Talk about your niche advertising. This isn't a promo for dairy products in general or milk in particular. It's an ad for a specific milk bottle sealing system. Nice art, though. I can barely remember glass milk bottles with cardboard caps. Through most of my youth it was waxed cardboard containers, with either a flap closure (quarts) or a rather clever fold-out spout (half-gallons). Though people could still get their milk delivered, we always bought ours at the grocery store.
Link to the book:
Amazing But True - Facts About Milk and Milk Protection