"...when the last individual of a race of living things breathes no more, another Heaven and another Earth must pass before such a one can be again."
-William Beebe

ALBC News Sample Article: July/August 2011

What is a Breed?
And Why Does it Matter?

By D. P. Sponenberg

ALBC has long been working (successfully!) to save breeds. A large and capable community of breeders, consumers, scientists, and other advocates are committed to this cause. It is important for everyone involved in this work to know what breeds are, and why it is important to save them. A deep understanding of breeds can powerfully inform and shape effective conservation programs at all levels. This knowledge is especially important when resources might not provide for saving all breeds in all situations. When not everything can be saved, wise choices need to be made in order to save as much as possible, and to save as many breeds as possible, and to save them effectively so that the next generations of farmers and consumers have the same broad choices available that our generation has enjoyed.

Breed definition was once easier for me, but it is now getting somewhat more complicated. The most basic definition, and the one that some have adopted for a variety of political and strategic reasons, is that a breed is “anything anyone says it is.”  This includes a wide variety of populations, and the end result is that this broad definition does not really do much to help in assessing the relative value of those populations as units of biodiversity in domesticated animals.

At the other extreme is an approach only recently made possible by the wide availability of molecular genetics testing. This approach is to define breeds by the specific, identifiable genes they contain, focusing on the most common variants as being typical of the animals of the breed. The definition is “breed = identifiable package of specific genes.” This approach assumes that the techniques are capturing all, or at least most, of the relevant genetic information contained in the animals being considered.

I find that a very useful general definition lies between these extremes. This definition holds that a breed is a group of animals whose individual members resemble each other closely enough to be readily recognized, and that reproduce this same breed type when mated together. This definition implies a level of genetic uniformity within the breed that assures predictability, as well as agreement among a group of breeders about the characteristics that define the breed. This basically defines a breed as a phenotypically identifiable and somewhat consolidated genetic resource. In that sense this definition is very useful in helping to determine conservation priorities. This definition is basically “breed = genetic resource,” although some will fault it for being driven by appearance and production rather than by molecular techniques. A key point is that the appearance and production are both driven by the underlying genetics, so that uniformity in the first two indicates uniformity in the third.

This definition, by and large, drove most breed development over the last few centuries, which is when most breeds were developed. Producers and breeders had goals, wanted predictability, and mated animals with those goals and that predictability in mind. They were isolating genetic pools, to varying degrees and by various means, but all without understanding the finer points of genetics, and certainly without the ability to measure individual genes. Today, molecular genetics can peek into the genomes of these animals, and the increasing tendency is to use molecular techniques to replace the older practices of master breeders who could rely only on appearance and production. The two approaches do not necessarily lead to the same endpoint, although both have a place in breed development and breed conservation. It is always important to remember that appearance and production are both based on the underlying genetics. Focusing on appearance and production rather than on genes identified by molecular techniques does not mean that the appearance/production technique is necessarily a non-genetically-based strategy.

The “breeds as genetic resources” definition can drive conservation decisions in a few ways. One is that it allows decision-makers to focus on the degree to which populations satisfy the definition, leading to a ranking of populations as to the degree of genetic consolidation or uniformity (and therefore predictability) inherent in the candidate population. A second would be an evaluation of the relative uniqueness, or lack of relatedness, when compared to other populations. All of this analysis can be genetically driven, and can be rapidly taken to a very objective analysis and decision.

“Breed = genetic resource” is a convenient and reasonably objective definition, and allows conservation to encompass anything that leads to saving the genetic resource. Cryopreservation, exhibition/demonstration herds, and the more usual production herds all qualify and have important roles to play.

A more global view of breeds and their roles in current and past agriculture (or more broadly, human life, history, and endeavor) needs to encompass factors other than the strict genetic resource definition. Importantly, each breed lives and persists in a somewhat peculiar environment. The environmental component has important constraints imposed by influences from the natural environment. Indeed, most observers generally think “natural environment” when “environment” is encountered without further definition. Importantly, though, agricultural resources are also affected by selection decisions made by breeders, as well as by husbandry practices of human owners. For the species of interest to ALBC, the selection pressures of this uniquely agricultural environment determine the ongoing genetic structure of the breed. Without these environmental constraints (determined by nature as well as human decision and practice), the breed will change from its original form. For this reason breeds are most effectively conserved in their original habitat and under their original management. Ongoing conservation of breeds in their environment also allows the breed to slowly adapt to changes in the environment, and this can be an important component of long-term survival as environments (both natural and human-influenced) change.

In this sense, then, the definition becomes “functional breed = genetic resource + natural environment + human management and selection.” This takes effective conservation to a very different endpoint, because breed populations must be kept as ongoing genetically viable groups in an appropriate environment and under appropriate management and selection. This almost always requires living populations of animals in a productive setting, and this really needs to be a large chunk of the goal of effective breed conservation. While this does not rule out cryopreservation (which can be an incredibly useful tool), it does imply that living populations are the ultimate goal and that these need to be carefully maintained and monitored.

As in much of life, it is not always possible to “have it all.” In some cases, saving the genetic resource may be all that can be done, and in this situation cryopreservation is certainly a powerful and useful tool as a final endpoint. This removes both “natural environment” and “human management and selection” from the equation. Other situations remove only one or the other of these factors, and can change the final outcome. For some feral livestock, the component of “natural environment” may be impossible to maintain due to removal or eradication programs, and acknowledging the resulting change in final genetic outcome can be useful in informing conservation programs. For other breeds, the “human management and selection” piece may have to change radically from past practices due to changes in societal demands for animal welfare. In each case the changes can be acknowledged, and in many cases can be at least somewhat counteracted by wise decisions in population management and selection that allow the original resource to persist without significant change in overall genetic structure.

The short version of all of this is:

A breed, in the narrow sense, is a genetic resource that is externally and genetically uniform enough to be recognizable from other animals of the same species, and that reproduces the parental type when mated to other members of the breed. A functional breed is a combination of the genetic resource, but also includes the natural environment as well as the human management and selection pressures exerted on this resource.

D. Phillip Sponenberg, DVM, Ph.D. is a Professor of Pathology and Genetics at Virginia Tech, in Blacksburg, Virginia. He is a long-time member of ALBC, and serves as a Technical Advisor to the ALBC staff.  He can be reached via e-mail at [email protected].

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