Gamete physiology and timing of ovulation and fertilization in dogs.

Ovulation in most bitches occurs between 48-60 and 72 h from the onset of oestrus. The eggs are ovulated as primary oocytes and are not capable of being fertilized until about 60 h after ovulation when they undergo the first meiotic division to become secondary oocytes. By this time the ova have descended through two-thirds of the oviduct. Ova are fertilizable from the time of undergoing the first meiotic division at 60 h after ovulation until about 108 h after ovulation, i.e. for a period of about 48 h. The period during which the spermatozoa remain capable of fertilization in the female reproductive tract is thought to be about 5 days. The mating period during which conception is possible is thus about 7 days from the onset of oestrus.