Sorry to hear about the dead one, it could have been a still born or the mom could have kinda ignored it. My rat who just had a litter was giving birth to each baby in really close succession so that she couldn't finish cleaning one before another came, causing her to give a few licks to the newest one and ignore it.

I had to take one out and stimulate it (taking a wet q-tip and rubbing its body, imitating licking) for a few minutes to get it breathing well, and I had to bring the mom's attention to one she had just birthed who was still mostly in the birth sac. I take out the babies once a day and potty them, since she doesn't always get to every one.

Rat genetics are crazy! My albino girls last litter consisted of 1 hood, 2 black berkshires (like their daddy), 7 albinos and one boy who has developed himalayan/siamese point markings who had been just a normal albino until a few weeks after birth. Both of these rats are from petco so I didn't expect anything other than hoods, blacks, and albinos!