I know I'm a little late with this, but it's the Cornell study on the comparison of penning and tethering of sled dogs.
http://www.naiaonline.org/uploads/Wh...ng_and_pen.pdf

It also states that beagles, when penned in smaller pens were much more active than those penned in larger confinements. Most likely this is due to being more active with the dogs near them, since they were closer to their neighbor.