How do the pigs gain the rights to the cow's milk?

In Chapter Two, three cows interrupt Snowball's speech by lowing in pain, since their udders are full to bursting. Some pigs milk the cows, producing “five buckets of frothing creamy milk” (44). The animals wonder what to do with the milk, but Napoleon puts off that decision for a later time. The animals begin the harvest in the fields, and when they return the milk is gone. The pigs have taken the milk for themselves.