I have a six month old yellow lab. He is a great dog from an excellent bloodline and is full of energy. Up until recently he was responding very well to the training, but a few weeks ago he sustained injuries to both front paw pads so I didn't get to work him for some time. I just started working with him again and he is responsive to every command (sit, stay, heel, whistle commands, ect) but will not retrieve. He will get on heel but when I toss a bumper he will run to the mark but turns around and come right back to me without the bumper. I tried going back to square one by tossing a bumper a few feet out and sending him. A few times he picked it up but did not return it to hand. I do not know what could have caused him loose his drive to retrieve when he was not missing a beat during training sessions prior to his injury. I did just move into a new house where I put a pen in the back yard. This is where he spends him time now when I am away versus staying in his crate before. Im not sure if this has anything to do with this behavior. I never over worked the dog and kept the training sessions short and fun so that he would not loose interest but now its as though he forgot everything he learned and is not willing work. I tried searching the web for possible solutions but found nothing, can anyone offer some insight on how I can correct this issue and get my dog back on track.