A spay is just another surgery with a good
vet. It is more invasive because it goes into the body cavity, but its a standard procedure unlike a tumor removal which often occurs when a rat is older and less likely to deal well with surgery, plus the vet has no clue what they will find until they go in.
I would spay all my girls if I could, and did have a control group of 10 spayed girls. Only 1 died of a tumor, and it was cancerous not a benign mammary tumor.
A friend of mine (jorats) actually spays ALL rescue girls that come through her door, and has spayed rats over 2 years old, its all to do with health really. There is a study of hers that was posted here...
Its fascinating and shows the results in a pet rat community rather than lab conditions.
But she has an excellent vet, I have a wonderful vet, etc...you have to find a good vet for spays.
For yourself I would say I wouldn't spay your 2 older girls but would get the younger rats done as it can benefit them much more. You can spay the 18 month'ers, I have done it, but the actual benefit may be less.
As for the spay itself...Today am taking in a 10 month girl for a tumour removal and a spay to prevent more.
My vet does pain meds prior to, during and after surgery (anesthetic is isoflurane), and I take home metacam (pain meds are a must, since they can cramp up afterwards, for a day or so...mine usually only get metacam for a day). I also prefer to use oral abs (baytril) for 7 days to prevent any infection.
My vet and I have discovered that I and my girls prefer internal dissolvable stitches, and external glue...they don't bother it like they would with external stitches or staples. It heals fast and there's no recheck on our part
I pay about $170-200 for a spay (Canadian prices are always higher), but sometimes she gives me rescue prices as well.
Rennie's spay incision