I recently arrived at the vets with two bitches to be spayed. One I had picked up that morning from a home and was coming into rescue. The other was from a potential fosterer who I had spent months persuading to have her dog spayed.
When I went to book them in only one dog was expected (I had mucked up) and as they had a very full operation list they could only do one with the other being done 7 days later. Not spaying the rescue would cause major problems as this would affect her going to her foster home a few days later. Not spaying the other would not have been a major problem but just inconvenient for her owner.
I decided to go with the potential foster home dog and rearrange the op for the rescue. After badgering the owner to have her bitch spayed I really did not want to put her out.
I had a call later in the morning to say that her womb had the beginnnings of a pyometra and contained horrid gunk. There are two types of pyo, an open where the discharge drains and a closed where it just collects in the womb often not noticed until it is too late. Both are potentially fatal but the closed especially so because the damage is done before the owner realises thaere is something seriously wrong. A week later may have been too late and that operation on that day may well have saved her life.
I don't know what made me chose one over the over. The second had her op a week later and all was fine and she is fully recovered. The fosterers dog has now had the all clear after a course of antibiotics.
Just a lucky call I guess