Grape seed extract is used in Wysong Pet Diets because it is a powerful antioxidant. The small amounts that we use are nontoxic.
Our pet foods have been fed to thousands of animals and people with only benefit, not detriment. Somewhere in the scientific literature can be found studies proving the toxicity of virtually every element on earth, even oxygen and water. Remember that the toxicity of anything is dose-dependent: that which is toxic at a certain dose can be beneficial at another. (See The Myth of 100% Complete and Balanced Pet Foods, and The Real Problem In Pet Feeding.)