Vaccination for strangles is usually only recommended when the risk for exposure by direct contact is high, like traveling to other premises and commingling with horses with high incidence of sickness, such as open public trail rides and sales. If in your case the pasture is closed to traffic of incoming, potentially sick horses, strangles vaccination is not recommended. Traffic of horses coming on your premises and your horses going out increase the risk of exposure. Strangles vaccination is not commonly recommended in horses under good pasture and stall management at home with cautious management in travel away from home. If you decide to vaccinate your horses, though, the preferred vaccine is the killed vaccine because it contains an adjuvant as published on the label. An adjuvant increases the efficacy of the bacterial antigen in the bacterin/vaccine to produce a higher immunity. The dosage is two initial doses 4 weeks apart to produce the necessary immunity with an annual or semi-annual booster to maintain the immunity. However, before starting this process, contact your veterinarian to discuss your options.