It was extremely dangerous to do tail docking by the roadside, with sedation being the bulk of the problem.
In a proper hospital, there would be a dedicated anesthetist stationed in each operating room. Veterinary hospitals had specialized anesthetists, too.
It was even more difficult to sedate an animal than a human, as different animals had different tolerances to sedation. If it was too low a dose, the animal would wake up before the surgery was over, but if they gave too much, the animal wouldn't wake up. Therefore, they would have to weigh the animals before surgery and administer the right amount of sedation according to that.
But this vet wasn't running an official clinic, nor did he prepare a scale. He had determined everything through his own experience and judgment. He picked up a puppy and estimated its approximate weight before preparing everything.
