A horse's hoof is not a single, solid body part. It's a complex combination of parts, an evolutionary marvel that allows a half-ton animal to run at tremendous speeds on the tips of its toes.
But when a horse develops laminitis, an inflamation of the tissue that bonds the horse's bone to the inner wall of the hoof, the hoof doesn't work properly, the animal is in pain and its health can be severely compromised.
That's what Barbaro is up against, and why his doctors say his prognosis is "poor." No lesser horse than the great Secretariat, the 1973 Triple Crown winner, was felled by laminitis. He was euthanized because of it in 1989.
Laminitis, or founder as it's also called, has multiple causes, and scientists still are debating exactly what prompts the disease, said Rob Sigafoos, a horse expert at the University of Pennsylvania. In Barbaro's case, it's blamed on the uneven weight distribution between the rear legs after the injury to the right hind leg in the Preakness Stakes.
Specifically, laminitis is an inflamation of the sensitive laminae -- the sensitive tissue beneath the hoof wall that contains nerves and vessels. Laminitis can develop rapidly and is life-threatening, although it is treatable. In mild cases, horses can recover and resume some athletic activity, according to Lexington, Ky.-based American Association of Equine Practitioners.
Dr. Dean Richardson, the chief surgeon who has been treating Barbaro, described the problem this way at his news conference on Thursday:
"A horse walks on the tip of its middle digit, OK? Evolutionarily speaking, they adapted to walk on the tip of their middle digit. ... So, they're essentially walking on the nail of their middle finger. And if really what you're talking about is the bone inside of the hoof has to be attached to that nail ... what's called the keratinized tissue, the hard tissue of the hoof.
"The bone is attached to that by tissue called lamina. They are inter-digitating pieces of tissue ... basically the inanimate tissue goes to the animate tissue, if you want to look at it that way.
"That tissue, if it becomes damaged, which is what happens in laminitis, separates, and then you lose the connection between the bone and the hoof. And if the horse loses the connection between the bone and the hoof, it's exquisitely painful to the horse because the horse needs that connection to walk around.
"... The only way you can cure it once it's at this point is many, many months of the horse actually growing a new hoof wall that extends down from the top, just the way you would regrow a nail if you had your nail essentially pulled out, which I think everyone recognizes to be very painful."
"So, it is, it's a painful condition. It's a serious condition. And it's a very difficult, long-standing problem to deal with."
The disease also is seen in horses with systemic infections and mares that retain the placenta. Diet also has been implicated. When the condition strikes their front feet, horses can be seen trying to shift their weight to their back feet.
Laminitis is treatable with drugs and special horse shoes, especially in mild cases. One recent study, a survey of United States horse operations other than racetracks with at least three horses, found that about 13 percent of them had at least one laminitis case in the previous year.
The Asociated Press and the National Thoroughbred Racing Association contributed to this report.