Shortened interestrous intervals occur most commonly with premature luteolysis about one month after ovulation in the bitch. If premature luteolysis occurs
following fertile breeding, progestational support will need to be provided for pregnancy maintenance (see Table 1). In some
species, premature luteolysis has been linked to abnormalities of ovulation, suggesting that ovulation induction at a later
estrus may be indicated.
Persistent estrus is confirmed estrus (receptivity to mating with vaginal cornification) for more than 21 days in the bitch or more than 19
days in the queen. Causes of persistent estrus in the bitch and queen include follicular cysts of the ovary or functional
granulosa cell tumors, both of which are detectable on ultrasound or surgical exploration of the abdomen. Some, but not all,
follicular cysts of the ovary respond to medical attempts at ovulation induction.
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