When i got my little girl from the pet store she had cuts all over her tail, i noticed a bunch of males trying to mount her which caused more cuts. Are your rats all housed together? maybe they are trying to mount each other? if it's not that i would check the cage for any sharp edges. Other than that.... it could be they are cleaning their tails too roughly?
hve just looked in their cage earlyer when i cleaned it and nothing sharp i have the 2 brothers toby and cody in the big cage and roob in the little cage i think it may b they are cleaning too roughly altough roob does mount the others but never causes them pain when he does!
Your rats could possibly have mites. Do they have any cuts or scabs on them anywhere else? With the cage that houses two boys, their cuts could be from squabbling with each other, but since all three of your rats have the cuts, that makes me wonder.
Hm... if I were you, I would take them in to the vet for a skin scraping just to see if it's mites. It could also be that they're getting too much protein in their diet (it causes them to itch - sometimes to the point of getting small scratches and such).
It's not so much the mites causing the cuts, the mites itch and the rats scratch themselves to stop the itching and can damage their skin in the process. If you look on the skin behind their ears you might see tiny little scabs from the itching. It is easier to see to the skin if you blow gently on the fur to part it.
If you do see them itching excessively they should see a vet for a mite killing prescription... It is very dangerous to use over the counter flea and mite powders or sprays on rats, but your vet can give you a safe one.
In the meantime, keep their cage clean so that the cuts can heal..