Thursday, November 14, 2013

Poultry breed purity

D. Philip Sponenberg, DVM, PhD, professor of pathology and genetics at the Virginia-Maryland Regional College of Veterinary Medicine, wrote the following article for The Livestock Conservancy News Summer, 2013 issue. It's available to members but they gave me permission to reprint it here. I've added some photos of foundation poultry breeds -- the Java, the Cochin, Dorking, Chantecler and Polish

“Breeds” – Livestock and Poultry

Breeders of poultry and breeders of mammalian livestock often are thinking different things when they think “breed.” Exploring these differences can help to facilitate communication and can also help to advance effective breed conservation. For this article, “poultry” will mean avian breeds, and “livestock” will mean mammalian breeds, even though these are hardly ideal definitions all the way around.
Donnis Hedley's Mottled Java shows what a good mother she is.
Breeders of both poultry and livestock breeds do agree that the basic characteristic of breeds is their consistent appearance. That is, one breed is usually distinguished from another because it has an array of physical traits that are repeatable and unique to that breed. This uniformity comes down to the present in different ways, though, and these differences are where poultry and livestock often differ.

In the minds of most livestock breeders the uniformity of breeds results from the expected interactions of foundation (what goes into the original mix), isolation (so the mix is not further jumbled or changed along the way by outside stock), and selection (which specific animals breeders choose to keep, and which they choose to reject). In most cases a fourth dimension is piled on here, which is that the whole result is functioning in a specific environment, along with people, for the purposes of production.

Reliable Poultry Publishing Company used these Buff Cochins as an example of the breed in the early 20th century.
This whole process of breed formation tends to give a final phenotype (basically, what can be seen or measured) almost as a secondary result. The cascade of events starts with foundation (what was available), then isolation (nothing else was available!), and selection (breeders needed the animals to do this or that) and the result was animals shaped by the interactions of these three in the environment and serving people. This process results in a certain degree of uniformity.

The uniformity can then be taken a final step as a more deliberate process when breeders organize, notice the similarities among their animals, and then deliberately eliminate some rare variants that do not fit the majority package of traits. This final step is breed standardization, but in most cases it was the crowning final event on a process already leading to the end result of reasonable uniformity.

For many poultry breeds this same process of breed development has occurred, resulting in breeds that function biologically in exactly the same way that livestock breeds function. But for poultry, a second pathway has become nearly as important as this first, and poultry breeders do not reliably distinguish between these two pathways in either their thinking or their practices.

My own White and Colored Rosecomb Dorkings
Poultry breeders, seeing the almost inadvertent uniformity brought by the first (livestock) process, have often targeted superficial phenotypic uniformity without necessarily including the steps of foundation, isolation, and selection. In many cases poultry breeders have envisioned a final external phenotype, and then have blended various influences to attain that phenotype. In many poultry breeds the result has been that varieties within the breeds do not share histories of foundation, isolation, and selection with one another. For example, White, Buff, and Partridge Chantecler chickens each come from a different foundation, even though the final products resemble one another in all but color. Selection is the key here, with foundation and isolation playing minor roles if any at all.

Gina Bisco's White Chantecler
This second path to breed development leads, in poultry, to a logical split in what might be called primary breeds as opposed to secondary breeds. Primary breeds are those that are breeds in the livestock sense, having a background of foundation, isolation, and selection. Secondary breeds end up with their uniformity coming from targeted selection for a specific phenotype even though the foundation and isolation steps are not shared. Each of these types of breeds has importance, but they are fundamentally different in their function as biological units.

Many poultry breeders consider the outward phenotypic uniformity to be all that there is to breeds. In that case, outcrossing to bring things in is perfectly logical, because the breed is indeed (in their minds) that final external phenotypic package. This does change the underlying genetic package of the breed, which is of conservation importance. A good example are the multitude of Wyandotte varieties, many of which share no common foundation but which have an array of skin color, comb type, and body shape that is shared across them all. The superficial similarities are a veneer over very real underlying differences.

Unfortunately this attitude, and these practices, put at risk the many poultry breeds that are indeed primary breeds. These genetic packages must be protected. In these primary breeds, genetic phenomena like epistasis and linkage are important, and outcrossing can disrupt these.

Commercial Poultry made the White Crested Black Polish its cover bird in 1910.
Poultry breeders need to be diligent in understanding the character of their breeds, and need to reflect on the importance of foundation and isolation in maintaining the genetic uniqueness of their breeds. Ignoring this, and resorting to outcrosses, can assure that the result is “such and such” a breed in name only, with the underlying genetic package based on foundation and isolation long gone.

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