Humane Society of the United States -- a pretty good source, says that "hundreds of millions" male chicks are killed annually. Here's the info:
http://www.hsus.org/farm/multimedia/...le_chicks.html
According to Mercy for Animals, male chicks are of no use to the industry because they can't lay eggs and don't grow large or quickly enough to be raised profitably for meat. That results in the killing of 200 million male chicks a year. This page includes a video of male chicks being thrown into a grinding machine while still alive. I don't recommend watching the video. Here's the page:
http://www.huffingtonpost.com/2009/0..._n_273652.html