The Smithsonian has this article up on blood antigens: <http://www.smithsonianmag.com/science-nature/your-blood-type-lot-more-complicated-you-think-180951669/> Such antigens might be the reason that usually limiting the number of blood donors (though not always possible) for a ferret is better for outcome despite only one basic blood group so far found in them. [Posted in FML 8126]