Male fancy mice

Male fancy mice are usually more curious and get tamer than females. But keeping them cannot be recommended without restrictions. This text will introduce you to this difficult subject. But take care: what is said here is true for most of the males, but there are exceptions. you just never should count on the chance that your males are among these more amicable mice.

Hurt after fights

As long as the males haven't reached sexual maturity they live together in harmony and peace. But when they reach maturity problems usually start (sometimes even a bit later). You will notice first aggressions. It doesn't matter if they are relatives or rather have grown up together or not. Sometimes groups continue to live together peacefully after sexual maturity is reached and only start fighting after a year or even longer.
Once blood has been shed you needn't hope that they will stop again. On the contrary: fights will occure more often and will get more serious and that will increase stress for all members of the group.
Now there are only two ways to solve the problem: You seperate the fighting mice or you see a vet to have them neutered. Seperating them until you are left with single mice is not acceptable since male mice are social, too. After neutering, aggressions will calm down according to the reducing hormone level. The group can stay together and you don't have to look for other mice species as friends or even long ago neutered male fancy mice. Above that other species are at best a makeshift solution for compagnionship. If you can take them to a vet, neutering them is the best way.
Some people think aggressions can be avoided by using small enclosures in the size of 60 x 30 cm up to 80 x 40 cm. But this doesn't work reliably. In most cases aggressions will develop in such small spaces, too.
Cages of this size are also not suitable housing for fancy mice. Keeping a group of males in it in the hope that they won't argue is unacceptable!

The bucks will sustain very serious injuries, if you don't intervene - serious injuries with permanent consequences such as scars, permanent hairless spots, sometimes even disabilities are the result. The bucks don't bite into the testicles only. Especially the abdomen with the lower legs, but also the shoulders are typical places with cumulative injuries from bites.

Poor victims - these bucks didn't survive the massive aggressions in the group and paid with their lives. They rarely die from the injuries they received. The majority of them dies of the immense and permanent stress the aggressions cause.

This is a challenge even experienced keeper will not succeed in! Don't try! In more than 95% of all cases it will fail and in the end you have some single mice which may have gotten hurt.

Your mice argue and are about to get neutered. What should you do up to the date of the operation? This is the most difficult time for you and the mice.
It would be the best if the males stayed together. If the date at the vet is not more than 4 weeks (or a little later) in the future you can move them to a smaller cage. If they still fight, remove any furniture.
Keep an eye on the mice. If they run after each other and/or there are some single bloody bites it might be best to move them to an even smaller cage to prevent further or even more serious aggressions.
Separating them would be the solution for extreme cases. You can't introduce them again the first time after the operation. So you will have only singles, one in each cage for at least weeks.
Separation is unavoidable if there is at least on mouse showing a high level of stress and/or the males hurt each other seriously. To find the right time is difficult. It can differ a lot from case to case. If you are not sure that the conditions in the group are still acceptable it's better to seperate them sooner than later.
The time before and the first weeks after the operation are the more stressful the more the males fight. So act quickly when you notice your mice fighting and bring them to the vet as soon as possible. Otherwise there won't be any way back to harmony!

Please note: The level of aggression of recently neutered males can rise within the first 2 weeks after the operation. Not until the 3. week aggressions and fights will decrease.

Neutered and unneutered males can live together in harmony. If they decided that they like each other it is unlikly that they will start fighting later on, as long as there is only one unneutered male in the group.
If there is more than one unneutered male in the group there is a high risk that aggressions among the unneutered males may occur. The neutered ones are usually not involved in the fights. But if possible you should bring the fighting males to the vet to have them neutered. If they are not fit or too old for the operation you must seperate them and get them new friends.

Such introductions are a bit difficult, so it would be better to be experienced in mice behavior if you try it. If you have little or even no experience try to get advice and help from experienced keepers or don't try to introduce them.
Such an introduction may work but it is not guaranteed. Don't try to introduce neutered males within the first 4 to 8 weeks after the operation to unneutered ones. Usually the unneutered react in an aggressive way as if the new partners were still unneutered. Also the neutered males may get aggressive towards their new cage mate(s).
From the third month after the operation chances of harmony after the introduction increase. But about 50% of all cases still fail. But the more time has passed, the higher is the chance of a succuessful introduction.
About 6 month and more after the operation there's a quite good chance of a successful introduction. Now a try is really recommended even though it might be better if this is not your first introduction of fancy mice. If you are unsure to how do it, ask for help from experienced keepers.
The introduction of neutered and unneutered males is more difficult than the one of females among each other or females with neutered males. Choose the step-by-step-method and provide for two weeks or more time. If you are unsure whether the group is ready for the next step or not take a little more time on each step. Otherwise there is a significant risk to fail in the end.

Neutered males are peaceful among each other after reaching a low hormone level. This level is reached after about 4 to 6 weeks. Fights and aggressions are unlikely after the group has calmed down.
Neutered males show a behavior similar to females. The more time has passed since the operation the more compliant the males are.
However within the first two weeks after the operation aggressions might increase for some days. If there were fights and aggressions before the operation keep in the same cage them as before for two or three weeks.

Introducing neutered males is the more easy the more time has passed since the operation.
Newly neutered males up to 6 weeks after neutering still may react like unneutered males to each other. So you should wait a little longer.
From 8 weeks chances of a successful introduction get better and better. And from 3 to 6 month after the operation prospects for a successful introduction are good. If you want to try earlier you should already be experienced in introducing fancy mice.
If you want to reunify individuals that fought heavily before neutering you should let at least 4 month pass by before trying. Otherwise they might be still very aggressive towards each other. A better solution would be to introduce them to other mice because 4 months would be a terrible long time to be alone!

Neutered males and females usually live in stable groups. Especially if you keep many females neutered males are a good idea to avoid or even calm down quarrelsome females.
Some keepers have a rule of thumb how many neutered males should live together with how many femals. But it became evident that the character of the individuals has much more influence on the harmony in the group than random numbers. So a group consisting of five neutered males and one female can be as calm as groups with five females and one male.
To avoid offspring you should introduce neutered males to females not earlier than 3 weeks after the operation. During the time before they might still be fertile.
But even when they are infertile some neutered males keep mounting their females. This is quite normal, you needn't worry about it. If the neutering was successful, the males are definitely infertile.

Usually introducing neutered males and females is rather easy. So you can use the step-by-step-method with 3 steps (bath tube - transport cage - neutralised enclosure). The introduction will take about 5 to 7 days, although there are some exceptions where it takes longer.
So always keep an eye on your mice if there are any quarrels. If there are serious or many quarrels or outright fights, you probably will need more than three steps and more time than just a week.
Please note: 3 weeks should have passed since the operation of the males!

Sometimes it happens that only one testicle is found. The other one usually is situated in the abdominal cavity. To open the cavity is a high risk for the male's life. That is why a vet usually removes only one testicle in such cases.
Theses induviduals loose only a part of their hormone production which is taken over by the remaining testicle. That's why these males might still be fertile and behave like an unneutered male. Also the other mice will see them as unneutered and will behave accordingly. That's why you have to treat them like unneutered males.

Translation
Angelus Noctis
Proofreading
Jedediah