Horses Dying of Mysterious Disease : Livestock: At least 18 animals have succumbed. And while the prime suspect is botulism, investigators aren’t yet sure.

State and local veterinary officials struggled Tuesday to isolate the cause of an unexplained ailment that has killed at least 18 horses and alarmed stable owners and equestrians throughout Southern California.

Since the puzzling malady came to light Oct. 28, it has stricken horses at riding stables in Los Angeles, Orange, Ventura and San Bernardino counties, leaving the animals with a progressive paralysis that can kill them within 48 hours.

State and local authorities were still conducting autopsies and analyzing laboratory samples Tuesday and had not yet determined the precise cause of the disease. But they said it probably is not contagious and that the most likely cause is botulism from tainted alfalfa cubes fed to horses at many Southern California stables.

The illness apparently surfaced at the Orange County Fairgrounds Equestrian Center in Costa Mesa, where seven horses have died so far. Since then, it has appeared at the Los Angeles Equestrian Center in Griffith Park as well as stables in Chino, Thousand Oaks and Chatsworth, officials said.

At some stables, stunned owners and trainers have kept round-the-clock vigils on their ailing animals, monitoring and caring for sick horses. Owners huddle in small groups, consoling each other and swapping theories on the cause.

“It’s like losing a member of the family,” said Carol Lundelius, who boards her horse at the Orange County center. As she talked earlier this week, an ailing horse in a nearby stall tried to stand but was too weak and collapsed.

“I’ve been with that horse for 24 hours,” she said. “We’ve been trying to give it water, but it’s not helping. I’m afraid it’s too late.”

Although botulism is the most likely suspect, officials said, they have not ruled out equine encephalitis, which causes swelling of the brain and spinal cord, or equine herpes.

Horses stricken with the mysterious ailment exhibit quivering muscles, shaking legs, rapid and shallow breathing, glassy eyes and sweating, officials said. The animals also may be unable to chew or swallow.

“They just become progressively weaker and weaker,” said Dr. Patrick Ryan, director of veterinary services for Los Angeles County. “They may go down and get back up, but pretty soon they can’t get back up anymore.”

He said the dying horses’ symptoms have been both “consistent and inconsistent” with botulism. While some horses have lost the ability to chew or swallow, others kept eating until their death, he said.

“We don’t have our autopsies back yet, but as soon as we do, it’ll give us a better idea,” Ryan said. The county autopsies are due back in two or three days, he said.

At a press conference Tuesday at the Orange County Fairgrounds, state veterinary officials said some of the alfalfa cubes they have tested are from Paramount Feed Co. in Paramount. The firm is one of the largest producers and distributors of horse feed in Southern California.

In one of the Paramount samples, rabbit fur and hide was discovered, which could contaminate the product, officials said.

Although officials urged horse owners to “use caution” with the company’s feed, they said they were not ordering a halt in shipments of Paramount’s products, which are used at both the Orange County and Los Angeles equestrian centers.

Paramount owner Ken Rhomberg said his firm has “changed nothing in 15 years” in the way it handles or distributes its popular feed.

“We don’t add anything to it,” he said. “I can’t believe there is a problem.”

Hay used in the cubes comes from Utah, where the company buys both ready-made cubes as well as fresh alfalfa that it compresses at its facilities in Los Angeles County, Rhomberg said.

Authorities said that the illness has not affected any of California’s six permanent horse-racing tracks.

Nonetheless, state racing officials Tuesday telefaxed notices to about 300 racehorse owners, veterinarians and state race track investigators, warning of the disease’s outbreak and saying that “so far the only common factor is cubed hay or feed supplied by Paramount Feed Co.”

Ryan said at least three horses have died at the Los Angeles Equestrian Center, where 600 horses--including Thoroughbreds, quarter horses and polo ponies--are boarded.

Christopher J. Smith, a center veterinarian, said that a “large portion” of trainers and owners at the center had switched from alfalfa cubes to hay on Sunday after word of the horse deaths spread.

“I just found out today, and I went out and bought a couple of bales of hay,” said Vicki Nicholson, who keeps two quarter horses at the center.

Times staff writers Carlos Lozano in Los Angeles and Carla Rivera in Orange County contributed to this story.