PubMed
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=search&DB=pubmed
Although this resource is mostly for human medicine, there are many articles that relate to equine health. There is some full text available.
USDA
United States Department of Agriculture
http://www.usda.gov/wps/portal/usdahome
Includes information about animal health and animal production.
AGNIC
http://www.agnic.org/
AGNIC is a distributed network that provides access to selected agriculture-related information, subject area experts, and other resources. It was established by an alliance of the National Agricultural Library, land-grant universities, and other organizations committed to facilitating public access to agricultural and related information. This site is being created by a team of librarians at the Texas A&M University Libraries at Texas A&M University in College Station, Texas.
Horse Genetics
University of California at Davis
http://www.vgl.ucdavis.edu/~lvmillon/
Contains information on horse genetics, gene mapping and horse typing.
HorseQuest
http://www.horsequest.info
HorseQuest.info contains answers to questions in the subject areas of nutrition/feeding, health, breeding, parasites, training, marketing, diseases, facilities, horsemanship and management just to name a few. Provides reliable and up-to-date horse information through a knowledge base of commonly asked questions that have science-based, peer reviewed answers.
International Museum of the Horse
http://www.imh.org/imh/imhmain.html
An extensive list of equine related links under 'Links to other sites,' including a comprehensive look at ninety five equestrian breeds from around the world.
Livestock Virtual Library
http://www.ansi.okstate.edu/library/
Links to information about breeds and selection, general care, nutrition and feeding, and more.
Oregon State University's Equine Science
http://oregonstate.edu/dept/animal-sciences/horse/index.html
OSU's Equine Science home page. In particular, check out the 'Favorite Links' page with links to breed websites and more.
University of Kentucky horse publications
http://www.uky.edu./Agriculture/AnimalSciences/farm/equinepub.html
Equine publications concerning nutrition, management, breeding, and more.
University of Missouri Cooperative Extension Horse and Mule Publications
http://muextension.missouri.edu/xplor/agguides/ansci/horses.htm
Equine publications concerning nutrition, health and disease, and occasional articles pertaining to breeding.
Veterinary Genetics Laboratory
http://www.vgl.ucdavis.edu/
Parentage testing, coat color, and other research as a part of the School of Veterinary Medicine, University of California, Davis. There is an extensive links page.
VetGate
http://vetgate.ac.uk/
VetGate is a gateway to evaluated, quality Internet resources in animal health, aimed at students, researchers, academics and practitioners in animal health. Created by librarians and subject experts at the University of Nottingham Greenfield Medical Library in the United Kingdom.
EquiSearch.com
http://www.equisearch.com/
EquiSearch is an online center for the equine community, featuring horse sports and industry news, horse care information, training techniques, products & services geared to horse enthusiasts and a forum for dialogue among active horse people
Equiworld
http://www.equiworld.net/
Equine-related information about horse care, health, breeds, evolution, and more.
TheHorse.com
http://www.thehorse.com/
The Horse provides health information for horses of all breeds. It is not a journal of record to report research findings. Instead, it is a magazine that features practical articles that are edited to interpret complex issues. It is free to use, but you must register before you search.
HorseIllustrated.com
http://www.horseillustrated.com/horse/
Links to information about horse management, riding, training, and more.
Western Horseman
http://www.westernhorseman.com/
Information about horse care, horsemanship, tack, and more.
Breeds of Livestock
http://www.ansi.okstate.edu/breeds/horses/
Horse Breeds of the World
http://www.imh.org/imh/bw/home2.html
American Association of Owners and Breeders of Peruvian Paso Horses
http://www.aaobpph.org/
American Donkey and Mule Society
http://www.donkeys.com/ADMS.html
American Holsteiner Horse Association
http://www.holsteiner.com/
American Indian Horse Registry
http://www.mediadesign.net/indianhorse/home.htm
American Miniature Horse Association
http://www.minihorses.com/amha/
American Morgan Horse Association
http://www.morganhorse.com/
American Quarter Horse Association
http://www.aqha.com/
American Shire Horse Association
http://www.shirehorse.org/
American Trail Horse Association
http://www.trailhorse.com/
Arabian Horse Registry
http://www.arabianhorses.org/default2.asp
The British Horse Society
http://www.bhs.org.uk/Content/Default.asp
A British charitable society that promotes knowledge about, and use of, horses and ponies.
Gaited Horses.net
http://www.gaitedhorses.net/
International Andalusian Lusitano Horse Association
http://00443c3.netsolhost.com/new/default.php
The International Morab Breeders' Association
http://www.morab.com/
National Reining Horse Association
http://www.nrha.com/
Irish Draught Horse Society
http://www.irishdraught.ie/index.asp
The Jockey Club
http://home.jockeyclub.com/
National Snaffle Bit Association
http://www.nsba.com/net/index.asp
National Spanish Horse Association
http://www.horsetalk.co.nz/spanishhorses/spanish.shtml
United States Trotting Association
http://www.ustrotting.com/
World Arabian Horse Organizations
http://www.waho.org/