It is probably result of implicating lamb to sheep and then aliasing lamb to sheep.

Also I'm not sure whether this is a reason why implication sheep -> caprine wasn't fully done.
sheep -caprine is not empty even it is written on sheep that it implies caprine, and I've just saw this

Sheep implies sheep? Who knew?

what

why is sheep aliased to lamb anyway

they're different

KiwiPotato said:
why is sheep aliased to lamb anyway

they're different

Yes and no, Lamb = young sheep
Same for Foal = young horse

You will notice that the majority of gender term or the young is directly aliased to the name of the defaut species.

Stallion/Mare/Faol -> Horse
Bull/Cow/Calf -> Cattle

Besides, I noticed that the RAM and Calf tag is not yet aliased...