Goat horns Don't use use_cooldown Custom Cooldowns
To reporduce -
1) Give yourself Custom Horn
/give @p goat_horn[use_cooldown=\{seconds:30}] 1
2) Use horn, and see that it still uses the default cooldown time
To reporduce -
1) Give yourself Custom Horn
/give @p goat_horn[use_cooldown=\{seconds:30}] 1
2) Use horn, and see that it still uses the default cooldown time