Formal:
* Barn: A general term for a farm building that can house various livestock, including cows.
* Cattle shed: A more specific term for a building that houses only cattle.
* Byre: An older term for a cowshed, especially in the UK.
Informal:
* Cow barn: A simple, informal term.
* Stable: While typically used for horses, sometimes used for cows.
* Cow house: A straightforward, informal term.
The best word to use will depend on the specific situation and the tone you want to convey.