Telling the Boys from the Girls in four day old baby mice
Like 3 Dislike 0 Published on 4 Oct 2019
A very short video that some of you may find interesting and useful.
These are Snow's babies, who are growing up very healthy. There are 5 girls and one boy in her litter. I was hoping for two boys, having so few boys in a litter is rare. But otherwise I am very happy with this, boys are more expensive and difficult to house than females, overall females are easier to keep. Do love the little boys though, just that they are more of a luxury to keep, especially since my vet has upped the cost of neutering to $200 :P This little boy will be used for breeding, so I will have to keep him intact (and alone) for at least six months. Although I may in future not have to keep them alone, I have found a mousy birth control powder and will experiment with it to see how it works. If it does work and there are no bad side effects, the days of lonely breeding males will be over :)
Determining gender in 3 to 4 day old baby mice is not difficult, once you know what to look for. Between newborn and 3-4 days old, all baby mice look like little boys. This is because the amniotic fluid they were immersed in for so long in their mother's womb makes everything swell. After 3 to 4 days the swelling has gone down and now it is easy to tell the difference. The urinary papilla in the boys remains prominent, in the girls it recedes to almost nothing, their urinary papillas are very small and flat. The other distinction is the distance between the urinary papilla and anus. This distance is much longer in the males than in the females. Sometimes if you look closely, you can also start seeing nipples, these are only present in the females. When the babies first get fur at around 10 days old, the nipples become much more visible and telling gender becomes even easier.
Warning: do not breed mice unless you are an experienced mouse person and know you will be able to keep all the babies (especially the males, who will either need to be neutered or be all kept in their own individual cages) or know there are good homes waiting out there for them. If not, all you will become is an animal hoarder with way more animals than you can care for properly. You have to breed responsibly or not at all. Otherwise you will just be bringing little mice into the world to suffer.