Megestrol acetate (Ovaban) currently is the only contraceptive drug approved for use in dogs in the United States. Ovaban is a long-acting progesterone. It inhibits the estrous cycle by suppressing the pituitary output of FSH (see Hormonal Effects During Estrous). The drug is safe and effective when used according to the manufacturer’s recommendations. A veterinary exami- nation is advised to rule out diabetes, pyometra, pregnancy, and mammary gland tumors before starting the drug. If any of these are present, Ovaban should not be used. The first heat cycle in puppy bitches frequently is unreli- able. To ensure proper drug performance, do not use Ovaban until the second heat.
To bring a bitch out of heat, start the pill at the first signs of proestrus. It must be started within the first three days of the heat cycle to prevent estrus and possible pregnancy. Ovaban is given for eight days. The next heat cycle will occur in two to nine months.
It is essential to adhere to a strict schedule with any contraceptive drug. Always confine your bitch during the first eight days of heat, since you might have missed the first signs of proestrus and started the drug too late. If an unplanned mating does take place and the bitch has not been on Ovaban for three full days, stop the pill and consult your veterinarian (see Unwanted Pregnancy). If mating occurs after the bitch has been on the pill for more than three days, complete the course. She will not become pregnant.
To postpone heat for a hunting trip, pleasure trip, or dog show, start the pill at least one week before leaving and continue it for 32 days. Ovaban must be started at least one week before proestrus to postpone a heat.
Bitches taking Ovaban may become hungry or lazy, gain weight, experience personality changes, or show mammary gland enlargement. These changes disappear when the drug is stopped. Because of the risk of pyometra associated with the prolonged use of progesterone, Ovaban should not be used to postpone heat or to take a bitch out of heat for more than two consecutive heat cycles.