A Canadian farm family says they will “never recover” from the heartbreak of seeing more than 300 ostriches killed in a government-ordered cull that had been opposed by American celebrities and officials including the American health secretary, Robert F. Kennedy Jr.

“In a way I feel like I failed ‘cause I couldn’t protect my mum,” the farm owner’s daughter told the Canadian Press news agency through tears as dead ostriches were loaded into containers in the field behind her this week.

“Our land that had so much life 24 hours ago is a cold, empty shell,” continued Katie Pasitney, who described the anguish felt by her wheelchair-bound father. But, she vowed, “We’re going to use that as motivation and we’re going to change Canada.”

Officials with the Canadian Food Inspection Agency ordered the cull late last year following an outbreak of avian flu, or H5N1, that killed 69 ostriches on the British Columbia farm. Two additional birds were found to be infected when CFIA authorities tested the rest of the flock.

The family fought the order through the courts, attracting international attention and the support of major American political figures along the way.

Among those who took up the cause was New York billionaire and Republican megadonor John Catsimatidis, who became interested after Ms. Pasitney called into a radio show that he hosted in May, according to the BBC.

“The Canadian government wants our farm killed” on the basis of just two birds that tested positive, she told him, “even though they are fully healthy and doing amazingly well.”

At Mr. Catsimatidis’ urging, Mr. Kennedy got involved, meeting with Canadian officials to propose collaboration on a long-term study of the ostriches to see if they had developed immunity to the avian flu. The idea was rejected.

The administrator of the Centers for Medicare and Medicaid Services, Mehmet Oz, at one point offered to have the ostriches relocated to his property in Florida, but the family declined, preferring to keep the ostriches in Canada.

In July, Dr. Oz and Mr. Catsimatidis made their case directly to Prime Minister Mark Carney, who has not commented publicly on the case.

Bird lovers also became involved, at one point bombarding the phone lines of companies ranging from hotels to gas stations to waste management companies that were thought to be involved in planning for the cull. The Royal Canadian Mounted Police said some of the  companies complained of harassment and one company said its workers received death threats.

The CFIA authorities remained unmoved, insisting the cull was necessary for public health reasons as the case worked its way through the courts. That long journey reached its conclusion on Thursday when the Supreme Court declined to get involved.

Within hours, CFIA workers in hazmat suits descended on the farm and went about their grisly business, using firearms to dispatch the birds behind a screen of hay bales. “It’s important that the minister of agriculture and CFIA are able to protect the health of the general Canadian public and the food we consume,” Justice Minister Sean Fraser said.

For Ms. Patisney, the ostriches are gone but the fight is not over. Vowing to make her farm “ground zero for change,” she says she is now focused on steps to protect other farmers from what she calls a “broken” system that has failed to prevent the spread of avian flu.