It has been proposed that the pathophysiology of pseudopregnancy in spayed bitches is an unintentional consequence of ovariectomy or ovariohysterectomy during metoestrus/dioestrus (Gobello, 2021; Harvey et al., 1997, 1999; Root et al., 2018) instead of during anoestrus (the optimum time for spaying).
Diagnosis of pseudopregnancy in spayed bitches relies purely on history and clinical signs. Hormonal assays are non-diagnostic for persistent pseudopregnancy in spayed bitches, just as they are for overt pseudopregnancies in entire bitches.
Unfortunately, the bad news is that these pseudopregnancies may not resolve without intervention. Instead, they may become what is known as “persistent pseudopregnancy” (Harvey et al., 1999), which is also known as “chronic pseudopregnancy”, “chronic false pregnancy” or “chronic pseudocyesis”.
How does pseudopregnancy present in spayed bitches?
In the author’s experience, pseudopregnancy presents in two ways:
- Within days of spaying, with physical and/or behavioural signs of overt pseudopregnancy (Harvey et al., 1999)
- Within a few months of spaying, showing aggression and/or anxiety with or without any of the other typical behavioural or physical signs of pseudopregnancy
Within their caseload, the author has personally seen:
- Dogs in the second category present with dog–human aggression and/or anxiety, dog–dog aggression and/or anxiety, sound sensitivity and even separation-related behaviours (Figure 1)
- Dogs presenting in the first category going untreated and subsequently moving into the second category
- Dogs presenting in either category whether they have experienced an overt pseudopregnancy following the preceding season or not
How do we treat pseudopregnancy in spayed bitches?
The treatment of choice for pseudopregnancy in spayed bitches is cabergoline (Harvey et al., 1997, 1999), and conservative treatment is not indicated as self-resolution is unlikely. Cabergoline is a dopamine agonist that inhibits the release of prolactin from the pituitary gland. It is licensed at a dose of 5µg/kg once a day (preferably with food) for four to six days. However, 14 days of cabergoline may be required in dogs with aggression-related behavioural signs (Ramsey, 2017). (The author recommends 14 days for any dog with aggression or anxiety resulting from pseudopregnancy which is likely to be all dogs presenting in the second category (above) and some in the first.)
Cases requiring treatment for longer than 14 days have also been seen (Root et al., 2018). When using cabergoline off-licence in this way, there is one unusual side effect to consider in addition to those found in the SPCs/datasheets for licensed products. When used for 14 days or more, cabergoline can change the coat colour of some dogs (Gobello et al., 2003). These changes are transient, and the coat will revert to its original colour after the next big moult (Figures 2 and 3).
It is not uncommon for signs of pseudopregnancy to recur and for repeat treatment with cabergoline to be required, though more than two courses is unusual (Scott, 2000). If recurrence occurs, the author recommends making the second course of treatment as long as or longer than the first. It is also worth checking that clients are correctly storing, measuring and administering the product as compliance is sometimes poor, and/or coaching is not given or done so poorly when the medication is dispensed.
Behaviour modification
In some cases, complete resolution is achieved with cabergoline treatment, and no behaviour modification is required (Scott, 2000). But in other cases, a percentage of undesirable behaviours remain through learning. These learnt behaviours will require behaviour modification under the guidance of a clinical animal behaviourist. In the author’s experience, these dogs are at least 50 percent better (from client estimates) following cabergoline alone.
In some cases, complete resolution is achieved with cabergoline treatment, and no behaviour modification is required. But in other cases, a percentage of undesirable behaviours remain through learning
Other considerations when treating pseudopregnancy in spayed bitches
In cases resistant to cabergoline treatment, it is worth considering hypothyroidism as an underlying cause. This is because an increased release of TRH can cause an increased release of prolactin, and there are cases of lactation reported in hypothyroid dogs (Cortese et al., 1997). However, attempts to prove a direct link between hypothyroidism, prolactin and behaviour changes in dogs have yielded contradictory conclusions (Hrovat et al., 2019).
It is also possible to see an overt pseudopregnancy (with physical and/or behavioural signs) in a spayed dog with an ovarian remnant. In these cases, any behaviour changes are cyclical (Scott, 2000) rather than persistent. These can be diagnosed with hormonal assays, ultrasound and/or CT scans.
Can we prevent pseudopregnancy in spayed bitches?
The good news is that persistent pseudopregnancy is largely avoidable with due consideration of the timing of spaying.
