TRABUCO CANYON – Dog attacks aren’t unusual in Orange County – last year alone, 266 canines were declared dangerous and vicious by OC Animal Care.

But attacks on horses are less common, with just seven since 2012.

County officials say three rare Icelandic horses and their riders were attacked at O’Neill Regional Wilderness Park on Friday.

Jennifer Hawkins, interim director at OC Animal Care, the county’s animal care agency that oversees 17 cities and the unincorporated areas, needs the public’s help to find the owner of the brown and white dog that attacked the group in an area of the park where dogs are not allowed. Hawkins said the agency will investigate the case.

If identified, the dog will be investigated as dangerous or vicious.

Owners who are allowed to keep a dog that has been declared dangerous or vicious face restrictions.

Such dogs must live in locked runs and wear muzzles when being walked. Owners also pay hundreds of dollars in permits, must post a “Beware of Dog” sign at their home and are subject to regular unannounced visits by county or city animal control officers. OC Animal Care requires owners to have $100,000 liability insurance. Some city agencies require higher policies.

Since 2012, there have been seven dog versus horse incidents reported to OC Animal Care, Hawkins said. Thousands of riders use county parks each year.

Helga Thordarson, who’s ridden county trails for 25 years, said she has experienced heel-biting dogs a few times but never a full-on attack.

Thordarson says she photographed a group who was with the dog. O’Neill park rangers searched for the group unsuccessfully. Thordarson has posted a photo of the group with the dog on Facebook.

“We need to find out if that dog has a history of bites in its past,” County Supervisor Todd Spitzer said Monday. “If it has a history, it needs to be impounded.”

Friday’s attack left two of the three horses wounded and put rider Sandie Weaver of San Juan Capistrano in the hospital. Veterinarians also aren’t sure whether injuries to the horses could be life-threatening.

“There are vital structures on horse legs that can be damaged,” said Paul Wan, an equine veterinarian at Equine Veterinary Specialists in Norco. “Sometimes we have to put those horses down because they become lame.”

Wan said in his 20 years, dog attacks generally are on horses confined in stalls, paddocks or pastures.

Weaver, who rides Oska, a 22-year-old mare, was with Thordarson, riding Tyr, a 15-year-old gelding, and Linda Knight, on Diana, a 16-year-old mare, for their regular ride at O’Neill park, Thordarson said. They were headed down from the top of Live Oak Trail.

Once they hit Coyote Trail, the dog went past the horses, but then charged from behind, launching at Oska’s throat, Thordarson said. Weaver used her crop to whip it away.

Thordarson jumped off Tyr and tried to beat the dog off Oska, who had spun around. As the horse turned, Weaver fell off, Thordarson said. Knight’s horse followed Oska back up to the top of Live Oak Trail, Thordarson said.

Tyr spun around and kicked out at the dog, Thordarson said.

“It was me holding the reins, the dog in the middle and the horse on the other side,” Thordarson said. “It had its kill switch turned on.”

Tyr took off down the trail toward a paved road.

Thordarson ran after Tyr for a quarter mile. Just as she was about to round the bend, the dog came back, she said. Thordarson found her horse.

Four women hiked toward Thordarson down the trail with the dog, which wasn’t on a leash, she said.

Thordarson said she asked for the owner’s information and received a phone number that’s disconnected, she said.

“Even if the dog and owner are not found, we appreciate the support and hope this incident helps bring all trail users together to promote safety and awareness,” Thordarson said. “These beautiful trails belong to all of us – cyclists, hikers, families, equestrians.”

Contact the writer: 714-796-2254 or eritchie@ocregister.com or twitter: @lagunaini