I just wrote a comparison between this and dog breed standards - it disappeared so here is a potted version.
The Kennel Club is the Governing Body for dogs.
Each breed club or group of clubs together as a Breed Council, has drawn up (or for new breeds draws up) the relevant breed standard, which includes shape, size, weight, colours etc
This standard is then submitted to the Kennel Club for approval, and once accepted and printed can only be changed after consultation with and the agreement of the kennel Club
I'd have thought that would be the case for the Poultry etc governing body - the National Poultry Association maybe?