Persistent pseudopregnancy is largely avoidable with due consideration of the timing of spaying
Harvey et al. (1999) suggested spaying prepubertally as no dog can enter persistent pseudopregnancy without having ovulated and entered metoestrus. However, the steady trickle of research papers in the last decade or so is moving the veterinary profession towards neutering later due to the behavioural implications of neutering (which is also the author’s recommendation).
When should bitches be spayed?
Spaying is contraindicated in overt pseudopregnancy (Gobello, 2021; Harvey et al., 1999; Root et al., 2018) and in metoestrus for those dogs without overt pseudopregnancy (Harvey et al., 1997, 1999). This latter instance is why we are taught to hold off for three months after a season before we neuter bitches. Despite this, it is common to find cases where neutering has been recommended by vets three months after the start of pro-oestrus instead of three months after the end of oestrus, resulting in persistent pseudopregnancy (Figure 4).
In one retrospective study of 28 spayed bitches suspected to have persistent pseudopregnancy, the majority were spayed within the first four months after their season, with a small number spayed five to six months afterwards (Harvey et al., 1999). This may suggest that a very low progesterone concentration may persist into anoestrus in some bitches, and its sudden removal precipitates persistent pseudopregnancy.
Alternatively, perhaps the length of metoestrus is much more variable in some individuals. The authors of the study concluded that in clinically normal bitches (without an overt pseudopregnancy), spaying should be delayed until at least four to five months after the season, whenever possible.
Given the average inter-oestrus interval is seven months and the average length of a season (pro-oestrus and oestrus) is 18 days, spaying four to five months after the end of a season is tight but achievable. Of course, not all dogs follow textbook timings, and we don’t always know the inter-oestrus interval. Consequently, this author recommends 16 weeks after the end of a season as the “sweet spot” to neuter most bitches. This period will still trap some bitches in persistent pseudopregnancies, but this will be a smaller number than at 12 weeks after the end of the season. To assist in the estimate of this sweet spot, owners should be encouraged to record the date they first see blood-stained discharge or a swollen vulva.
The impact of laparoscopic spays
Spaying in the four weeks immediately before a season is usually avoided due to the increased vascularisation of the reproductive tract. However, vets performing laparoscopic spays are not as concerned about this as laparoscopic access is less likely to inadvertently rupture the ovarian blood vessels, meaning they could wait longer than 16 weeks. If the spay occurs before ovulation, the risk of tipping them into a persistent pseudopregnancy is avoided. Hence with the laparoscopic procedure, it’s possible to spay in early pro-oestrus.
Preoperative checks
The author highly recommends a preoperative check before or on the day of admission for all bitch spays so bitches can be screened for lactation and mammary enlargement. The caudal pair of mammary glands are the most fruitful, and any liquid, whether milk-like or not, should be interpreted as a positive lactation test. Owners should be questioned about the behavioural signs of pseudopregnancy.
The author highly recommends a preoperative check before or on the day of admission for all bitch spays so bitches can be screened for lactation and mammary enlargement
Surgery should be postponed if a bitch is found to be pseudopregnant at the pre-op check. Following this, the vet should wait for all signs of pseudopregnancy to self-resolve and then check again before spaying or treat with cabergoline before checking again and then spaying.
Ceva (n.d.) advises a wait of seven days after the last dose of cabergoline before spaying to allow a few days for the medication to leave the body and to ensure the pseudopregnancy does not return. However, the author is not convinced that all recurrences would show in that time, so prefers to wait 14 to 21 days. Further, cabergoline can be used to induce oestrus, so do not wait too long, or both dog and client could be stuck in another cycle.
Welfare implications
Dogs under three years old are at a proportionately high risk of death from undesirable behaviour (33.7 percent) compared with other specific causes of death (Boyd et al., 2018). One study showed that the most undesirable behaviour in dogs is aggression (54 percent), and the fifth is anxiety (5.3 percent) (Boyd et al., 2018).
Given most spayed bitches are likely to be neutered by the age of three, how many of these aggression and anxiety cases were related to persistent pseudopregnancy? How many are going undiscovered, untreated or being relinquished to already overburdened shelters? How many are being exposed to the unregulated behaviour and training industry, rife with practitioners whose awareness of clinical issues and their effect on behaviour is questionable and whose methods of resolving behavioural issues can be ill-informed and ineffective?
The welfare of individual bitches, and maybe even bitches at a population level, is suffering for want of recognition of a clinical problem that presents behaviourally, and which is not only treatable but, more importantly, largely avoidable.
