Enterolab sent me an email response today:

"We do know that the gluten protein is not passed through to the cow's milk. The gluten is broken down during the digestive process to the point that is passed on as waste. We do not know if grain vs grass could have an affect on the chemical make up of the casein protein. As far as we know there have been no studies on this particular subject. Thank you, Kathy Carreon EnteroLab Customer Service"