Authorities did not know why the wildebeest, also known as a gnu, attacked 64-year-old Klaus "Dick" Radandt, but said the animal may have been protecting his mate.
The animal apparently knocked a pen gate off his hinges, used his head to ram Radandt multiple times and then repeatedly stepped on him once he was prone, said St. Joseph County Coroner Chuck Hurley.
The investigating police officer from St. Joseph County said wildebeests become aggressive this time of year because it is the beginning of mating season. The animal may have perceived Radandt as a threat, he said.
Radandt's wife, Terrilyn, found him in the barnyard Sunday after he failed to return for lunch. Family members declined to comment to the Tribune.
The gnu was one of three the Radants own, in addition to ostriches, emus, reindeer and llamas.