Canine Pseudopregnancy: A Review

This chapter reviews the most relevant features of the patho-physiology, clinical signs, diagnosis, treatment and prevention of overt, i.e. clinical, pseudopregnancy in dogs. Clinical pseudopregnancy is a syndrome observed in non-pregnant dogs and is characterized by clinical signs such as nesting, weight gain, mammary enlargement and lactation. It typically occurs in nonpregnant bitches about 6 to 12 weeks after estrus. Diagnosis is based on clinical signs. While prolactin has a central role in the symptomology of clinical pseudopregnancy, the precise etiology is not yet completely understood. Some studies suggest that at some point during diestrus (metestrus) the circulating prolactin concentrations rise to higher than normal levels in overtly pseudopregnant bitches compared to those in unaffected bitches in diestrus. It is also possible that individual differences in peripheral sensitivity to prolactin, or even the existence of molecular variants of canine prolactin with different bioactivities, are involved in the variation of the incidence and severity of pseudopregnancy within and among breeds. Exposure to progesterone and subsequent withdrawal of progesterone is apparently involved, based on effects of exogenous progesterone and on the frequent induction of pseudopregnancy by spaying (ovariectomy or ovariohysterectomy) during the luteal phase, i.e., in the metestrus (diestrus) stage of the cycle. Considering that overt pseudopregnancy is usually a selflimiting and possibly a quasi-physiological state, mild cases usually are not presented for treatment or are determined to need no treatment. However, physical as well as behavioral changes can be so extensive as to be intolerable for owners, and treatment is typically sought late in the course of the syndrome. The reported relation between a history of overt pseudopregnancy and subsequent mammary tumor development suggests that treatment may be more important than previously assumed. Sex steroids and in particular progestins traditionally used to treat pseudopregnancy have side effects which outweigh any benefits, although androgens like mibolerone may be useful where available. Inhibition of prolactin release by administration of an ergot derivative such as bromocriptine, cabergoline or metergoline has proven to be highly effective for the treatment of canine pseudopregnancy, and more appropriate than the use of steroids. Although some of these ergot derivatives can present some untoward side effects, such effects are typically transient and can usually be tolerated or managed. Predisposed bitches not intended for breeding should be spayed because ovariectomy is the only permanent preventive measure.