24% of dogs die from an infected uterus if not spayed according to one study. The death can be very painful so it is important to spay your dog so that she can stay healthy!


Pyo is Greek for pus.  Metra is Greek for uterus or womb.  Pyometra literally translates to pus in the uterus.  The process of pyometra in the bitch or queen starts with an exaggerated response of the cells lining the uterus to progesterone, one of the hormones involved in the estrous cycle.  This process usually begins about 8 weeks past standing heat – the period when the female is receptive for mating.  The glands lining the uterus become cystic and fluid-filled.  If the fluid is sterile, uterine enlargement is referred to as hydrometra.  Secondary bacterial infection is favored in this fluid environment and occurs in most animals.  The bacteria usually ascend up the uterus from the normal bacterial flora of the vulva.  Pyometra occurs most frequently in older animal that have cycled through several heat periods.  This is why pyometra in bitches is not as common in the United States as it is in Europe, where fewer bitches are spayed.  A Swedish study reported that 24% of bitches develop pyometra by 10 years of age.  The clinical signs of pyometra include a bloody vaginal discharge in cats or a mucoid vaginal discharge in dogs.  These animals may show no signs of illness initially but severe septic shock and kidney damage can develop.  The usual diagnostic vaginal discharge is only seen if the cervix remains open so the fluid can drain.  In many animals the cervix closes thereby trapping the fluid inside the uterus, which subsequently enlarges and becomes toxic.  The uterus may deteriorate and rupture; a dire consequence.  The immune system responds by sending waves of white blood cells into the uterus in a futile attempt to contain the infection.  This massive amount of inflammatory debris can plug up the kidney’s filtering system damaging the kidneys; renal failure results.  Clinical signs of illness from pyometra include a purulent (pus filled) vaginal discharge (if the cervix remains open), lethargy, decreased appetite, abdominal distention, increased drinking and urination, vomiting and, occasionally, diarrhea.

Spaying is the preferred treatment.  Medical treatment with antibiotics and uterine flushing is marginally effective at best.

Yet another reason to spay at an early age!

Richard Speck, DVM