11.1 Definitions of a breed (2024)

One of the opportunities of crossbreeding is that in our managed species many breeds are developed and that much of the genetic diversity in these species lies between breeds. Many definitions for breeds are given in the literature, summarized and discussed.

At first sight the definition found at the website of Oklahoma State University: “Animals that, through selection and breeding, have come to resemble one another and pass those traits uniformly to their offspring.” However, it misses a key requirement, namely a necessary and sufficient list of traits that are passed uniformly for the breed in question. This necessary and sufficient list of traits, when defined, is often referred to as the breed standard, although breed standards may sometimes be the description of the characteristics of the “ideal animal” described in the breeding goal.

Therefore, farm animal geneticists lean towards the definition of Lush because it emphasizes the role of the breeders as the owners of the breeding animals who are the decision makers: “A breed is a group of domestic animals, termed such by common consent of the breeders, ... a term which arose among breeders of livestock, created one might say, for their own use, and no one is warranted in assigning to this word a scientific definition and in calling the breeders wrong when they deviate from the formulated definition. It is their word and the breeders’ common usage is what we must accept as the correct definition.”

After a long discussion on the definition of a breed in an FAO meeting, Keith Hammond concluded “A breed is a breed when enough people say it is”.

One conclusion is that a rigorous universal definition of breed is not possible as it will depend on the context of the user. In the context of this textbook an operational definition of the FAO provides a robust reference point:

“A breed is a sub specific group of domestic livestock with a common history whose members are treated in a common manner with respect to genetic management”.

Source: Oldenbroek, J.K. (2017). Genomic management of animal genetic diversity. Wageningen Academic Publishers, The Netherlands. ISBN: 978-90-8686-297-9.