Keep vaccinating your horses for West Nile virus

The following is the latest “Horse News and Views,” which is prepared by Dr. Bob Wright, Animal Health and Welfare, OMAFRA, in co-operation with the staff and researchers of the University of Guelph.
The monthly column highlights research topics, extension resources, reminders of common poisonings, disease, or production concerns, and coming events, and is placed on the OMAFRA website.
The number of horses identified as clinically-infected with West Nile virus (WNv) in Ontario during 2006 and 2007 was zero.
Complacency easily sets in with owners and they begin to question whether to continue vaccinating for West Nile.
A study of the West Nile virus outbreak of 2003 in Saskatchewan reports that non-vaccinated horses were 23 times more likely to develop clinical disease than those that were vaccinated.
The efficiency of the vaccine was reported to be 96 percent.
The study demonstrates that vaccination was associated with prevention of clinical disease.
The low incidence of WNv in Ontario horses probably is associated with the high level of protection to the virus that has been achieved in Ontario’s horse population, as well as that acquired by the wildbird population.
However, this virus is still present in the environment and vaccination still is highly recommended.
The sixth revised edition of Nutrient Requirements of Horses, published in
2007 by the National Research Council, is now available by fax (1-202-334-2451 or from
The list price is $99.95.
The 341 pages provide the most up-to-date summary and recommendations on equine nutrition.
A free computer program for determining the nutrient requirements of horses was developed as a companion to the book and is available at
For more information, contact Dr. Bob Wright at 1-519-846-3412 or visit

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