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BITCHES are monoestrous, with long luteal phases and several months of anoestrus between active reproductive phases. Luteal function is almost identical in pregnant and non-pregnant females (Inaba and others 1998). If a bitch is not allowed to breed, or is not pregnant after mating, dog owners must wait several months before the termination of dioestrus and anoestrus, and reappearance of another follicular phase during which mating and pregnancy can occur. A reliable method for promoting luteal regression and inducing ovulation would aid the clinical management of prolonged anoestrus or infertility in valuable breeding dogs. Prostaglandin F2α (PGF2α) is believed to have luteolytic properties in bitches. Although treatment for four days with PGF2α in the early or mid-luteal phase terminates pregnancy without clinically apparent resorption of embryos (Romagnoli and others 1993), it is difficult to predict the onset of subsequent oestrus in bitches treated with prostaglandin. Attempts to induce fertile oestrus in anoestrous dogs using a depot-injectable form of the potent gonadotrophin-releasing hormone (GnRH) agonist leuprolide acetate have been successful (Inaba and others 1998). It has been reported that histological changes similar to involution in the bitch's endometrium are not complete until 135 days after the most recent oestrus, regardless of whether or not the bitch was pregnant, and that induction of oestrus before this time may result in reduced fertility (Kutzler 2007).
This short communication describes a study to …