LEXINGTON, Ky. - Dubai Millennium, who has been in intensive care at an English veterinary hospital since undergoing two colic operations earlier this week, has been diagnosed with grass sickness.

Jocelyn Targett, a Darley Stud spokesman, confirmed Friday that the 5-year-old Dubai Millennium has the disease, which strikes about 200 British horses annually and often is fatal. It occurs in grass-fed horses, generally in the north of England and Scotland. The disease's cause is not fully known, though veterinarians believe it may originate with a toxin in spring grass. The disease's symptoms are variable but often include colic with a blockage of the colon, because it affects the digestive system's nerves. Dubai Millennium's two operations were both to relieve intestinal blockages.

Another English champion, Mister Baileys, recovered from grass sickness in the 1990's. But Mister Baileys was affected with a chronic case in his large intestine; Dubai Millennium's illness is acute and involves the small intestine, making it harder to treat. Dubai Millennium's treatment currently includes intravenous feeding, general nursing care, and medication.

"We've got a mountain to climb, but Dubai Millennium is not a normal horse and he is being given every possible veterinary assistance," John Ferguson, bloodstock advisor for Darley owner Sheikh Mohammed al-Maktoum, said in an interview Friday with Britain's Channel 4 television. "If we can keep him in a stable condition and eliminate all the toxin, we hope the healthy nerves can then start to compensate for the ones that have died. If the horse is no longer stable and is suffering then we'll have to do the right thing by him."

Sheikh Mohammed, who had flown from Dubai to England on Wednesday, returned to Dubai on business Friday.