fighting between cagemates

Question
I have two male rats, Basil, who is about a 14 months, and Herbie, who is 9 months.  When I first brought Herbie home, I had him in a separate cage located beside Basil's, so that they could see and smell each other yet not touch.  After a week or so of this, I began letting one out to play at a time, allowing the one at play to interact with the one currently caged yet keeping a cage between them for safety.  At this point, Herbie, who was considerably smaller than Basil, wanted to interact with Basil much more than Basil did.  Basil began spraying, but stopped within a week or so.  My next step was to switch their cages.  I would put each in the other's cage for an hour or so and then return them to their own.  Basil again started spraying, but stopped after a week or so.  I then let them both out to play at once, standing by to separate them if needed.  There was only one fight that I felt compelled to intervene in.  After they'd been playing together for an hour or so a day for a couple of months, I put them both in the same cage (Herbie's)and again they had one incident where I had to clap my hands together to get them to separate but other than that, they got along and would frequently lay together and share a nest box.  I had a family emergency shortly thereafter and brought both rats with me on a road trip, still in Herbie's cage.  A month later, when we returned home, I joined both cages together (custom cage I made which converts into one portable cage (Herbie's) and one large non-portable cage(Basil's) and allowed both rats to have free roam of the entire large cage.  Around February, Herbie, at six months, began trying to mount Basil.  This wound invariably trigger a quick snap or push from Basil, after which Herbie would squeak and run to a different level of the cage.  I figured this was just juvenile hormones and the phase would be outgrown.  It did seem to get better for a while, but now, they're having an all-out war and both of them are marking their territory something fierce. I don't actually see them fight very often, but recently I noticed that Basil has bite marks on his ears and an abscess on his snout while Herbie has bite marks all over his snout, neck, and jaw.  I have a vet appointment for both of them, as I'm obviously concerned about Basil's abscess, but also the severity of the bites on Herbie.  I've separated their cages once again until I can figure out what to do.  They did still occasionally share space and sleep together until I separated them.  In fact, just before I noticed their injuries they were cuddled together in a nest.  Herbie seems to instigate most of the fights, if that makes a difference.  Anyway, I don't know what to do now.  I don't want them both to be alone for the rest of their lives, but I don't know what to do to help them to get along.  Any advice would be tremendously appreciated.

Answer
Herbie is a juvenile male and you correct hormone play a large part in it. He is trying to assert his dominance and both rats want to be dominate. wait until Herbie is a a few months older until putting them both together in a cage again. He may need to mature. Continue the intro step to keep them familiar with each other. I am amazed that you were that knowledge about introductions and you are doing a great job. Continue with them and in about 2 months try putting them together again.

Good luck!

Emily Harris