Equine Blood Type and Antibody Screen

Overview

The Hematology Laboratory at the UC Davis Weill Veterinary Medical Teaching Hospital provides blood typing and anti-erythrocyte antibody screening to support safe transfusions and breeding management in horses and mules.

These tests are most commonly used to:

Identify mares which have foals at risk for neonatal isoerythrolysis (NI)
Determine suitable donors for transfusions
Provide blood type information for breeding management, recognizing that blood typing alone cannot definitively predict compatibility between mares and stallions

Our testing methods are based on established veterinary transfusion-medicine principles developed at UC Davis and refined through decades of experience.

Submission Form and Reference Information

Pricing

Effective for samples received by June 30, 2026.

Antibody Screen - $128.00/sample*
Equine Blood Typing - $193.00/sample*

*Prices subject to change without notice. Updated 5/26/26.

Specimen requirements

For antibody screening:

Minimum of 5 mL serum (from a red-top tube).
Allow the blood to clot for at least one hour, centrifuge, and separate the serum into another plain, labeled tube.
For NI testing, if the mare has previously produced an NI foal, also submit EDTA (purple-top) whole blood from both mare and stallion.

For blood typing:

Minimum of 5 mL whole blood in EDTA (purple-top) or ACD (yellow-top) tube.
Note: International submissions must be made in ACD (yellow-top) tubes.

Storage and Shipping

Store samples refrigerated until shipment.
Ship overnight with ice packs (no direct ice contact).
Ship Monday – Thursday only, excluding holidays.
Our laboratories offer a FedEx Reduced Price Program for veterinarians.
Please do not ship USPS; mail is routed through a central campus location before delivery, delaying time-sensitive samples.
Notify the laboratory before drawing blood if submitting more than 10 samples.

Shipping Address

Clinical Laboratory Receiving
VMTH Rm 1033, Attn: Hematology
One Garrod Drive, University of California, Davis
Davis, CA 95616
Phone: (530) 752-8684

Turnaround Time & Result Reporting

Typical turnaround: 1–3 business days after sample receipt
Results are delivered by fax or email

Biological samples submitted to the VMTH Clinical Diagnostic Laboratories may be used for teaching and research purposes consistent with the mission of the University.

Background Information

Equine Blood Typing

Horses have seven red blood cell group systems: A, C, D, K, P, Q, and U. Each system contains multiple factors (antigens), and more than 30 factors have been identified.

The VMTH Hematology Laboratory currently types for A (a,b,c), Ca, Ka, P (a,b), Q (a,b,c), and Ua.

For potential donors, both blood typing and antibody screening are required to ensure safety and compatibility.

Neonatal Isoerythrolysis (NI)

NI occurs when antibodies in the mare’s colostrum destroy the foal’s red blood cells after birth.

This happens when the mare lacks a blood factor inherited by the foal from the stallion.

Testing 1–2 weeks before foaling identifies risk and allows preventive management, such as muzzling the foal and providing alternate colostrum.

Frequently Asked Questions

I want to send samples from another country. What do I need to do?
Yes — we can accept international submissions. Ship early in the week (Monday–Wednesday) to avoid weekend delays. Samples should be packed with cold packs but protected from direct contact with ice. For international shipments, blood typing samples should always be drawn in ACD (yellow-top) tubes to maintain sample stability during transit.
This mare has a negative NI antibody screen result. Now what?
A negative result means no antibodies were detected at the time of testing. Because antibody levels can change near foaling, the result is valid for only 2–3 weeks before the expected foaling date. If the mare has not foaled within that timeframe, submit a new sample for repeat testing.
Should I worry about an agglutinating antibody causing NI?
No. Agglutinating antibodies are not known to cause neonatal isoerythrolysis (NI). NI is caused by lytic antibodies, which destroy the foal's red blood cells after it ingests colostrum containing those antibodies.
While agglutinating antibodies may be detected on an antibody screen, they are generally not associated with clinical NI in foals.
If lytic antibodies are detected, we recommend muzzling the foal for 24–48 hours after birth and providing an alternate source of colostrum under veterinary supervision.
This mare has a positive NI antibody screen result. What should I do?
A positive result means antibodies were detected that could react with red blood cells.
We recommend muzzling the foal for 24–48 hours after birth and providing alternate colostrum under veterinary supervision to prevent NI.
This mare has previously had a confirmed NI foal. What should I do now?
- If the mare has produced an NI foal in the past, she should be closely managed during future pregnancies.
- If the NI was caused by anti-donkey antibodies, every subsequent foal from a donkey breeding will be affected, so an antibody screen is not necessary.
- For all other cases, submit an antibody screen 2–3 weeks before foaling to check whether antibodies are still present.
- When possible, please also submit an EDTA (purple-top) whole blood sample from the stallion for crossmatching, which can help assess compatibility and NI risk in the current pregnancy.
This mare was bred to a donkey. What now?
Mares bred to donkeys (jacks) are at increased risk of producing NI-affected foals. Perform an antibody screen 2–3 weeks before foaling to check for anti-donkey antibodies. If positive, muzzle the foal for 24–48 hours after birth and provide alternative colostrum under veterinary guidance.
I would like to test this horse to see if they could be a potential blood donor. What is needed?
Testing requires both blood typing and antibody screening. Ideal plasma donors are Aa-positive and Ca-positive with no detectable antibodies. We do not recommend whole blood donors without knowing the blood type of the recipient.
What if I am using this horse as a whole blood donor?
For first-time transfusions, donors that are Aa-positive and Ca-positive with a negative antibody screen are typically the safest.
There is no universal donor in horses; compatibility should always be confirmed before transfusion.
Before repeat transfusions, a full blood type and antibody screen of the recipient is essential.
I sent in a blood type only or antibody screen only to test for a potential donor. Can you tell me if this is a good donor?
Both tests are required to determine suitability.
If only one test was submitted, donor status cannot be confirmed until both are completed.
Do certain horse breeds have their own blood types?
No, horse breeds do not have unique blood types specific to their breed. All horses share the same seven major red blood cell groups: A, C, D, K, P, Q, and U. Each group includes multiple factors (antigens), and over 30 different blood factors have been identified.
However, the frequency of certain blood factors can vary by breed, which may influence compatibility for transfusions and breeding. Additional details on breed-related blood type frequencies can be found in our Equine Blood Typing (pdf).
What does an "unidentified antibody" mean?
An "unidentified antibody" means that an antibody was detected, but it could not be matched to a specific blood factor in our testing panel.
This may happen if the antibody targets a factor not included in the panel or if multiple antibodies are present at the same time.

Contact Information

Clinical Laboratory Receiving: (530) 752-8684
Hematology (technical questions): (530) 752-1303
Email: [email protected]

Equine Blood Type and Antibody Screen