In RL animals produce "fertilizer"; utilize this in game for all domesticated animals (except rabbits and chickens).
You would periodically (every 2-3 game days) have to shovel out your animal pens and pile up the fertilizer. Dump a wheelbarrow full near a field, CNTRL+SHFT+right click on pile (like sowing seeds) and drag a highlight over the field, your character will spread fertilizer on the field til the area is covered or the pile is depleted. Fertilizer Q will depend on the Q of the animals, their fodder, and character's farming skill; fertilizer will eventually, perhaps over course of a season, raise the Q of the soil to an average of the fertilizer Q and the default soil Q, perhaps with an area cap, and would have to be periodically reapplied or Q of soil will start dropping back to default. Neglecting to clean out the animal pens could eventually lower Q of animals in them.