Source: http://www.animalsaustralia.org/features/egg-industry-secrets.php
This report is from Australia, and may be relevant to us as well. In any case, “cage eggs” is a cruel industry as poultry hens are subjected to much suffering and harsh treatment in farms worldwide.
Buy only free-range unfertilised eggs! You may pay a bit more, but you sleep easier at night knowing that the eggs you eat do not comes from a cruel industry.