Sadly a highly inheritable trait........most breeders will check for signs of this carefully, particularly when the kid is 'out' at disbudding time. At one time, before meat kids werein vogue, these kids showing signs of fish tail teats were PTS.
There are more about these days because the huge dairy herds are not as scrupulous about checking. Also, a lot a new goatkeepers buying from commercial herds, assume that all will be well.......sadly finding out later that the opposite is the case. It is only perhaps 2 generations down the line, this fish tail deformity reappears with the sad result identified.
I personally, however well bred a kid is, would put such an animal to sleep.