
Very good questions for a thread I think!
My very lowest point was mating a bitch of my second breed for the first time (i.e. my first time with the breed), and she gave birth two just two puppies, both of which were dead -and she was so depressed afterwards it was absolutely heartbreaking. Mated her a second time, both scans said two pups, and she gave birth to two pups -both dead again. At that moment I felt so low it was indescribable. When suddenly a third pup appeared, ALIVE, it was one of the high points for sure.
Otherwise, in my main breed, lowest point was having 9 pups born but almost all the buyers dropped out so I only got homes for 4. The stud dog owner and I own 5 of those pups between us and having more than one pup to train is a nightmare. Highest point is seeing my pups all grown up taking major awards at shows and in obedience and agility -nothing beats it.