Uterine wells in canines

Cow's uterus

This article follows on from a (ultimately rather heated!) discussion in our Facebook group. Both our beginners’ and AUA-members-only groups are forums where scanners-in-training and established scanning professionals, respectively, can safely and privately discuss any topics which arise in their work. No members of the public or potential clients are able to access the group, keeping this as a safe space for discussion between animal scanners, veterinarians, vet nurses and sonographers.

‘Wells’ in bulldogs:

This discussion is reproduced with permission and was prompted by a scan performed by one of our members. Following a scan of a bulldog, it was reported that there were no foetuses on the scan, but there was a significant amount of fluid clearly visible, surrounded by what appeared to be uterine walls. This is unusual to see in dogs, because the uterus is so very small (in comparison to cows whose fluid-filled uterus is easily visualised in and around oestrous).

Above: fluid-filled feline uterus, which would be similar in size to the uterus in smaller dogs. The ovaries can be seen at the end of the two horns. The CE markings of the dish give some idea of scale.

Very experienced scanners may be able to visualise fluid within the uterus during and around a bitch’s season, but it is challenging because the amount of fluid is minimal. Most people who do see the uterus as the bitch comes into season only do so in their own dogs, with whom they are very familiar as they have been performing serial scans on them. In contrast, in the scan in question, the bitch was unfamiliar to the scanner and the amount of fluid was very pronounced.

Cow's uterus
Above: Despite being totally empty, the uterine horns in this cow are still very visible. This is in contrast to dogs, whose comparatively tiny uterine horns are very difficult to see on ultrasound, even when in season. UC Imaging also shows an image of a fluid-filled uterine horn here.

When the professional canine scanner recommended a trip to the vet to rule out pyometra, the owners – very experienced bulldog breeders – explained that they believed their pet must not have been having a true season when she was mated 30 days ago, and that this was now her proper season. Many bulldogs (including this particular bitch), they explained, retain the fluid due to their body conformation, and need to be ‘drained’ prior to mating – and this must be what could be seen on the scan.

The scanner again reiterated advice to see a veterinarian and asked the breeder to stay in touch.

This experience was then recounted to the group, and two breeders confirmed that they, too, had heard of this phenomenon. They explained that some bulldogs can suffer from ‘wells’ (anecdotally worse after having already had a previous litter), which can be drawn out with an AI tube, with 20-100ml being reported. Again anecdotally, natural conception was reported as difficult for these animals.

Yvette Lovis, obstetric sonographer, added that human women can suffer from something similar – hematocolpus or hematometra. “Colpus is vagina and metra is uterus,” Yvette explained; “in young woman when there is an imperforate hyman and elderly women with cervical stenosis.” The general consensus among the medical professionals of the group was that this was not a normal variant and warranted veterinary attention. Chris Allen, a veterinarian-in-training and author of vetschooldiary.com explained that, as muscular tissue, the uterus empties through contraction. Any failure of this to occur is pyometra, warranting a trip to the vet.

Yet, the experience ‘on the ground’ seemed to be different. Another scanner joined the conversation explaining that “pooling is common in other breeds, I’ve experienced this with two Staffordshire Bull Terriers and a Cavalier King Charles too.” Another scanner joined the conversation to add that she had heard of wells in the tract and discovered this phenomenon incidentally during transvaginal artificial insemination, but not in the uterus itself, as nobody she knew was performing transcervical AI. She put this forward as an interesting theory that perhaps this is why this condition was not, in fact, strictly pyometra.

So are wells pyometra, or something different?

An extensive search of the literature brings up few references to these “wells,” whether uterine or vaginal. Chris Allen provided a great starting point, stating that “there are Cystic Endometrial Hyperplasia and pyometra and hydrometra which all will show with fluid in the uterus,” yet none of these conditions seem to exactly match the description of these ‘wells’.

So, the jury is still out on the exact origin of wells in bitches in season, and this page will be updated as new information is found. The only thing that we can be sure of as scanning professionals is that we are not in a position to judge whether or not these wells are safe for the dog in question, regardless of her breed or how frequently we may have encountered it before. Anything we find which is outside of the scope of a normal pregnancy scan warrants referral to a veterinarian. What the owner chooses to do based on their own experience and the history of their animal is outside of our control.

Related conditions / further research:

– Cryptomenorrhea / cryptomenorrhoea

– Surgical Pathology of the Canine Reproductive Tract – by Dr Rob Foster, sadly this link appears to now have been removed from the University of Guelph website, but previously detailed just about every pathological condition of the canine uterus (includes some pictures), along with references to aid further research.


If you are an AUA member and cannot access a particular journal article that you need, please contact us for help.


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