Concerned about health of new pup

Question
My gerbil pair had two pups 22 days ago.  No problems at all and they both seemed very healthy.  Mom and dad gerbil are wonderful parents.  HOwever, I notice a huge difference in the two pups.  One pup is almost twice as big as his brother.  He has a full coat of shiny black fur and is very strong and active.  The little one has a faint white coat coming in and there is actually an area on his back in which there is no fur coming in.  It almost looks like a hairless stripe down his back.  He just overall seems weaker..but he's hanging in there. He nurses and explores the cage.  i wonder if he is a runt?  Anything I can do to help him nutritionally?

Many thanks!

Leigh

Answer
I have received a lot of emails lately about a runt gerbil. Its normal, and sometimes they don't make it. Don't think that just because they have their hair now that they've past the danger point. I've lost pups at 6 weeks old that were the runt of their litter. Sometimes it can be a genetic problem, could be outcompeted for food or just not fighting to live. Good luck.

Ashley