You might have to house them individually. It will cost more, but it means they won't be able to harm each other. Males that have been raised in the same litter (and never used for mating) can sometimes co-habitate, but it depends a lot on the strain.

this link is useful

https://pethelpful.com/rodents/alphamouse

regards

Thank both of you , i'll check it out

I agree with@Kati A Clark.

Wish you good luck.

Thanks !

If the adult unfamiliar males are plased together into one cage, they will usually fight. This is a great social stress, which affects the biological characteristics of animals.

The maintenance of animals for a long time in individual cage will prevent fights, but within a month will cause the development of the social isolation syndrome, when the most of mice will be timid (depressive), which is also not good for the experiment.

To allow the males to grow up together without fights for a long time, they should be kept in the same group after the seperation from the mothers, without mixing the group.

Hi Marcela,

C57Bl/6J or N mice are indeed a relatively aggressive strain, it would be much easier to handle Balb/c, CD1, B6D2, 129Sv mice.

Still, if you manage to keep your own colony and generate litters yourself, with a timely weaning at around P20-P21, placing 3-4 males together at that age (whichever the litter origin, before sexual maturation they make no distinction between different litters) in a sufficiently large cage (the best for keeping mice in a social environment is to use the very large cages that were used once, something like 40x25 cm... but that's difficult nowadays), let's say 500 cm2 (the Tecniplast standard size), they should in average age pacifically together. Adding some cotton and some toys will always help. You will anyway have a cage once in a while where mice will not cohabit (when this happens there is little you can do, it means they don't accept the social hierarchy and all want to be alpha), but the majority of the cages should make it.

Good luck!

Hi everyone,

Thank you for your advices, so far, I've only separated two alpha males and 3 mice that had been bitten and beaten pretty bad, these are all kept apart, each one in a cage (they're getting better).

The rest of them (around 26) are still kept together in their cages (about 2-3 per cage).

When I started to notice this kind of aggression was when they had only been a week in our facility, maybe the stress from the trip and the change of environment had something to do with it? They're young mice, about 5-6 weeks old.

Anyways, they seem to be better now, no signs of aggression in the last 2-3 days in the rest of the shared cages, could I incorporate the hurt ones once they get better in a single cage? (they used to be in different cages)

Thank you everyone

Dear Marcela,

If you will place isolated males in grouped cage, fights may arise again. The decision what to do in this situation depends on the design and aims of the experiment.

Thanks again Natalia

Marcela, after 6 weeks of age it will be almost impossible to put any wt isolated mice together, even if they were together before, they don't have a social memory of this kind. Even littermates if you isolate them, you cannot put them back together after they reach sexual maturity, around 40 days of age.

Indeed a transport and the change of environment is a stressor, so it is possible that this has triggered some reaction. Anyway as I was mentioning you'll always have a cage once in a while where the male won't cohabit pacifically, that's the variability of nature.

Cheers.

I agree with Сolleague. If the design of the experiment allows, it is possible to put all males with females, preferably sterile (1 male - 1-2 females in one cage). But it depends on aim and design of experiment.