Page 765 - Veterinary Immunology, 10th Edition

VetBooks.ir animals. The prime factor influencing the duration of maternal
Similar considerations apply when vaccinating large farm

immunity is the level of antibodies in the mother's colostrum. Thus
in foals, maternal antibodies to tetanus toxin can persist for 6

months and antibodies to equine arteritis virus for as long as 8
months. Antibodies to BVDV may persist for up to 9 months in
calves. The half-lives of maternal antibodies against equine
influenza and equine arteritis virus antigens in the foal are 32 to 39

days. As in puppies, a young foal may have non-protective levels of
maternal antibodies long before it can be vaccinated. Maternal
antibodies, even at low levels, effectively block immune responses
in young foals and calves, so premature vaccination may be

ineffective. The effectiveness of vaccines increases progressively
after the first 6 months of life (Fig. 23.12). A safe rule is that calves
and foals should be vaccinated no earlier than 3 to 4 months of age
followed by one or two revaccinations at 4-week intervals. The

precise schedule will depend on the vaccine used and the species to
be vaccinated. Animals vaccinated before 6 months of age should
always be revaccinated at 6 months or after weaning to ensure
protection.

FIG. 23.12 Effectiveness to two inactivated viral vaccines in calves
between birth and 6 months of age. Clearly, early vaccination is
largely ineffective. (Data courtesy Dr. R.J. Schultz.)

Some live recombinant vaccines such as canarypox-vectored

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