http://www.merckvetmanual.com/mvm/index.jsp

The Merck Veterinary Manual is the single most comprehensive electronic reference for animal care information. It is brought to you as a service of Merck & Co., Inc., providing quality medical information on a not-for-profit basis for more than 100 years, and Merial Limited, dedicated to producing a wide range of pharmaceuticals and vaccines to keep livestock and pets healthy and productive.