The answer is Simple:

Stud Goats meet the breed standards set by the Boer Goat Breeders' Association of South Africa and the Kenya Livestock Breeders Association. They have the right conformation, colour, and genetic traits required to be classified as stud animals.

Flock Goats don’t meet these strict breed standards but still have no cull defects. They are mainly used for commercial meat production and breeding.

Both have their place in the industry — stud goats improve genetics, while flock goats form the backbone of commercial meat production.