Not sure what happened to your big rats - they only last a couple years though, so maybe it was age?

The head tilt signifies an ear infection. It could be something else but the ear thing is most common. A vet could get it fixed. I don't know any OTC treatments.

The dumbo gene is recessive.

Try to avoid breeding rats that have white wedges in their face patterns, as they tend to have babies that can't survive. For more info, look up "megacolon". Albinos, or PEW (pink eye whites) are not associated with this problem.

If your male was struggling to breathe, remember that these animals have very high metabolisms and are at risk for fatal respiratory inflictions if their air is not well ventilated. What kind of cage do you keep them in? Do you change their litter or bedding often? What are you using for substrate? All of these things can have a major impact on your rats' lifecycle, especially on the older, less robust ones.

Good luck.