Jersey Breed

What Is A Breed?

The classic definition of a "breed" is usually stated as a variation of this statement. "Animals that, through selection and breeding, have come to resemble one another and pass those traits uniformly to their offspring."

Unfortunately this definition leaves some unanswered questions. For example, when is a crossbred animal considered a composite breed and when do we stop thinking about them as composites? Perhaps this definition from The Genetics of Populations by Jay L. Lush helps explain why a good definition of "breed" is elusive: "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."

As you can see from Dr. Lushes definition it is at least in part the perception of the breeders and the livestock industry which decides when a group of individuals constitutes a "breed".

The development of the breeds takes different routes also. In some breeds you can see the amount of change that can occur as the result of selection for a small number of traits. As an example, Holstein cattle have been selected primarily for milk production and are the highest milk producing cattle in the world. Other breeds have traits that result from natural selection pressure based upon the environment in which they were developed. An example of this might be the N'dama cattle from West Africa. These animals have, through the centuries, developed a resistance to trypanosomiasis or sleeping sickness spread by the tse-tse fly, which is fatal to most other breeds of cattle.

Why are we concerned about preserving information about minor, or relatively unknown, breeds of livestock? Is there a reason for the preservation of minor breeds of livestock? Couldn't more improvement be made if there were fewer breeds?

Well, lets go back to our Holstein example again for a moment. While the Holstein clearly has an advantage over other breeds in the production of whole milk, this advantage is based on feeding high levels of cereal grains and pricing that favors low milk-solids content. A drastic change in either of these factors could result in a decrease in the advantage of the Holstein. Given these conditions perhaps a breed that is currently rare or endangered, such as the Dutch Belted, which displayed excellent milking ability in a grass-based dairy situation in trials in the early 1900's, would find itself on the forefront. In Australia, composite breeds, such as the Australian Friesian Sahiwal, have been developed which have higher milk production levels than Holsteins in the tropical regions of that country.

Therefore, if for no reason other than maintaining a genetic pool which someday may be needed 1) to offset a naturally occurring inheritable weaknesses, and 2) to meet the potential challenges resulting from changes in production resources and market requirements, it makes medical and economic sense to maintain "exotic" breeds for their genetic diversity and their potential contribution to cross-breeding out weaknesses and disadvantages.

The above is adapted from

"Breeds of Livestock "

Department of Animal Science at Oklahoma State University

http://www.ansi.okstate.edu/breeds/