I brought home a 4 mo. male Blenheim to my 8-1/2 yr. neutered male Tri on October 23. They also had met at the breeders and seemed to be fine. I introduced them in the back yard, and the older dog just evaded the pup. Upon going in the house, he snapped at the pup whenever the pup came close to him. He'd also snap if I picked the pup up. So the pup spent alot of time in his bed the first day or two--avoiding any confrontation. (I didn't interfere much between them.) The third day he was more tolerant but still a little "sulky." He wouldn't even greet my husband when he came home from work -- just like he was punishing us for bringing the pup home. Bottom line, within 10 days there was no more "snapping."
Each day got better. We drove 2-1/2 hrs. each way this past weekend to our home at the Jersey Shore. The older one had always made the trip on my lap. I put a blanket across the back seat. Put the pup in first and Casey second. Within 10 min. they were snuggled up together. I would have never imagined it from the first week!
One thing I did from the beginning: Casey sleeps in a crate in our rec room at night. I put Alfie's crate right beside his from the start. It worked out very well--he slept all night from day one. I think this also helped with the "adjustment" of a new pup.
Casey 9 yr. Tri, Alfie 1 yr. Blenheim