My neutered male rabbit is acting hormonal and spraying everywhere.

Question
Hello Dana, We have had our two male house rabbits (brothers) since they were 3 months old. They're now 5. We had them neutered at 1 year old and that seemed to calm them down a bit. They've been pretty much litter trained since then with the old incident of weeing or pooing somewhere they shouldn't. One rabbit has always been the dominant one and humps his borther now and again. But about one month ago, we noticed the less dominant one was chasing his brother around A LOT trying to hump him. This has got increasingly worse with it happening every few minutes while we are around. In the last couple of weeks he has also been pooing all over the house and weeing too. He also seems very excitable when we are around. They have always done a happy grunty sound and run around in circles when they're happy. i.e. about to get treats etc but he's doing it every time we are there for seemingly no reason. We have had to limit them to two rooms of the house so the carpets don't get ruined but really don't want this to be for very long.

We have spoken to a vet but he's at a total loss as to why this could be happening. Is it possible that after 4 years of having the op, some hormones have been released again if the op wasn't performed correctly? Or is there something else that could be making him behave like this? We're worried that his brother is going to get aggressive if this carries on and this will permanently damage their relationship. Oh, forgot to say, we have separated them for an hour at a time just so the non horny one gets a break! Sometimes he goes and sits upstairs on his own but other times he seems to want to get back to where his brother is. Any advice would be much appreciated, we don't know what to do next!

Answer
Dear Emma,

One possibility for recurrence of hormonal behavior in a neutered male is an adrenal tumor.  These are usually not metastatic, but they can cause all kinds of problems, such as the ones you are describing.  This can be diagnosed via radiography or ultrasound.  A blood test for hormone levels might also be instructive.

Fortunately, treatment with Lupron is often very effective at alleviating the signs of this disorder, so you might wish to ask your vet about that.

I hope this helps.

Dana