Normal Hormonal Cycle in Female Dogs
In female dogs, biannually, during the nine days of pro oestrus, the pituitary gland at the base of the brain produces a follicle stimulating hormone which triggers the oestrogen production and causes eggs that are stored in the ovaries to mature. When these are released at ovulation which commences around day nine of pro oestrus, and continues for up to for five days, the vacated sites produce progesterone, which is the hormonal requirement of pregnancy. The production of eggs at oestrus acts as a stimulus for the bitch to accept a dog for mating but this activity occurs in the body whether or not a mating has taken place. The met oestrus in the biannual cycle prepares her for the tasks of nurturing the fertilised eggs and then the growing foetus, the whelping, and the milk production required once the puppies are born.
If no mating has taken place, then progesterone production gradually ceases so that by the twentieth day of met oestrus the hormone levels are returning to normal and by the commencement of an oestrus, which is the resting period, all reproductive and sexual activity has stopped for a further seventy to seventy-five days when pro oestrus recommences.
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