​It is generally thought that Milk Day was created to celebrate the first time milk was delivered in glass bottles. Prior to this, conditions for milk delivery were fairly unsanitary but the new bottles enabled safe and clean storage. However, Milk Day soon grew to be a day dedicated to all aspects of milk. Whether it is the health benefits of drinking it through to the farming industry that produces it, the day can be used to celebrate the wonders of milk. Source: https://www.daysoftheyear.com/days/milk-day/