Cows per acre
On good irrigated pasture, 2 acres should be able to handle one cow comfortably. If fertilized and maintained properly, additional animals could be added. I would recommend starting with one, then adjusting as needed. For that small of property, sheep or goats may be a better alternative as 5 of them roughly equals one cow for pasture use.
There is a person in the Pendleton area who bought two calves for his 5 irrigated acres that did not have a good pasture stand. He told me this fall that they didn't make any money on those calves because they had to feed so much hay. It is best to start small and expand if you can.
If you have further questions, please feel free to contact me at the Pendleton Extension office:. 541-278-5403.