Do animals need proficiency in that type of armor to avoid penalties?

@JeremyECrawford When wearing barding (PHB p. 155), do animals need proficiency in that type of armor to avoid penalties(PHB p. 144)? #DnD

— Jesse Smith (@jesselsmith) June 17, 2016

The rule on monsters and armor is purposefully generous and is ultimately in the DM's hands. See MM p. 9. #DnD https://t.co/1UQlGYnPZY

— Jeremy Crawford (@JeremyECrawford) July 14, 2016