It has been suggested that pyometra is a condition of middle aged and older dogs.22-25 However, pyometra has been reported in dogs as young as 4 months old and as old as 16 years.4,12,22 A study from Japan of 165 colony-raised beagles revealed a prevalence of 15.2% in nonspayed female dogs over the age of
4.23 In this study, the average age of onset was about 9 years. A Swedish study reported the prevalence of pyometra at about
25% in intact, publicly owned female dogs under the age of 10 and about 2% in bitches more than 10 years old.24 In yet another survey, the mean age of dogs presenting with pyometra was 2.4 years.12 The younger age was attributed to the frequent administration of estrogens for mismating in this population.
Pyometra can occur in any breed of dog. Breeds thought to be predisposed to pyometra include rough-coated collies, rottweilers,
miniature schnauzers, Cavalier King Charles spaniels, golden retrievers, Bernese mountain dogs, and English springer spaniels.16,24,26 Breeds thought to have a decreased predisposition to pyometra include Drevers, German shepherds, dachshunds, and Swedish
hounds.24 Not all studies have confirmed a breed disposition.9 Meanwhile, previous pregnancy has been reported to be protective in some dog breeds but not in all.22,26
The clinical signs associated with pyometra typically appear one to three months after the completion of estrus.6,7
Most of the clinical signs are not specific for pyometra, including lethargy, depression, pyrexia, anorexia, vomiting, diarrhea,
polydipsia, and polyuria. A serosanguineous to mucopurulent vaginal discharge can be seen if the cervix is open. Vaginal discharge
may be the only clinical finding in some patients.
In patients with closed-cervix pyometra, vaginal discharge may not be present. Dogs with closed-cervix pyometra are often
more seriously ill at the time of diagnosis than those with open-cervix pyometra.16 A closed cervix inhibits the elimination of the infectious uterine material, delaying the recognition of illness and increasing
the likelihood of complications such as septicemia, endotoxemia (most commonly associated with E. coli infection), and septic peritonitis.5
Bacterial contamination in cases of septic peritonitis may be the result of uterine rupture, translocation of bacteria across
the diseased uterine wall, or, less likely, oviduct leakage. More severely afflicted closed-cervix patients may present with
signs of shock, dehydration, or collapse.5