Why is my dog's poop smaller after switching to Royal Canin?

Changing diets can certainly cause changes in stool appearance and size. The Royal Canin hypoallergenic diet is a higher quality diet than Kibbles and Bits, which typically results in less waste due to fewer filler ingredients. Higher quality diets often result in slightly smaller and less frequent stools. If Spock had an obstruction, I would expect profuse vomiting, anorexia and lethargy, so this sounds unlikely. As long as Spock is eating and active with no evidence of vomiting or diarrhea, it doesn't sound like there is cause for concern! :-)