Answer:
Farms were not poor, it was the people who worked on the land who were poor. Each farming peasant had a small house on its own plot of land (the croft), with a larger plot behind (the toft); this was in addition to the various acres allotted to each family.
The croft and toft were used for growing herbs, fruit, additional food crops or for keeping animals. A few pigs or goats, hens, geese, a cow or two or perhaps a poor-quality horse would be the normal choices. Cows were not kept for their meat but for their milk - at the end of its productive life a cow might be slaughtered and eaten, but by then its meat would be very tough. Similarly geese and hens were primarily kept for the eggs; only when they finally stopped laying would they be eaten.
A poor family might just have a goat or two, again for milk which could be turned into cheese, which was a major element in the daily diet.
The cheapest animal to keep was a pig, since at the end of summer it could be turned out into woodland (with the landholder's permission) to feed on acorns and roots before it would be sold at market for slaughter.