Hi Elena,

We have FVB mice and noticed the same problem in males, but not in females. We prefer to keep only 2 male together and try to use them ASAP. Females do not have the issue, as we do not see the fighting issue. Some time, they do not care the pups.

I would suggest just keep 2-3 male together. Notice the dominant male and remove that if fighting start.

Thanks

Hi. Fighting is a common problem. But usually they fight for a few hours when you freshly put them in the same cage and then they calm down and start mating with no further problems.

But if the fighting lasted longer than only a few hours I build a seperating cage myself. This is a cage with a separating wall (steel meshwork or similar). On one side i put the male, on the other side the females. I let them sit like that for a few days. So they can get used to the smell of each other and when you remove the separating wall they tend to not fight that much any more. 

I hope that works for you. If not, try to figure out sources of stress in the room.

Try to establish your group housing before the mice reach sexual maturity (~6 weeks). This should significantly reduce aggression. Also whenever possible, try to co-house only litter mates, especially for the males. This should prevent the mice from becoming aggressive towards one another, and because FVB mice are an inbred strain, it is perfectly appropriate to perform brother-sister matings. If you do start seeing signs of fighting, remove the dominant mouse to a separate cage.

for matings I would exchange bedding and faeces a few days beforehand.

I used to house young mice with mothers until 4 weeks of age, which made them less stressed when they got older. Young females were housed together, also males up to sexual maturty (they start to attack each other after that). If mice are regularly handled, they also get calmer. Mating was done with pairs of females plus a male. I used older males for young females, because they habitually recjected young males, for the reason unknown to me. The best breeding results were in the pairs with an older and younger female, but you don't have to do that (my KOs were autistic-like and I had to take extra care).

Nesting material is ok. Also putting a little house inside, and the cage should be fairly large. This way if they are fed up with each other they can avoid instead of bite. 

I agree with only group-housing littermates straight from weaning, then single-housing the most aggressive ones as needed to avoid fighting. I would also suggest changing their cage less often IF possible. It causes fights to break out among males especially, because their scents have been removed and they need to reestablish their hierarchy.

Most people have said this, but simply, increase enrichment (Nestlet, Igloos, Paper towel roll....) and make sure to have more females than males. Be sure to place the females into a cage that the male has been occupying for at least 2 days.

We work with Swiss male mice that can get pretty agressive as well and changing gloves (or using 70% alcohol) when manipulating mice from different boxes helped diminishing odor exchange and possible agressiveness towards a mice perceived as 'new'. I wouldn't recommend removing the dominant mouse since a new hierarchy will be established by the remaning ones and fights will continue. Also, if you're doing behavioural studies keeping a mice alone is not recommended as mice are social animals. There is a little spreadsheet on mice agressiveness I've found from a supplier, I'll try to attach it as soon as possible.

Hello Elena,

Few comments more I could give you about your post. Fighting wound is a very common finding in males of FVB, but not in females. Mice are social animals so they need to be housed in groups for feeling save, for that reason is recommended to mate or group littermates -mainly if you are working with inbred strains. 

The other part is the hierarchy of the social group and the response to not familiar scent. When you house mice the total size of the cage is important but not so much than the complexity of the cage. Mice feel unsafe in open field, even when you put some nest material as cotton nestlet. They need material for nest sure, but they also need space to be hidden as PVC pipes, or igloos or envirodry material. This last, I normally use in fighting problems, because rodents involve plenty of time working with that material for nesting or making little tunnels. Often I combine envirodry with an igloo in males: the alpha male will be keep inside of the igloo and the envirodry allows the others not being in the visual field of the dominant mouse.

For breeding, I recommend mate one male with not more than 2 females in continuous mating; frequent introductions of intruders could trigger the aggression. It is also useful put some seeds scattered in the bedding  just to induce the foraging behaviour (mainly females).

If you continue observing females fighting, you should consider to talk with your veterinarian to rule out any environmental conditions that could induce maladaptive behaviour in your colony.

Regards

Hoi Elena,

Nice question, I worked for 10 years with all kinds of mice (knockout-, transgene-, ) and our background of mice is the FVB mouse. Good mouselines, good breeding, large amount of pups. But sometimes they fight indeed. We changed the place of cages in the mouse rooms, the male in top of the room and the female down. So, the male cannot smell the female. Always start new breedings with clean cages. The male enters first and ten minutes later the female. Ad enough tissue paper and some food pellets in the cage, also some small "house" of orange plastic. Observe the two mice for half an hour to meet each other. When they start fighting, split them at once. All the mouse rooms have normal music so that the mice are getting used to noise. Handle your mice with care. I hope this is good information for you.

Greets Peter Tooten

Hi guys,

Thank you very much for your feedback, I really appreciate. The problem that I am facing right now: I mate 1 male and 4 females and I am collecting plugs and separate the plugged females in one cage (up to 5 females per cage). If they were grown together from the weaning age they are okay but if the females were from different cages they start fighting especially if they are of the different age. I am trying to organize the cages in way to keep females that used to grow together but lack of space makes me combined different females. So basically right now my biggest problem is females fighting if they are housed together and in the cage with male. I tried to put a nesting material but it  doesn't help too much so probably I will try with towel paper. Thank you again!

The Mouse Cubby https://mousecubby.com/ has been shown to reduce aggression 50 to 90% in mice.