Why do the hens have to surrender all their eggs?

Napoleon has made a deal with a lawyer by the name of Mr. Whymper to supply four hundred eggs a week. This is all part of a cynical ploy to convince the outside world that Animal Farm is a successful, thriving enterprise and doesn't need any assistance from humans. But of course it's all a complete sham; in reality, the farm is in serious trouble. Winter's starting to bite, and as well as a broken windmill, there are chronic food shortages, especially of grain. But Napoleon considers it much more important to keep up appearances than to prevent the loss of animal life due to starvation.
To the hens, Napoleon's deal with one of the human oppressors is a betrayal of everything Animalism stands for. They stage a rebellion, flying up to the rafters of the barn to lay their eggs. Once there, they proceed to knock their eggs to the ground on purpose, making it difficult if not impossible for them to be collected and sold. Napoleon's response is swift and brutal. He orders the hens to be deprived of their already meager food rations. Furthermore, he decrees that anyone giving food to the hens will be killed. The hens resist for five whole days before reluctantly returning to their nesting boxes.