Once you read this article, you’ll wish you hadn’t. On that note, this is extremely graphic and will seriously bum you out. If you want the short answer to the above question, it’s “nothing good.”
In the egg industry, it’s the females that matter. Female chicks = female future chickens = future eggs = future profit. Males on the other hand aren’t of much use. The chickens generally just need to produce unfertilized eggs and don’t need to reproduce, and since the males don’t produce eggs, they basically don’t get to live long.
The only exceptions are the ones needed to grow into roosters to produce more chickens, but those are very small in number compared to the amount of those not needed.
So what happens? Any of a few things. Most commonly, they are ground up alive. Workers stand beside a conveyor belt of chicks, sorting out the males and females. The workers toss the males into the chute of a sort of grinding machine.
Right now there is a push to make egg industries include this information on the egg cartons, but it doesn’t seem to be going anywhere any time soon. Animal cruelty is pretty common in the food production industry, and this is really just the tip of the iceberg. One could even make the argument that it’s better because the chicks don’t have to suffer long. Pigs, on the other hand, often live horribly miserable lives stacked on top of each other in steel cages.