I would like to nominate One Horse at A Time (OHAAT). Not only do they supply $ for emergency food and medical care but they supply money for and encourage gelding stallions to help them become more adoptable and to prevent accidental and over-breeding. The info below is from their website:
One Horse at a Time, Inc. or "OHAAT" differs from traditional rescues in that we offer financial support for emergency hay, feed and vet care, not just to 501 (c) 3 rescues but also to private owners in need. However, the assistance program we're most proud of is our gelding grant program. OHAAT believes that one of the leading problems facing the equine population is overbreeding. Unlike most gelding programs available, OHAAT provides funds upfront to help pay for gelding. The help horses of all sizes and breeds but have a very soft spot for off track thoroughbreds who are thrown away like trash when they can no longer run.
Through our unique program, OHAAT is able to help horses all across the United States and has even helped horses in Canada. We feel our program reaches further and deeper into the issue of displaced, abused and neglected horses through our ability to spread funds across the nation to numerous rescues and individuals in need. Your donations are tax deductible. We do the research and footwork for you. Our grant recipients go through a reference checking process and we only pay the service providers.