The estrous cycles of bitches and queens are not as easily manipulated as in other species. Most protocols are not based on controlled studies, so manipulation of the first estrous cycle in valuable breeding individuals is not advised. Although onset of a particular cycle may be delayed, return to normal cycling is highly variable.
Induction of estrus in bitches is possible in late anestrus by using prolactin inhibitors (eg, bromocriptine, cabergoline). Cabergoline is preferred over bromocriptine because fewer GI adverse effects occur.
Ovariohysterectomy or ovariectomy is the best method to prevent the estrous cycle in bitches and queens. Gonad-sparing neutering requires prevention of unintended breedings, as hormone stimulation in animals with intact gonads will still induce these animals to mate.
Long-term suppression of estrous cycles by using androgens is not advised because it is not documented to be safe in breeding bitches, although many anecdotal opinions exist. Common adverse effects are breakthrough proestrus, clitoral hypertrophy, vaginitis (especially in prepubertal females), increased activity of skin sebaceous glands, mild epiphora, and alterations in hepatic function studies.
After treatment is discontinued, return to estrus is approximately 70–90 days but can be variable.
Conception rates are reportedly normal by the second cycle after treatment. If given to pregnant dogs, synthetic androgens induce severe developmental anomalies in the urogenital system of female puppies. The safety and efficacy of injectable testosterone, which is commonly administered to racing Greyhounds, has not been supported by controlled studies and is not advised. Androgens should not be given to queens.
The use of megestrol acetate, a synthetic progestagen, is not advised in breeding females because of the increased risk of cystic endometrial hyperplasia and pyometra, as well as other adverse effects (eg, mammary hyperplasia and neoplasia, hyperglycemia secondary to insulin resistance, and rebound hyperprolactinemia and lactation).
Suppression via downregulation (and induction) of estrous cycles by the use of synthetic GnRH implants has been described in bitches; it can be successful, but the products are not universally available. Estrus induction in bitches can be accomplished with prolactin inhibitors (cabergoline 2.5–5 mcg/kg, PO, every 24 hours); anestrus of at least 2 months duration must precede induction to permit uterine involution and repair. The product is discontinued after proestrus is present (usually day 2–8), thus downregulation does not occur.
Ovulation can be induced in estrual queens physically or, more reliably, hormonally to produce a luteal phase (diestrus or metestrus) of approximately 45 days. Physical methods include breeding with a vasectomized tom (very effective) or inserting a sterile swab or glass rod into the vagina. The latter should be performed repeatedly for best results. Hormonal methods include administration of human chorionic gonadotropin (500 IU/queen, IM, every 24 hours for 2 days) or GnRH (25 mcg/queen, IM, every 24 hours for 2 days).
