I bred and docked my first litters of pems in the late 1960's and early 1970's. There was a long break while I raised my four sons and bred some golden retrievers. I resumed breeding pems with the purchase of our lovely Yoda nearly sixteen years ago. Because of changes to our laws I have been leaving tails on for nearly a decade.
Occasionally human children are born with an extra digit and when this happens the doctor 'bands' it to cut off the circulation, causing it to fall off after a short while. This is the same procedure which breeders use to shorten tails. It is not cruel, nor is it painful.
We have not found any adverse health issues resulting from the tail now being left on, however if one of our red and white corgis were to find their way into our neighbour's properties they would be shot on sight as they look so much like foxes. This may be why UK farmers began docking in the first place. This consideration is obviously of no consequence to breeders and owners who keep their dogs as house pets but for those of us who live an agricultural life it is still a very real concern.
We experimented with the nbt gene but after several litters realised we would not get the quality of breed type, particularly movement, that is such an important characteristic of the pembroke corgi and so abandoned any further attempts. We are also aware that many of the corgis that carry the nbt gene are banded in the old fashioned manner to remove half and three quarter tails to improve their cosmetic appearance. This practice seems counterproductive at best and hypocritical at the least.
As we are able to breed and keep more than the usual number of dogs we have had the opportunity of comparing different tail sets and carriages. As a general rule we have found that pems with tails carried down tend to have a sloping topline and a weaker rear drive. This finding is consistent with the UKKC's requirement in their breed standard that the pembroke corgi's "full length natural tail is set on line with the topline, and may be carried out behind the dog, straight up perpendicular to the back or curved over the back in a graceful sickle."
In recent years we have had the opportunity to import dogs and bitches carrying useful genetics. Some of these have been legally docked in their country of origin. The tail vs no tail argument does occasionally skew a show judge's opinion in an irrational and sometimes unfair manner but overall we are prepared to accept curling tails and high tail carriage and some erratic decisions as a very reasonable price to pay in order to maintain overall breed type and powerful rear movement.