The question is being probed by Colorado State University Professor Gordon Woods, a specialist in equine reproduction.
Woods' laboratory is part of the College of Veterinary Medicine and Biomedical Sciences.
His team is conducting research on chemistry at the cellular level to help explain why horses enjoy such a low rate of metastatic (spreading) cancer and other age-onset diseases, such as diabetes and Alzheimer's disease, in comparison to humans.
The mortality rate for horses with metastatic cancer is 8% and 0% for prostate cancer. By comparison, the mortality rate in humans is about 24%, of which 13 to 14% is for prostate cancer.
In looking at the reasons behind that difference, the Woods laboratory honed in on calcium as a regulator of cell activity. It is well established that low calcium within a cell slows cell activity and high levels of calcium within the cell speeds cell activity.
The Woods team was the first to determine, however, that horses have a low intracellular calcium level and is currently studying how to use that as a way to increase their fertility.
Studies have shown that humans with age-onset diseases have a higher level of intracellular calcium.
The next steps for Woods' team include studying the impact of increased intracellular calcium on horse fertility, and in the long term, studying the effect of reduced intracellular calcium in humans with age-onset diseases.
His research has received $US1.14 million in support in the last two years.
A total of $US1 million has come from Jess Jackson - majority owner of Curlin, 2007 and 2008 Horse of the Year.
Working with Jackson, the Rood & Riddle Equine Hospital, founded by Dr Bill Rood and Dr Tom Riddle in Lexington, Kentucky in 1986, last month contributed $US140,000 to the Woods Laboratory.
"These gifts demonstrate the strong generosity of spirit and commitment to excellence that both Mr Jackson and Drs Rood and Riddle bring to their own work and involvement in the equine industry," Woods said.
"Their investment in this programme will help take our research to the next important level in terms of understanding the biochemical causes of subfertility in stallions and cancer in humans."
Jackson said: "My family and I are proud to support DrWoods in his research. Dr Woods and his team have produced some very exciting results. We need this type of unfiltered, pure research that hopefully will lead to containment and cures of cancer and other catastrophic diseases."
Bill Rood added: "It is important for us to give back to a profession that has given so much to us. We're thrilled that we can not only help horses, but potentially advance human medicine."