Hi!
I have read the other response and I don't feel you need to necessarily
euthanise this pup.
I have a pup whose mother chewed off his rear legs and half his tail about a
week ago, he was only just over three weeks old. I removed him and his 2
siblings and kept them together for company. For the first 3 days I gave KMR
but then I gave him human baby food which helped him to be weaned onto gerbil
mix. I have also put tetracycline in the water bottle (which he can still
use) and kept an eye on his stumps.
Other than being smaller than his siblings he is doing fine, he is moving
around considerably well considering he only has stumps, if he makes it to
adulthood he won't have very good balancing skills and won't be able to jump
but he will probably lead a happy life.
I am unsure if he will be able to mate (have difficulty balancing to mount)
but I am not planning on attempting anyway, but I will probably keep him with
his sisters just for the company and to help him out.
I think you should give the little gerbil a chance, I am glad I did as I
expected him to be dead within a day but it has been about 10 days now and he
is much younger than your pup.
Sarah