You smell different
After Elsa's friend Yogi was neutered, she had to wait for three weeks until they had a playdate. Before he came over I gave his Mom a heads up. I explained to her how Elsa was going to behave. There would be much sniffing. In fact the week before he came over, Lucy had come over and Elsa had sniffed her like crazy. She had the "different' smell on her as well. Yogi's scent had changed and Elsa wasn't sure what this new smell was. "Watch closely when he first arrives" I said; because it will be over very quickly.
Sure enough when Yogi and Lucy arrived for their next playdate, Elsa kicked into action. Her whole body changed from just excited to concerned, excited. For a fraction of a second, Yogi smelled different. He might have been someone else, a stranger. Elsa's body was tense for that instant of crazed "new dog" sniffing. Within seconds it was over and all was back to normal. It was indeed the old Yogi, albeit changed.
A friend of mine had told me about this scent change several years ago. I hadn't heard of it until she explained about her experience; and I hadn't seen it until Penny was spayed. After hearing about this big scent change I was interested for Penny's first visit after being spayed. Having two highly aware dogs (Luke and Elsa); I was sure that they would notice, and they did. The heightened sniffing began as soon as they got within sniff range. Penny charged in like any other day, but something was definitely different this time. Both Elsa and Luke sniffed her like mad. She certainly smelled different to them. But just like with Yogi, it was over very quickly and they continued on.
A dog's sense of smell is so far beyond ours. It amazes me when they obviously scent that a critter has been in our yard. Elsa is an over the top scent dog; and if I can ever find a close enough scent class she will be in it. I find it amazing that they can actually smell the difference between intact and altered. It was very obvious both times I have experienced it now. To see it you must be looking for it.
Seeing it in your own dog is difficult because they will be sniffed like mad when they get home from the Vet. no matter what they had done. But seeing a friend dog be sniffed like this after altering is very telling. The only difference in the dog is the altering and it is a HUGE difference for dogs. After all scent is big for dogs; it is typically the first sense used for most activities.
Oh yes, they smell different. They smell a whole lot different after being altered. We just can't tell the difference because we are mere humans.