Cato The Elder (In On Agriculture 10-11) suggests the requirements for running a 150 acre orchard includes thirteen workers, one of whom being a swineherd, another a shepherd. For a sixty acre vineyard, he suggests sixteen workers, including one swineherd, and a willow worker (Secondary question, what is a willow worker?), and no shepherds.
Orchards and vineyards are not pigfarms, so why does he suggest swineherds and a shepherd?
The answer is in the text itself. i will try to explain:
Salix, or osier or willow, was a natural binding/joining/tying material, also used to make baskets. In sections 10 and onwards, Cato says you'll need baskets for manure, wine-lees, planting, pressing (not sure if this is an oil press or a wine press), and other. "Let ripe withes and willow branches be gathered betimes as material for making new baskets and mending old ones"
As the hand-woven baskets get heavy use, especially for transporting bulk materials on pack animals, a full-time willow-worker for basket maintenace is necessary.
(edit: animals that carry heavy packs, not animals that run in packs)
In section one, Cato recommends that if the first two choices of vineyard or watered garden are not practical, the third-best type of farm to have is an osier-bed, tertio salictum.
Cato writes to cultivate willows if there are riparian or wetland soils available, in section 6. https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Cato/De_Agricultura/A*.html#6
Plant Greek willows along the border of the thicket, so that you may have withes for tying up vines.
[Salicem Graecam circum harundinetum serito, uti sieto qui vineam alliges.]
As for the livestock, it was a good idea to have onsite animals to provide fertilizer. You would not go to Home Depot to buy a 40-lb bag of steer manure in Cato's day; the idea is for the farm to provide for its own needs rather than purchasing, then hauling, great quantities of willow saplings or animal poop regularly. I do mean great quantities: Cato devotes attention in several sections of his book to management of soil and manure; after all, without rich soil, your farm is going to fail. In any case, if you are to have livestock, you will therefore need someone to watch the livestock, hence swineherds and shepherds.
In section 7, Cato says to use pig manure as fertilizer on the roots of fruit trees.
(eo lotium suillum aut stercus ad radicem addere oportet, uti pabulum malorum fiat)
and In section 10, "3 pack-asses to carry manure".