These are garden sheds that have been converted into cow barns.
They’re small but useful.

Small cow barn:
Category: Animal Pens
Price: $8,500
Daily upkeep:25$
Capacity: 6 cows

Old but larger barn:
Category: Animal Pens
Price: $12,000
Daily upkeep:25$
Capacity: 6 cows

I’ve equipped both barns with manure pits that you can easily scoop out with a shovel.
Plus, milk and slurry are included!