Ask the Infectious Disease Expert

Why is Pre-Foaling Vaccination Timing so Critical?

By Duane E. Chappell, DVM

One of the most important roles we play in the health of the next generation is advising clients on the timing and necessity of pre-foaling vaccinations. While the benefits to the mare are clear, it’s crucial to remind clients that these vaccinations are just as vital for the foal’s health. Timing is the foundation of proper pre-foaling vaccination to help ensure foals are born with a strong defense against key pathogens.

THE RIGHT ANTIGENS, THE RIGHT TIME
According to AAEP guidelines, vaccinating mares 4 to 6 weeks prior to foaling stimulates production of protective antibodies, which can be transferred to the foal through colostrum. This timing is essential to maximize the amount of immunity passed on. For previously vaccinated mares, the following boosters are recommended:

• Eastern and Western equine encephalitis
• West Nile virus
• Rabies
• Tetanus
• Equine influenza virus
• Equine herpesvirus types 1 and 4

Additional at-risk vaccines may be warranted if there is a high risk of disease in your region.

THE IMPORTANCE OF COLOSTRUM AND MATERNAL ANTIBODIES
The newborn foal relies on ingestion of colostrum and absorption of these antibodies during the first 12 to 24 hours of life for protection against a wide variety of viral and bacterial diseases during the early postnatal period. An IgG test performed within the first 12 to 24 hours after their first feedings of colostrum will confirm whether the foal received adequate antibodies. Healthy foals that have nursed and absorbed adequate colostrum have an IgG concentration in their bloodstream of at least 800 mg/dL. Any foal measuring less than 400 mg/dL should receive a plasma transfusion to provide vital antibodies.

It’s important to explain to clients that maternal antibody interference from colostrum or plasma impacts when foal vaccinations are started.

WHAT  HAPPENS WHEN TIMING IS OFF?
One of the most common concerns that may arise in discussions with clients is what to do if a mare hasn’t been vaccinated or has an incomplete vaccination history. In these cases, the clock moves back. The mare will need both an initial vaccination series and a booster, which underscores the importance of initiating these conversations well ahead of foaling. You may be starting 8 to 12 weeks ahead of foaling to get a full course of vaccines on board.

Another challenging scenario involves a mare who is due to foal in just 10 to 14 days but hasn’t received her pre-foaling vaccinations. In this case, while it’s still recommended to vaccinate the mare, the foal won’t benefit from the transfer of protection from those recent vaccinations. Even if the foal passes an IgG test, the lack of proper pre-foaling vaccination timing warrants administering plasma as an added precaution.

TAKE-HOME MESSAGE
When it comes to pre-foaling vaccinations, timing truly is everything. Vaccinating mares at the right time gives foals their best chance for a healthy start. With the right guidance and early intervention, we can help clients make informed decisions that set both the mare and her foal up for success.

WANT TO ASK A QUESTION? EMAIL THE EDITOR

For more information, visit the Merck Animal Health Mare Care webpage.

Copyright © 2024 Merck & Co., Inc., Rahway, NJ, USA and its affiliates. All rights reserved.