neonatal isoerythrolysis in foals

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Well-Known Member
Dec 12, 2002
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Balfour, North Dakota
I recently had a foal that was born and seemed completely normal. After a couple of days, she started going downhill. I took her to the vet and he did blood tests and also the test to see if she got enough colostrum. The vet said it came back that she had gotten adequate colostrum and we waited on the blood test. When that came back everything pointed to neonatal isoerythrolysis. (kind of like RH factor in people) The mare had developed antibodies to the stallions anitgens and was then producing colostrum that would basically attack her filly's red blood cells. I took her home and fed her every two hours as I had been doing. She was not doing well and back to the vet we went. It was too late. We did all that we could do and we lost her.

I have since been trying to warp my brain around this. I own 3 mares that are all sired by the same stallion.

1. Lady

2. Jewell

3. Feather

Not only are they half sisters, but Jewell and Feather are full sisters. Once I started reading, all I could think of was my mares need to be blood typed. So, last Monday I took all three mares and my two stallions Flash and Knight in for blood draw to be sent off to UC Davis for blood typing. I just got a call from my vet yesterday that the results came back "incompatable" between Flash and all three mares.

However, Knight can be bred to Jewell and Feather with no issues. My vet apologized and said she didn't have time to look at each blood type to be able to go into a detailed explanation at the moment and would call me back some other time. I know they are busy right now with cattle and their fair share of C-sections.

So, if NI is like the RH factor in people, Does that mean that my mare Lady and my stallion Flash have the same blood group but one is positive and one is negative? This is my assumption.

Which would then mean that Flash is also a problem blood type? Flash has sired 22 foals previously if I look up his progeny in the AMHR studbook. I had no idea as all previous foals were happy and healthy and I had no reason to think there was a problem.

I am now in a panic as I also bred Feather to Flash and I am unsure if she is in fact pregnant. I know, I should be able to tell, but she is a maiden and it gets cold throughout our winters (we had exceptionally cold days that averaged -20 for long periods of time) so I feed "plenty" of hay. She has a belly that's for sure. So now, I have an appointment to take Feather in on Monday and have her blood drawn and plan to sent that in to either confirm weather she is in foal or open. I don't think I have ever prayed so hard that a mare will be "open".

The surprising fact I have been reading is that the first foal is "usually" not affected. This would explain why last year Jewell had a sorrel colt sired by Flash and he is fine. This would have been Lady's first foal and yet we lost her. It makes me wonder if in fact when I bred her the previous year if she "took" but absorbed the foal and in doing so was exposed to the stallions blood antigens that way so that this foal would have technically been her second?

My question is this: Has anyone else every dealt with this? How common is it? I am thinking that Flash needs to be gelded and taken out of the breeding pool? The daughters he has sired could possibly have the same issues? His son will be gelded as soon as he drops. Since Lady cannot be bred to Flash or Knight, she is also one that should just NOT be bred? So many questions.....if anyone has any experience with this I would love to hear from you. I am still trying to figure this out so I do the right thing. I would NEVER purposefully sell a stallion that would pose a problem for someone else and cause them the heartache I went through.

Here is a link to pictures of the mare and stallion that produced the NI foal.


Unfortunately we have dealt with this. It is a good news/ bad news situation for you. The bad news is the sire and dam are incompatible and you are going to have a problem IF she is in foal. The good news is you know in advance and you CAN save the foal. It will take work but it can be done. When the foal is born it will need to be muzzled so it can NOT nurse it's momma's colostrum. She will need to be milked to remove her colostrum. The baby will therefore need to be bottle fed a colostrum from another source(ask your vet). After a few days of milking and bottle feeding the baby can then nurse from Mom.

The problem lies not with the stallion but with the mare. Your mares have antibodies against the stallions blood group. ANY stallion with that blood group. Somewhere along the road an injury has happened so that the blood groups mingled in the mare. Normally the placenta forms a barrier between mother and baby. So even if you breed 2 incompatible horses together the baby will fine, as far as NI is concerned, until it is born. Then when the antibodies are passed to the foal with the colostrum all heck breaks loose. And it will get faster each time the 2 are bred together.
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I have already purchased the EZ Milker and have that ready and waiting so the mare can be milked and stripped of the colostrum. I have talked to my vet about looking for a source for colostrum. I have been looking online and have mostly found colostrum supplements and only one source for actual colostrum witch at last check only had 3 pints in stock. We are also looking at a plasma transfusion in case at the time of foaling we cannot get our hands on colostrum.

I wish my vet would have been able to tell me what blood group my mares were and what group my stallion Flash is. I will NEVER breed him to them again now that I know about this.

