Abstract
The investigation was carried out on the ovulation rate, ovulation ratio, and transuterine migration of the fertilized ovum in the dog.
The number of ova shed was determined by counting the number of corpora lutea in the ovaries of 135 mongrel bitches 24 years of age weighing about 10 kg each and autopsied during a period from 1 to 70 days after ovulation.
The transuterine migration of the fertilized ovum was considered on the basis of the number of corpora lutea in both ovaries and that of fetuses in both uterine horns of 69 pregnant ones among the 135 bitches.
The results obtained are as follows.
1. Rate of ovulation (in 135 bitches).
The ovulation rate of the dog in each estrus was 6.0±1.7 ova on the average with a range from 2 to 12; that is, 2.9±1.4, ranging from 0 to 8, in the right ovary and 3.1±1.4, ranging from 0 to 6, in the left ovary.
No influence of the season on the ovulation rate could be found statistically.
In the ovulation ratio of the right to the left ovary, no significant difference was observed.
2. Transuterine migration of the fertilized ovum (in 69 pregnant bitches).
Two of the 69 pregnant bitches were discarded from the data, as it was conjectured that plural ova might have been ovulated from a single ovarian follicle. Monozygotic twins were observed in only one bitch.
The fertilization rate of all the experimental bitches was 88.8%.
The number of fetuses in both uterine horns was equal to that of corpora lutea in both ovaries in 39 bitches (58.2%). The number of fetuses was one smaller than that of corpora lutea in 17 bitches (25.4%), two in 5 bitches (7.5%), and three, four, and five in 2 bitches each (8.9%).
It was observed that the rate of transuterine migration of the fertilized ovum was 49.3% in 33 of 67 bitches; that is, almost half the bitches had one or two ova. The direction of migration of the fertilized ovum was from the side of the predominant ovary to the uterine horn on the opposite side in 30 of 33 bitches. The ovulation rate in both ovaries was the same as in the other 3 bitches. As the consequence of the migration, the distribution of fetuses showed a tendency to be epual in both uterine horns. More fetuses were found in the uterine horn on such side as having a smaller number of corpora lutea in 11 bitches (33.3%).
