In the November AAEP Forum “Anthrax Affects Everyone,” (article #2859 at www.thehorse.com) the author stated that there is no anthrax vaccine licensed for use in horses. This statement is incorrect. The only available livestock anthrax spore vaccine available in the United States is labeled for use in farm animals, which includes horses. Colorado Serum Company, which manufactures this vaccine, is in the process of making the label more specific, so it will read “for use in cattle, sheep, horses, and goats.”

Michael D. Piontkowski, DVM, Director of Technical Services at Colorado Serum Company, clarified possible reactions to the vaccine. In the article, Knowles mentions that vaccinated horses might show edema around the injection site and in surrounding tissues. Piontkowski explained, “Consumer feedback and our own experience with the vaccine in horses demonstrates something slightly different. As forewarned in the package insert, this vaccine may cause a lump at the injection site, but not edema (which is characterized by the accumulation of abnormally large quantities of fluid in the spaces between cells). This lump may be up to one inch in diameter and generally subsides within two to three weeks.”

He recommends that horses be administered 0.5 mL at two sites instead of administering 1.0 mL at one site to reduce or eliminate the occurrence of an injection site lump