I attended a lecture some years ago on genetics. The lecturer was a vet. Somehow during lunch there was a heated argument regarding tail docking and the nervous system of new born puppies.
When the lecturer rejoined us in the hall she decided that she would outline a few things very quickly so she could get everyone back on subject.
A new born puppies nervous system is not fully developed for the first 3-4 days, it is however developing. Unlike human babies, unlike lambs which are. They find their mothers thru heat. The twitching new born puppies do assists in the development of their system and is necessary for their development. A puppy should twitch at least once every two minutes.
To shut the subject down she said that while she did not perform tail docking she would in short tell us that the pain felt by a newborn puppy is not at the same level as a lamb. And yes I know why they dock lambs tails.
Now before I get blasted let me just say, don't shoot the messenger. I do not own a docked breed. I am not even having the dew claws removed from my whippet puppies even though the majority are removed at 2-3 days old. Why you might ask? Well the sire of my litter has his dew claws and the remainder of my dogs don't. Of all the nails I have to cut, these are the only ones that for some reason I never have to???