Hey dama
Look for hunting breed mixes... Any dog with Spaniel or Terrier in his/her blood is a good start, and not too big. Leni is a Brittany/Dackel mix. Dackel is what we call Dachshunds here, but the long-hair variety, not the really low, long 'Wiener Dog' type, lol. (but make no mistake, those little guys can outrun a horse, and most humans)
She's about 20lbs and can basically run all day, every day. I've had her on about 5 or 6 thirty-milers and each time, at the end, she's like, so when are we gonna RUN? I have her on a leash on long runs like that so she doesn't burn herself out early on by sprinting off into the forest.
I have a friend with a large-ish Jack Russell. That dog can run like Leni. I've also had conversations with two different people at two different marathons who sought out huskies specifically as running dogs, and both were completely disappointed. The dogs have the physical abilities, but they need the motivation, the team, the tundra, the sled... Without that, they just quit after a couple miles...
So, I think the breed plays a big role. Think about a Retriever's 'job' - jump into the lake, get the duck, bring it to the boss. Nothing in there that involves tracking prey across hill and dale, and sticking to the job till it's done... They don't want to do that and you'll never convince them otherwise. I would think their size/weight would work against them over long distances, too, as you pointed out.
Oooops, rambling with SwiftKey lol.. Gonna move this to a dog thread later.
Now back to our regular programming
