Question

How many eggs do you think were released by the ovary of a female dog that gave birth to 6 puppies?

Answer 1

Hint Dogs are polyovulatory animals. Poly Ovulation is the production of more than one ova from the ovary. It is a type of adaptation for ensuring an adequate supply of zygotes for maximum litter production.

Complete answer:
The number of eggs released mainly depends on the size and age, breed, and health of the dog. Whereas, the number of those fertilized depends on the timing of breeding and the viability of the sperm.
In female dogs, puberty or sexual maturity usually occurs around 9 to 10 months of age. The smaller and dwarf breeds tend to go into the estrus stage or 'heat' earlier and also some females can have their first heat cycle as early as four months of age. On the other hand, it is observed that the large and giant breeds can be up to two years old or more before they come into heat. Additionally, dogs are poly-ovulatory animals which mean that more than one ova is produced from the ovary.
So, according to the question if the dog gave birth to 6 puppies then 6 eggs must have been released from the ovary at the same time. These eggs would have undergone successful fertilization and implantation. Therefore six zygotes are formed, each of which develops into a puppy.

Additional information:
The four stages of the female dog’s reproductive cycle include:
-Proestrus
Proestrus lasts for about nine days and is the first stage of the reproductive cycle. The signs of proestrus are:
Swelling of the vulva
Bloody discharge
-Estrus
The signs of estrus are:
A soft and enlarged vulva
Discharge lightens in color and decreases
-Diestrus
Diestrus is the final stage of the cycle. It typically occurs around day 14 and all signs of swelling and discharge are gone.
-Anestrus
Anestrus is the stage between diestrus and the next proestrus. This stage lasts for about 4 months and in certain breeds, it can be much longer. There is no swelling in the vulva and no vaginal discharge. The body uses this specific period to allow the uterus to prepare for the next possible pregnancy.
Notes: In both mono-ovulatory species, for example cattle and humans, and poly-ovulatory species, for example pigs and dogs, the interactions among extra-ovarian gonadotropins, metabolic hormones, and intra-ovarian growth factors determine the development of follicles and the number of follicles that ovulate. Antral follicle growth is regulated by hormones such as FSH and LH in both mono- and poly-ovular species.