I felt there was a difference, but I had to go to the dictionary to find out: if I understand well, "
casco" is only used for horses, as that's where you fix the horseshoes ("herraduras"). Yet, I have heard people from the country say "cascos" also for mules and donkeys, which are animals that also "wear" hoof protection sometimes... not for oxen though, even if they also can get their own "shoes".
"
Pezuña" is the general word to speak about the foot of all hoofed animals.