West Nile Virus in Pregnant Mares

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West Nile Virus in Pregnant Mares

At this time there is no evidence that the WNV causes abortions
in mares; but there has been evidence of the virus in
the aborted fetuses. Further testing and research is ongoing
to determine the relationship between the WNV and abortion.

Vaccinating Mares and Foals

Renowned veterinarian Rob Holland, DVM, PhD, a private
practitioner in Kentucky and a technical services
veterinarian for the Intervet pharmaceutical company,
explained the protocol for vaccinating brood mares.

He recommends you vaccinate your mares four to six weeks
BEFORE foaling, what you're doing is bolstering their IgG
(a type of antibody) and all their immunological parameters.
In the case of the mare and the (unborn) foal, there's a
six-layer placenta that does a very good job of protecting
the foal against potential disease that affects
the mare, and doesn't allow any antibodies to cross it.

Maternal vs. Foal Antibodies

W. David Wilson, MS, BVMS, MRCVS, of the Department of
Medicine and Epidemiology in the School of Veterinary
Medicine at the University of California, is recommending,
based on information gathered from studies with other
vaccines, that if the mares are NOT vaccinated against WNV
or they haven't been exposed (which is now the situation
for only horses in the far western states) that foals can be
vaccinated starting at two to three months of age.

IMPORTANT NOTE: **Dr.Wilson would have serious concerns about
vaccinating foals at such a young age if their dams WERE
vaccinated or had been previously EXPOSED to WNV. Studies with
influenza, EEE, WEE, tetanus, rabies, and EHV have shown that
maternal antibody interference extends up to six months
and beyond. Therefore, many foals vaccinated at less than six
months of age fail to mount a protective immune response to
the standard two-dose primary vaccination series.

To avoid this problem, Wilson has recommended that
veterinarians delay vaccination of foals from mares which were
vaccinated or exposed to WNV until the foal is about six months
of age. Wilson recommends the following series:

FIRST vaccination at six months or older.

SECOND vaccination three to four weeks later.

THIRD vaccination six to eight weeks after the second dose
of vaccine.

What Dr. Wilson and others have found with other vaccines is
that many (foals) don't respond optimally after two doses of
vaccine even when vaccination is started after maternal
antibodies have waned. A third dose gives a little more
assurance that the ones that haven't responded to two
doses will respond to the third dose.

Please check with your veterinarian for more information on
WNV and when to vaccinate your mares and/ or foals.

** West Nile Virus Tip Sheet

Written by,
Michele D. Anderson

I am a horse enthusiast and online marketer. I specialize in horse related products and information. I own and operate two websites: Posterhorse.com and yourhorseinfo.com.

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