8 Animals do it for me all the time. (at least 3 cows but 8 animals that drop milk ) I have 3 and one in inventory. If yoou are maxout in animals, they go to your inventory.

Just got my first highland. I noticed that milk drops collected after yogurt maker was full were lost, so I checked that I only needed 4 more drops, I fed each goat one at a time as soon as it was full, not one drop more I collected the yogurt and collected an ultra rare yogurt. I did it the next time and now I have my cow, or rather "coo"

buy swiss cow at least 4,and harvest them at the same time,i already have10 highland cows...lol

Ir took me a long time to get the ultra rares. I made sure I had a good variety of cows and goats. I am working on my 2nd Hightland Cow and got the ultras right off the bat! Keep on keepin on!!!

The only secret is patience. It's called Ultra Rare for a reason.