Pigs, sheep and goats were the medium-sized domesticated animals of medieval Europe and Asia. Most meat that landed on the table was pork or mutton, most cheese came from sheep and goats, and most farmland was primarily fertilized by their droppings. In towns, their droppings were swept up and sold back to the countryfolk for gardens. Pigs, sheep and goats also had in common that they lived in herds and wandered to find food.
Pigs in the Middle Ages were smaller than modern domesticated pigs, and many of them were half-wild. They had longer legs and looked more like boars, with tusks and long snouts and wiry hair. There’s no species difference between wild hogs and domesticated pigs, and many interbred.
Interbreeding was particularly easy because pigs were not kept indoors or fenced very carefully. Swineherds walked with whole herds of pigs out to wander and find things to eat, and many pigs just fended for themselves much of the time. Wandering pigs walked through villages and towns, and sometimes they walked into houses whose doors were open for daylight. Since they were often half-wild, they were known to harm children. Babies were occasionally killed in their cradles when the mother had gone out for a few minutes and a pig came in.
What made pigs the ideal farm staple was that they would eat anything. In towns, they ate garbage, probably including offal from butchering or tanning. Early medieval Europe was heavily forested; pigs could eat roots and nuts. In fact, during the technological revolution in iron production, vast acres of established oak forests were cut down and turned into charcoal, and this hurt the pig population. Late medieval farmers had to think harder about what to feed their pigs, and eventually pigs were kept in pens. Brewing ale created a sloppy mess of grain that had to be strained out, which was an ideal pig food.
Sheep, too, were smaller than modern ones. In cold Northern Europe, their wool was their most valuable attribute, but they were also kept for milk. Sheep were more likely to be milked than cows, in many parts of medieval Europe; there were far more of them in most places. Sheep could find food at high altitudes where grain couldn’t grow.
Selective breeding of sheep went on all through the medieval years. They could be bred for wool, meat, or milk. Additionally, in the Middle East and Central Asia, sheep were bred for fat tails; their stored fat in the tail became a major source of cooking oil. In Northern Europe, Cistercian monasteries worked on sheep breeding, just as they made scientific progress in iron smelting and winemaking.
In Spain, breeders created fine Merino wool with sheep who could live on a sparse diet and walk long distances. The back country of Spain was criss-crossed with migration trails, as shepherds moved the Merino sheep from water source to water source. Partly due to their isolated herds, long walks, and necessary cooperation to maintain the trails, breeders in Spain could do more controlled experiments. After Merino wool came on the market, post-medieval sheep were interbred with Merinos, so the old multi-purpose sheep breeds are basically extinct. As wool improved, the wool trade increased and so did the herds of sheep. There were far more sheep by the end of the Middle Ages.
Goats tended to be kept farther south, in the Mediterranean region, but also in higher elevations. Goats, like pigs, will eat almost anything, so they can sustain themselves on dry, scruffy plants. On the other hand, by eating everything, goats also contribute to turning land into desert. A small herd of goats can drastically change the landscape in a year or two; the only things that grow are the few plants they don’t eat. Goats, too, were bred for meat, milk, and wool. During the medieval period, breeders in the Anatolian Plateau (modern Turkiye) developed Angora goats that looked a lot like sheep, and whose wool rivaled even that of Merino sheep.