minecraft-assets/assets/minecraft/loot_tables/entities/horse.json

{
    "pools": [
        {
            "rolls": 1,
            "entries": [
                {
                    "type": "item",
                    "name": "minecraft:leather",
                    "functions": [
                        {
                            "function": "set_count",
                            "count": {
                                "min": 0,
                                "max": 2
                            }
                        },
                        {
                            "function": "looting_enchant",
                            "count": {
                                "min": 0,
                                "max": 1
                            }
                        }
                    ]
                }
            ]
        }
    ]
}