I think it’s got a lot to do with the individual dog’s metabolism and exercise levels primarily, and other influencing factors such as his sense of well-being, i.e. his mental health.
You’ve all seen pictures of my Staffies just like Ryan’s, they are exactly half his dog’s age, but every time we come across another knowledgeable dog owner, that person is absolutely floored when we tell them they are nine years old. The dogs also only eat Pedigree dog biscuits, but the big difference from Ryan’s is that they also eat (every meal) either one egg each or a serving of venison mince. Periodically they get a cattle beast leg bone to gnaw on in order to keep the teeth in tiptop condition, which in turn reduces the canine halitosis to perfectly acceptable levels.
My observation with the Staffordshire Bull Terrier is that if they do not get the egg and meat then their coats and general condition suffers, you will notice the change in condition within a week if they do not get it. The flipside of this is that if they do not get the requisite exercise levels then some dogs will put on weight quickly. Our bitch can eat three servings a night and you would never notice the difference, but my dog is prone to lardiness. So his portions are carefully managed.
Both dogs will run in front of the quad up a farm track that climbs 400m vertically to the trig at the top, hunting every face and gully on the way up, and every face and gully on the way down... I wish I could do even remotely similar.
Bookmarks