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I saw a referral case from a local veterinarian: a four-year-old Labrador bitch that was reported to have undergone routine spaying at 8 months of age. Over an extended period, the owner noted intermittent episodes of vulvar discharge, which could be described as mucoid to mildly blood-tinged. These episodes were not associated with overt illness. The bitch remained bright, active, and in good body condition, with no reported behavioural signs suggestive of oestrus. There was no history of marked vulvar swelling, attraction of male dogs or any systemic illness. 

General physical examination was unremarkable: normal temperature, pulse, and respiration, good body condition and no abdominal discomfort. The only consistent abnormality was intermittent vulvar discharge, observed clinically and confirmed on history.

Vaginoscopy revealed pink vaginal mucosa, relatively small, rounded mucosal folds and evidence of epithelial exfoliation. At face value, this appearance could be interpreted as consistent with dioestrus. However, the findings lacked the classical features of a fully progesterone-dominated state. Cytological examination showed a thick smear, with a predominance of intermediate epithelial cells and the presence of neutrophils and bacteria: in short, these findings appeared to be typical of early dioestrus. However, serum progesterone concentration was 1.7 nmol/L (basal). This is important because in the normal cycling bitch, even early dioestrus is characterised by a measurable rise in progesterone. A basal value effectively excludes recent ovulation and significant luteinisation.

Given the persistent discharge and equivocal diagnostic findings, exploratory surgery was performed. Residual ovarian tissue was found on both remaining ovarian pedicles. Each remnant contained a single, thin-walled follicle, without obvious gross evidence of luteinisation. A large uterine remnant was found, which in the previous surgery had been transected midway along the length of each uterine horn. The uterine remnant was adhered to the jejunum.  

These findings were interesting because there appeared to be a mismatch between vaginoscopic and vaginal cytology findings, and progesterone concentration which was confirmed by gross ovarian morphology (a single ovarian follicle on each ovary, with no luteinisation)

Rather than forcing these findings into the framework of a normal oestrous cycle, I would speculate that this bitch was not truly cycling at all.

In the normal bitch, multiple follicles develop under FSH stimulation, and produce sufficient oestradiol to induce pro-oestrus and trigger the LH surge result in ovulation and complete luteinisation. In this case, however, only two follicles were present and total granulosa cell mass was therefore markedly reduced.

Could the follicles have produced enough oestradiol to influence the vaginal epithelium, but not enough to trigger ovulation or luteinisation, resulting in a state of chronic, subthreshold oestrogenisation? In this case, the retained uterine tissue effectively acted as a clinical signal of hormonal state, generating a mucohaemorrhagic discharge which revealed the presence of hormonally active ovarian tissue.

 

One might reasonably speculate that many bitches with small ovarian remnants may go undetected, since where little or no uterine tissue remains, there may be no discharge, and without behavioural signs or clinical abnormalities, such animals could exist in a similar endocrine “limbo,” without ever coming to clinical attention.

An important clinical consideration is whether such cases carry a risk of pyometra. Classical pyometra depends on sustained progesterone dominance, but in this patient, progesterone remained basal, suggesting that the risk of typical pyometra is likely low. However, chronic low-grade endometrial stimulation and intermittent inflammation may still produce ongoing discharge or milder uterine pathology.

This case highlights an important variation of ovarian remnant syndrome: Not all cases need present with overt oestrus, and not all hormonally active remnants produce a luteal phase. Some patients may exist in a subclinical, hormonally incomplete state. In such cases, vaginal cytology and vaginoscopy may be misleading, progesterone measurement remains critical and, as always, definitive diagnosis will likely require surgical exploration.