How many vaccinations should mares have whail pregnant?

The exact answer is going to depend on what area of the world the mare is in. In the United States, a mare should be current on the vaccines which the American Association of Equine Practioners considers to be "core vaccinations" during pregnancy: Eastern and Western Equine Encephalytis, West Nile Virus, Tetanus and Rabies. It is also recommended that they be vaccinated against Equine Herpes Virus at 3, 5, 7 and 9 months of gestation as this virus can cause abortions. Vaccination against Influenza, Strangles and other possible infectious disease may also be recommended based upon the risks to the specific mare. Boostering for these diseases is also recommended about 1 month prior to foaling to help ensure the highest level of maternal antibodies get transferred to the foal through the colostrum. For vaccination recommendations for each specific situation, horse owners should contact their veterinarian prior to breeding their mare as there may be increased risk of contracting infectious disease during the actual breeding.