SHAWANO, Wis.—Atop a wooded hill here in the heart of America’s Dairyland, an industry legend was recently laid to rest.

It wasn’t some milk magnate or a famed innovator, but an ornery, 2,700-pound bull named Toystory—a titan of artificial insemination who sired an estimated 500,000 offspring in more than 50 countries.

“He was a dream bull,”...