After Mr Spratt had started to make his dog biscuits and sell them worldwide, the next big thing to happen was to be when machines took over from horses in doing all our hard work. Around the early 1900's there were just too many horses surplus to requirements and so they were turned into dog food. Eventually horses were bred just for the purpose and sold as a tinned dog food.
The next big change was during World War II when a shortage of tin meant that the dog food manufacturers had to come up with a new idea. Essentially this was the start of the dry kibble type product we know today and what's interesting is that the nutritional needs of the dog were not considered at all - it just needed to have a long shelf life and not be a tinned product. The simple reason there are so many unnecessary carbohydrates in commercial dog food is because they dry easily, keep for a long time and are much cheaper than protein - not because it's what dogs should be eating.
In 1964 the Pet Food Institute began a campaign to stop people feeding their dogs anything but commercial dog food.
Last year, pet food companies in the US spend $16 billion promoting their products.