These were sold by Kenner starting in 1977. You would get Milky to drink from a trough of water by pumping its tail. I’ve never worked on a farm, but I doubt that is the method used for real cows. After that, you could milk Milky into a tiny bucket. It may seem udderly ridiculous, but it was sold for a while before Kenner mooved on. If the toy was a marketing failure, we can forgive them. To err is human, but to forgive is bovine.

The 1977 TV commercial is a thing to behold.

Milky in the flesh, as it were:

Milky

If that doesn’t satisfy your farm themed toy itch, see also Gobbles the Crazy Eating Goat.