From this website:
Can it possibly be true that none of Santa's reindeer can be males because science says male reindeer shed their antlers before Christmas, and Santa's sleigh-pullers are always depicted with antlers?
Well, look. If we're really going to let science be our guide in this matter, the first thing we'd have to admit is that reindeer can't fly, much less haul a jolly fat elf around in an airborne sleigh. If we start down that slippery slope, there's only one conclusion we can possibly reach: Santa Claus doesn't exist, that he's a myth, a figment of our imaginations, a pretty story we tell children and nothing more. That way lies madness.
Thankfully, there's a loophole.
It's a fact, reindeer experts say, that both the male and female of the species have antlers. A male's antlers can measure as long as 51 inches; a female's, 20 inches. It's also a fact that while most cows (female reindeer) retain their antlers until spring, most bulls (male reindeer) drop their antlers by early December. Which is worrisome, I know, but the key word is "most."
The experts go on to explain that a few younger bulls, depending upon hereditary and environmental factors, may keep their antlers well into spring — even as late as April.
So it's plausible to suppose that if, for the sake of argument, there were a Santa Claus, and if, for the sake of argument, he did circumnavigate the globe in a reindeer-powered flying sleigh every December 25th, then at least some of those reindeer — including one in particular with a shiny, red nose — could be males. The logic is sound, and so is the science.