(1) The ovum remained fertilizable for 108 hr after ovulation; the earliest fertile mating occurred 54 hr preovulation and the latest fertile mating was found 120 hr after ovulation.
(2) Number of embryos per number of corpora lutea was the highest when mating were carried out from 12 to 120 hr after ovulation.
From these results, it is concluded that optimum period for fertile matings is from the 4th to the 7th day after the onset of acceptance of the male.
