Selenium distribution US map (plus other mineral data from USGS):
http://tin.er.usgs.gov/geochem/doc/averages/se/usa.html

American Association of Equine Professionals home page:
http://www.aaep.org/

American Association of Equine Veterinary Technicians and Assistants:
http://www.aaevt.org/

List of multiple Veterinary associations:
http://www.vspn.org/library/wwwdirectory/Organizations.htm

American Veterinary Chiropractic Association:
http://www.animalchiropractic.org/

American Veterinary Medical Association:
https://www.avma.org/Pages/home.aspx

FDA CVM:
http://www.fda.gov/AnimalVeterinary/

Finish Line Horse Product, Inc:
http://www.finishlinehorse.com/

National Animal Supplement Council:
http://www.nasc.cc/

VAERS (vaccine adverse event reporting system):
http://www.fda.gov/BiologicsBloodVaccines/SafetyAvailability/ReportaProblem/VaccineAdverseEvents/QuestionsabouttheVaccineAdverseEventReportingSystemVAERS/

Journal of Equine Veterinary Science:
http://www.j-evs.com/

International Association of Equine Dentistry:
http://www.iaedonline.com/

Equine Podiatry Association (UK):
http://www.epauk.org/

Sciencedirect (source of Equine medical textbooks)
http://www.sciencedirect.com

List of multiple Equine associations:
http://www.theequinest.com/horse-equine-organizations/

Finish Line Horse Product, Inc:
http://www.finishlinehorse.com/