I did this tee shirt many years ago for a herding event.
"Go bye" or "Come bye" is the traditional (in the UK and USA) command for the dog to swing clock-wise around the livestock.. "Away to me" is the traditional command for the dog to swing counter-clockwise. Don't ask me how these particular commands arouse, because I haven't any idea whatsoever.
In the cartoon, the "go buy" dog is a Bouvier, purse on one forearm, pushing a grocery cart full of food, mostly meat but some vegetables. The "a weight" dog is a very obese Bouvier standing on a scale. Arrows indicate the two directions.
The message of the shirt is that a dog allowed to eat as much as he pleases is likely to become obese. An active herding dog can burn off more than the same dog would as a couch dog, but still the owner has to regulate (measure) food intake.
The dog in the cartoon is my adored Chelsea, whose great natural talent for herding sheep and cattle was as good as I've ever seen in any dog of any breed. She also was quite fond of food and would gladly have eaten 3 times her needed maintenance diet. It would not have taken her long to become the obese dog in the second part of the cartoon.