A diet containing GM soy and maize fed to rats for 30, 60, and 90 days caused a wide range of toxic effects, including DNA damage, abnormal sperm, blood changes, and damage to liver, kidney, and testes.
http://www.gmwatch.org/index.php/news/archive/2014/15834-gm-soy-and-maize-is-toxic-to-rats-new-detailed-study