Here is my experience on this subject:
Used to be a financially succussful middle distance & sometime distance runner.
A few times I recall doing what for me were very mild cross-country training runs with my sisters dobermans. The first time was in 1985 with one dog and the second time was in 1987 with another dog. Both dogs were dobermans. The first dog was a male, the second was a female. Both times were in the summer with the temperature in the middle 70's. Both dogs had to be put down not long afterwards. I recall the pacing was nothing difficult, about 5:00 to 5:30 per mile pace over about 3 miles. Both dobermans were considered very active, but after the first mile they seemed to loose interest.
Did not realize what was happening at the time and regret it. Only later in a conversation with another competitive runner who is also a dog-owner saying that he would never put his dog through the sorts of training that a class runner does on a routine basis since they just aren't built for it.