I didn't know that, since my research generally tends to be, well ... general! You don't need to go out of your way to find out how common that is, but it's interesting that there might be an out-clause (oh ho) for Santa and the maleness of his reindeer.

If it's possible (and yes I realize I am discussing the laws of imaginary science), then perhaps the reindeer are a mixture of immortal male and female animals that never age once Santa chooses them. I imagine Dancer, Prancer, Comet, and Vixen could be female, while Dasher, Donner, Cupid, Blitzen, and Rudolph could be young males.

One thing I learned in my deer research is that the antler-shedding mechanism is thought to have evolved in order to give each male a fighting chance again the next year if their antlers should break or be otherwise damaged during mating season fights. If that's the case, perhaps males who are too immature/young/small to fight for a mate wouldn't need to replace his antlers, and might just hold onto them until he grows up enough to get into the fray properly. Neat idea, anyway.