The people who hunted the sparse desert animals responded to drought by managing the wild resources they hunted and gathered, especially wild oxen, which had to have regular water supplies to survive.

As he cannot pump enough water out of the well, irrigation for his cornfield has become impossible and he's faced with losing his flock of 100 sheep and 20 oxen because of lack of fodder.

So when the brothers came home thirsty, they found twelve bowels filled with water. They pitched in and drank, and instantly changed into a herd of oxen.