The one thing I question is that Jewell and Feather CAN be bred to Knight safely, but Lady CANNOT. Until I know which blood groups they are from the results, I guess I am just grasping at straws.
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There is also a simple test that can be done at home at the time of foaling. You can do this just to be sure, on every single foal born. I have never personally done this myself, but it is said that you mix a few drops of blood from the placenta with milk/colostrum from the mare. If it stays mixed, you are safe, if it separates, you need to muzzle the foal for a couple of days and find an alternate source of colostrum. This condition does not mean the foal can never nurse from it's dam, it's just the colostrum that is the deadly issue. Once the milk comes in (after 2 or 3 days), all is safe, baby can nurse, and life goes on as normal again. Is best to muzzle baby, and keep it with it's dam, and strip colostrum several times a day to ensure it leaves her. Here is a foal muzzle that I made once when I ran into this problem with a new foal here. I cut the top off of a pop bottle and left it long enough at the other end so foal could not nurse. I cut the bottom out so lots of fresh air etc. but so that she could not nurse.


Michelle, no need to feel stupid! Raising animals is a constant learning process. You can easily use a 60cc syringe to strip mares too. If you visit the info pages here on LB you'll find them to be a real wealth of information, and instructions on making the syringe milker are on there too. Is easy to make, and works great!

And while on this topic, it might be worth mentioning that each year, you should collect and save colostrum from each mare that foals. Freeze it in one or two ounce packets. Some people freeze it in ice cube trays. It will keep for up to 2 years. Make sure you date it on the package, and name which mare it came from. Collecting from every mare that foals will give you a supply to keep on hand for use such as this. It will not run the mare short for the foal she is nursing if you collect it from her a few times within the first 12 hours or so.

NEVER unthaw/defrost in a microwave as it kills all the good from it, and it will be worthless!!
Just because Lady cannot be bred to your stallions (unless you do as described above and make sure that the resulting foal does not get any colostrum from lady) does not mean there is any danger in breeding Lady's sisters (half or full sisters) to either stallion. As said--the problem is not with the stallion. The problem is not the incompatible blood types--that is a problem only in sensitized mares--a mare may be sensitized by her foal if some placental disease allows the passage of blood from foal to dam. A mare may also be sensitized by a blood transfusion of incompatible blood, or by the use of a vaccine that contains horse erythrocytes (and I do not know which vaccines might contain those!). Once she is sensitized, her body creates antibodies to the incompatible blood type, and those antibodies are concentrated in her colostrum. If the mare has not been sensitized--she can be bred even to a stallion with an incompatible blood type and the resulting foal will be perfectly normal.

So--even though Lady has been sensitized, it is unlikely that her sisters have been; I have never heard of this being a familial problem, it is just something that happens to random mares. Odds are in your favor that Jewell and Feather are perfectly fine to breed to any stallion you choose, regardless of blood type. To be 100% sure, you can do as mentioned, and "test" the colostrum by mixing a small amount of it with a few drops of the placenta blood--then you know immediately if the foal is safe from NI.

With a mare that you know is sensitized--you can breed her to a stallion with a compatible blood type, and then there will be no problem with the foal being killed by the mare's antibodies to a different blood type. It isn't that one specific stallion that is the problem--it is any stallion with the wrong blood type. If the mare does get in foal to an incompatible stallion--it's important that the foaling be attended, so that the foal can be prevented from nursing until the colostrum is gone. An affected foal CAN be saved with large volume transfusions of whole blood within 24-48 hours--I know people who have saved foals this way.

When my vet called with the results, she told me that NONE of my three mares can be bred to Flash. They all came back incompatible to breed with Flash. That is one reason I am still trying to understand this. He has to be part of this?

I tested all 3 mares and my 2 stallions thinking it was overkill and that I would find out it was Just Lady. But, I am so glad I tested everyone because now I know Lady cannot be bred to Flash OR Knight, and Jewell and Feather can ONLY be bred to Knight.

I stopped in to the vet this afternoon to pick up the copy of the lab results. The vet was helping people with cattle and the receptionist got me the papers. It wasn't until I got home I realized that the papers she gave me were the ones we had submitted of my horses and not the actual faxed results......

On another note, people rarely blood type anymore since we have gone to DNA. How would I ever find a stallion that would be "safe" to breed her?

It may be that your vet is suggesting not to breed any mare except to a stallion with compatible blood type--just to be extra cautious--just in case another mare does get sensitized. It could happen but the condition is are enough that i wouldn't expect that it would. NI is a mare problem not a stallion problem. Otherwise--perhaps your vet is not fully aware of how NI works? NI is strictly a problem with the mare and the antibodies she produces. I just had a look around the 'net to see if there is new information I am aware of, and there is not:

To bloodtype you would have to have it done specifically for the purpose of determining compatibility with the problem mare. Otherwise--the one article above gives good information on serum testing the mare prior to foaling.
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I think maybe there is reason, since 2 of the 3 mares are full sisters and one is 1/2.
Lady cannot be bred to Flash or Knight. They have blood incompatibility. Luckily however, Jewell and Feather can safely be bred to Knight.
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