AUGUSTA – State officials said Tuesday that they still have no conclusive cause of death for seven horses found dead last month and three euthanized later at a Searsport farm, but they are looking at accidental poisoning.

State veterinarians with the Maine Department of Agriculture initially launched an investigation into Kathy Hecht’s treatment of the horses at her small house on Mount Ephraim Road.

Animal Welfare Division veterinarian Christine Fraser said Tuesday that a pathologist from the University of Maine in Orono did a necropsy of one of the dead horses, and “no cause of death was found.”

“We are pretty sure it is not an infectious disease,” Fraser said. “It is possibly a toxin. We have no proof that this was intentional or accidental. We have no proof the owner did it or that anyone else did it, so my guess is accidental.”

State Veterinarian Don Hoenig confirmed Fraser’s assessment. “Right from the start, the local veterinarian was not concerned that this was an animal cruelty issue,” he said.

Tests on the horses’ feed and blood tests are pending, and some tests were sent to the University of California for screening for toxins, he said.

“This is very, very tragic and unusual to have such a high herd loss,” Hoenig said.

Hecht reportedly brought 35 horses to Maine from North Dakota in 2004 and almost immediately caught the attention of animal welfare agents.

Fraser said she had been working with Hecht on the horses’ care, and that Hecht had complied with every suggestion.

“She was working with us and following through,” Fraser said. “Under the law, we couldn’t seek a seizure order.” She said that when she began working with Hecht, the only issues were an inadequate shelter and corral. The horses all had food, water and medical care, Fraser said.

After the mass death of seven horses, seven others were removed from Hecht’s farm and taken to Goose River Farm, the home of Lynn Boynton of Swanville, where she and her husband keep several horses. Three of the horses later were euthanized.

Boynton said Tuesday that the horses were underweight. One still cannot stand and another has an abscessed eye. All are experiencing massive hair loss.

Some of the possible poison sources are botulism and someone feeding the horses cattle grain, which is treated with monensin, a growth additive for cattle and poultry that is toxic to horses.