When they arrived, the man had already suffered from cardiopulmonary arrest – a condition when the heart and lungs stop working, resulting in death.
He was pronounced dead on the scene.
Chateau du Golf de la Freslonniere in Le Rheu is a 17th-century castle surrounded by 140 hectares of private land, including a golf course.
Local media reports that his planned burial was illegal and that he should have contacted a specialist equine cremation service.
Additional reporting by Maria Ortega