Size of the dog really has no bearing here as the physiology of dogs are the same. I recommend leaving it as long as possible at least 1-1 1/2 years.
We are learning a lot these days thanks to Vets and Universities publishing these studies.
My own vet says leave as long as you can and if you don't have to spay then no one is forcing you to, as long as you assume full responsibility for the dog.
If it's a breeding female the risks of breast cancers are higher. |