In Spain, "pan de perro" is mentioned as early as 1623 in a play by Lope de Vega. It is used here in the sense of giving someone blows; to "give dog's bread" to someone could mean anything from mistreating them to killing them. The latter meaning refers to a special bread (also called zarazas) made with ground glass, poison and needles and intended to kill dogs.
There are no regulated dosage recommendations for CBD for dogs — or even humans — at this point. What’s more, there aren’t even any generally accepted guidelines about how much CBD for dogs is effective for certain conditions, even taking weight into consideration. So you’ll notice that each company can differ significantly in the amount of CBD in each treat and the number of treats they recommended.