NEW YORK - John A. Hoyt, who made the Humane Society of the United States the largest anticruelty organization in the country in an era in which changing cultural attitudes were greatly expanding the number of animal protection groups, died April 15 in Fredericksburg, Va. He was 80.

The cause was progressive supranuclear palsy, a rare brain disorder, said his daughter Peggy Hoyt.

Mr. Hoyt, who was president and chief executive of the Humane Society from 1970 to 1996, was best known for expanding its traditional stewardship over dogs and cats to include laboratory animals, livestock, wild horses, whales, endangered fish, and rodeo bulls.

The society’s expanded agenda reflected both cultural sensitivity and public relations savvy as environmentalism and the animal liberation and natural food movements were emerging, said Bernard Unti, a historian of the Humane Society. The new movements were expanding public consciousness, but also competing for contributions.

“It was a rapidly changing landscape,’’ Unti said, “and John made sure that the society blossomed while continuing to be itself.’’

Mr. Hoyt also established the Humane Society as one of the most sophisticated lobbying operations in Washington. He began campaigns to save porpoises and baby seals. He worked against fur trapping, sport hunting, roadside zoos, cockfighting, and bullfighting and fought to end unnecessarily painful lab experiments on rats, mice, and chimpanzees.

The suffering of livestock became a major focus of Humane Society lobbying in the mid-1970s, soon after Mr. Hoyt met Temple Grandin, the animal behaviorist, who was then developing a stress-reducing corral for young cattle being slaughtered for veal.