Should a tailless litter be culled
I don’t really have one simple answer!
Genetically, tailless/manx mice are the result of a dominant gene (at least in the US), so one of the parents would have to be manx as well- though just like in manx cats, manx mice can sometimes appear to have an almost normal length tail, so you may not realize until a litter is born and some are missing tails!
Mice that are tailless due to genetics are more likely than normal tailed mice to have kinks in their spine or develop back/spinal problems or hind end degeneration due to their decreased number of vertebrae. This does not automatically mean that it is completely and unequivocally unethical to breed them; rather, it requires much more careful observation than other varieties, and selection for healthier mice with normal, unkinked spines is crucial. If you don’t feel that you are up to this task, you can keep them as pets only and not breed them, or cull them entirely while they are still small. Otherwise, let them grow and see how they fare. Cull any that develop spinal issues or kinks, and breed the healthiest ones.
Sometimes, however, taillessness is not genetic, but rather the result of an overzealous, usually first-time mother, who grooms too hard and ends up nipping off her babies’ tails (or ears... or feet... I’ve never had that happen but I’ve heard horror stories from others). If both parents appear to have normal tails- excessive kinks may indicate possible manx lineage- and you’re seeing lots of tailless mice, I might suspect that the babies are not true manx but have instead been snipped by mom when you weren’t looking. Newborn pinky mice heal fast and you may not even see any blood.
In the case of mice that are not truly manx but instead just have been docked by their mom, there is likely nothing to worry about as they do not have issues with shortened or kinked spines. So there’s no need to cull the litter (unless you don’t like the aesthetic of no-tailed mice and have animals to feed anyway).
I hope that helps!
