Harvest Moon: Save the Homeland

Once you have obtained a mature cow, maintain a healthy relationship with it. This can be maintained by:

1) Brush the cow.
2) Talk to the cow.
3) Milk the cow.
4) Let the cow remain outside while it's sunny.

As the love from the animal advances (which you can check through the Status on the nightstand, highlighting Cows, and then choosing the cow specifically), you will notice that the Status will say that it "Might produce Golden Milk." Any time you allow the cow outside, you will have a chance of possibly milking a bottle of golden milk from the third action. This is a vital step and make sure you gather plenty to hold on to, as many endings will require this in some way.