There are many animals in the land which, with sufficiently high farming abilities, can be nurtured and looked-after such that they remain loyal to a certain locale - a meadow, rich with grassland - and, in addition, sympathetic to the individual responsible for bringing them to such a bountiful place. The animals will then allow themselves to be shepherded, to be coaxed into lovemaking, to breed and thus a herd or flock may grow. There are numerous advantages to owning a goodly number of animals: from the sheer joy of farming to the more utilitarian purposes (commodities like leather, wool, and meat; mounts for cavalry legions; milk from cows, etc).
Animals of the livestock variety (cows, bulls, horses, sheep, etc) will require regular feed. This is achieved in the background when they are housed in a suitably lush meadow - though you must ensure the meadow is not overpopulated else it may be depleted beyond the point of springtime regrowth. When a meadow becomes devoid of food the livestock will slowly starve. When starvation reaches a sufficiently dire stage the animal will flee, searching wildly in an ever-increasing circle for anything to sustain itself. It may damage other crops if it stumbles upon fields planted with anything it would find edible. It will, if it endures bouts of starvation, be much retarded when it comes to breeding and future trust.
There are two items a farmer may have fashioned to aid in the feeding of livestock: the trough and the manger. The former is generally used outside and can take the place of grassland meadows (or indeed any other naturally growing foods) so long as it remains stocked up with straw or hay. The manger tends to be used indoors, like in stables, and is also filled with straw or hay. The amount of food a trough and, even more so, a manger can hold is limited and nothing like the extensive bounty found in a lush meadow so they tend to used for smaller herds or little groups of prized animals (e..g. one's favourite steeds in a safe stable).
Firsthand experience is the best tutor when learning the nuances of farming: tending the grassland meadows, nurturing livestock, encouraging their breeding, aiding in birthing, expanding a herd or flock, seeking out fresh meadows during difficult times of the year... a whole world of exploration for one so inclined.
