by Emily Dickson Collaborator

Failure of Passive Transfer in Foals

Failure of Passive Transfer in Foals

The word antibody is being thrown around alot these days (#COVID19), and while we are all familiar with using the word, I’m not sure we always know exactly what an antibody is and why we care so much. 

And what does an antibody have to do with our horses?

We’ve got to start with the most simple question: What is an antibody? And what is an immunoglobulin?

Immunoglobulin is just another word for antibody. And that word gives us a hint if we break the word down into “anti” + “body.” 

An antibody is a protein produced by the immune system that is designed to attach to specific antigens, or foreign substances, and remove them from the body. 

In other words, an antibody removes the bad things in our bodies that are “anti” our health. 

Antibodies, or immunoglobulins, are classified based on their structure. There are 5 main classes:

  1. Immunoglobulin G (IgG)
  2. Immunoglobulin E (IgE)
  3. Immunoglobulin M (IgM)
  4. Immunoglobulin D (IgD)
  5. Immunoglobulin A (IgA)

As horses (and humans!) are exposed to more pathogens throughout life, their immune system gets smarter and remembers the bad guys. This is how we develop immunity and the ability to produce the necessary antibodies when needed so we do not get sick upon exposure to the same pathogen. This is the whole premise behind vaccinations

What is foal failure of passive transfer?

Human babies are born with some antibodies (and immunity) that they acquired from their mom via the placenta while in the womb. These antibodies stay active for the first few weeks of life while the baby’s immune system develops and responds to the world. 

Foals do not have this luxury. Newborn foals enter the world with a functioning immune system, but no antibody protection, which means they are more vulnerable to infection in the first few weeks of life. Particularly, in the first few days, foals are completely reliant on the antibodies present in their mom’s colostrum, or first milk. 

A newborn foal has temporary specialized cells in their small intestine which are capable of absorbing the large immunoglobulins present in colostrum. These cells are especially active in the first 6-8 hours after birth. Each hour counts, as absorption completely stops (“gut closure”) at 24-36 hours of life.  

Failure of passive transfer (FPT) is what happens if the foal does not absorb high enough levels of antibodies from the mare’s colostrum. Foal FPT is thought to occur in up to 25% of newborn foals.1

How do you check a foal for colostrum intake? And what is an IgG test for foals?

An IgG test in foals tests for levels of immunoglobulin G, the antibodies consumed from colostrum. There are various antibody testing options, but one of the more common IgG tests, is the “foal snap test,” because it is an easy (just requires a blood draw), stall-side way to make sure that the foal is getting a sufficient amount of critical protection from their mama.  

Protocols on when to use the snap foal IgG test vary, but many veterinarians test around 12 hours of age, because this allows time for intervention if absorption is not going well. The general rule of thumb is that if IgG levels are below 400 mg/dL, your foal needs to be supplemented with frozen colostrum which has been thawed or a colostrum replacement.2

Talk to your vet before your foal arrives and make sure you have a plan in place for the day of foaling. Your vet is a crucial piece of this process and in setting your newborn foal up for success. 

What can a horseman do to avoid FPT in their foals?

When your foal is born, make sure to follow the 1,2,3 timeline and test your foal for IgG levels around 12 hours of life. Remember, call your veterinarian! They should be with you every step of the way when it comes to new foal care.

The first week of the foal’s life is CRITICAL, so set them up for success by protecting their immune system. 

Additionally, because foal FPT has so much to do with the mare’s ability to produce high-quality colostrum, it is important to make sure your mare is up to date on all vaccinations, in a healthy body condition, and taken care of nutritionally with the best mare and foal supplement. 


REFERENCES

1https://thehorse.com/14716/failure-of-passive-transfer-in-horses/

2http://csu-cvmbs.colostate.edu/Documents/erl-learn-foals3-failurept-apr09.pdf



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