bedrock-samples/resource_pack/render_controllers/saddle.render_controllers.json

{
  "format_version": "1.8.0",
  "render_controllers": {
    "controller.render.saddle": {
      "geometry": "Geometry.default",
      "materials": [ { "*": "Material.default" } ],
      "textures": [ "Texture.saddle" ],
      "part_visibility": [
        { "*": false },
        { "body": "q.is_saddled" } 
      ]
    }
  }
}