Medieval peasants raised most of the same animals found on a modern American farm (though not llamas!). Theirs were smaller, not having been bred to the enormous size of some modern pigs and cattle. To be a good candidate for a farm animal, a creature had to serve more than one purpose.
So, for example, sheep produced wool, the most common source of cloth in the Middle Ages, and their skin also was used for parchment, the principal material of books and official documents before paper became common in the West in the fourteenth century. Their meat was also eaten and their milk made into cheese. Monks did not eat red meat, but they raised large flocks of sheep for wool and especially for parchment. After all, a big book like the Bible needed a whole lot of sheepskins.
Horses were used principally for riding and, to a lesser extent, for pulling carts and plows. Horsehide produced a heavy leather. Horses, however, were fairly unusual before the spread of horseshoes (see more here), and aristocrats were always more likely to have horses than were peasants, who preferred the solid dependability of oxen for pulling.
Cattle, including both cows and oxen, produced milk and meat and cowhide for leather. Most of the milk would be made into cheese or butter, since milk will not keep well without refrigeration, and cows produced milk only for a short time of the year anyway. Most peasant families either had a cow or would have liked to have one. (Click here for more on cows.)
Pigs were only semi-domesticated. They generally ran wild, rather than being fed at the farm. Their favorite food was acorns, so oak woods were prized as places to fatten pigs before the big November roundup and pig slaughter.
Chickens wandered around every farmstead. We now wonder if chickens might be free-range; all medieval chickens were free-range. They were used for feathers, for meat, and especially for eggs. The free-range hens would try to hide their nests, and farmers would try to find the nests before the eggs started developing into baby chicks. (Unlike modern eggs, medieval eggs would have been fertilized.) The eggs were very small by today's standards, the size of what used to be called pullet eggs.
Chickens were especially prized for their ability to keep down insects. A large part of their diet was the insects they would catch, though they would also get a little grain--as well as anything they could pick up in the farmyard. (Click here for more on chickens.)
In areas with ponds or streams, families might also have domestic ducks or geese, again raised for their feathers, their meat, and their eggs.
Cats were kept on farms to hold down the mice, but they were generally not treated as pets. Dogs, however, could be pets as well as helpful companions to the shepherds and cowherds and served as guards at night. Small dogs were bred as pets, and ladies especially might have one as a companion. Dogs, symbols of faithfulness, were often carved on late medieval tombs.