What's the Scoop: Blood Type & Horses

What’s the Scoop?

Blood type and Horses

I have always been vaguely interested in equine genetics of all different sorts.  I have a more than basic understanding of equine color genetics and am always fascinated about the newest testing coming out for various inherited equine genetic disorders.  From this general line of thought, I started looking into equine blood types.  I understand human blood typing as I have worked as a blood banker, but horses are an entirely different situation!

I decided to do a friendly little post with some of the basic overviews in case anyone else out there enjoys a good read!

From my general research there are seven accepted red blood cell systems A, C, D, K, P, Q, and U.  It also appears that there may be an 8^th system that is not universally accepted yet.

Within each system, are multiple antigenic sites known as factors.  Think of the A, C, D, K, P, Q, and U as houses and the factors are different rooms within the house.  The factors are listed in parentheses after the systems so it ends up looking like this: A (a,b,c), Ca, Ka, P (a,b), Q (a,b,c), and Ua. 

The most common blood type for a horse is Aa Ca+.  Here is a fun chart taken from UC Davis with the breakdown between breeds and blood type.




So it looks like the breeds most commonly being AaCa+ include Thoroughbreds and Arabians.  How fun!

Humans naturally form antibodies to other blood types so a blood type and antibody screen is imperative before attempting a transfusion.  There is of course, the universal donor type (O negative), which is compatible as it has a lack of antigens more than anything else.  However, horses apparently don’t naturally develop antibodies to other blood types, so usually the first blood transfusion, even if with a different blood type isn’t of consequence.  The exception of this are broodmares that may have been sensitized from previous pregnancies.

Some people may have heard of women having issues with their pregnancy from different blood types.  Rhogam is a product commonly issued to RH negative women who have RH positive babies.  Humans are a little bit different than horses in that RH antibodies (as well as others!) generated by the mother against her child can cross the placental barrier and can cause Hemolytic Disease of the Newborn. 

In horses, this is a little bit different in the fact that while a mare may in fact have antibodies against her foal’s red blood cells, until that foal actually ingests colostrum containing these antibodies, they are generally healthy and safe.  Neonatal isoerythrolysis is what develops if this foal would consume colostrum containing these antibodies.  This results in anemia, jaundice, destruction of red cells, increased heart rate and all around bad things.  This is somewhat more common in certain breeds, including Friesians.  It is also common in mare to donkey breedings. 

The likelihood of this disease can be screened for by taking blood samples from both the sire and dam.  If likely, the foal should be muzzled after birth. 

So if anyone else is a happy nerd, hope you enjoyed this scoop and just look at your horse and marvel at how many potential blood types they have!