Could womb risk kill dog?

I am unsure whether to have my 18-month-old mixed breed dog spayed. My vet advised that without the operation there is a risk of a womb infection in later life, which can be fatal without emergency treatment. What are the symptoms and how big a risk is it?

- With DAVID GRANT

The medical name for this condition is pyometra, meaning pus in the womb. Vets generally abbreviate this in clinical notes to 'pyo. It is a very common condition in older female dogs that have not been spayed.

Early signs can be subtle, leading to delay in seeking veterinary treatment. Initially the dog may be subdued with a decrease in appetite, lethargy and increased thirst.

This usually occurs within a few months of the previous oestrus (heat). There are two versions of pyos, open and closed. The former means the cervix is open resulting in a discharge, which makes the diagnosis quite easy and hopefully obvious to most owners.