GENEWATCH
 
EDITOR'S NOTE: THE MODERN CHICKEN'S FAMILY TREE
By Samuel W. Anderson
 

This issue brought up a few "worlds colliding" moments for me, but in a good way. When I'm not editing GeneWatch, I work at a nonprofit called New Entry Sustainable Farming Project, where I'm the livestock and poultry guy. I also grew up on a sheep farm, and across the twenty-plus years my dad has been keeping detailed records on each ewe and lamb, I have seen firsthand the subtle but remarkable effects of selective breeding.

A couple of years ago, through my work at New Entry, I had the privilege of attending the International Poultry Exposition in Atlanta. It's the largest poultry industry event in the world, and I do mean "industry" - these are the guys in business suits, not Carhartts. I already knew that most conventional poultry farmers-particularly the ones who raise meat chickens, or "broilers" - don't end up making much money for their increasingly limited role in the poultry supply chain; but the gaudiness of the industry booths (three-story chicken-shaped displays, open bars galore, that sort of thing) said very clearly that someone was making money. A typical broiler spends all but two or three days of its life under the care of a farmer, who has signed a contract with Tyson or Perdue or Pilgrim's Pride to shelter and feed the birds from when they arrive as day-old chicks until the company sends a crew to take them to the processing plant at five or six weeks. But all the real action happens before and after that.  I could go on for pages about the "after" (seriously, send me an email if you really want to hear about it), but what concerns us in this issue of GeneWatch, since we are examining the role of genetic technologies and research in agriculture, is the "before."

The vast majority of broilers in the U.S. come from just four poultry genetics companies, all of which were attempting to make a splash at the International Poultry Expo. Each of their extravagant displays featured information about the company's genetic offerings, different broiler pedigrees which are supposed to be tailored to meet subtle differences in demand by the hatcheries and the vertically-integrated poultry companies that bring the birds to market. Aviagen is the largest of the broiler companies, yet it offers just a handful of pedigree lines: Indian River, Arbor Acres Plus, Ross 308, Ross 708 and Ross PM3. Aviagen had made glossy one-pagers for each brand, each with a photograph of that variety's clean white spokeschicken and a list of its "specs"-what size it will be at different ages, how much feed it will need to get there, and figures denoting flock uniformity. Uniformity struck me as an especially ironic figure. I know why it's there-uniformity is a virtue in the broiler industry largely because it suits the extraordinary amount of mechanization, from incubation to processing-but it's a funny thing to say one brand is especially uniform when the photographs on all five flyers looked very much like pictures of one chicken from five slightly different angles. The differences in their stats-or, rather, the minuteness of those differences-was even more striking. At 35 days (around slaughter time), the Ross 308 is 4.96 lbs, having eaten 7.77 lbs of feed, while the Ross 708 is 4.71 lbs, eating 7.26 lbs of feed.1 So the Ross 708 converts feed more efficiently - a whopping 1.6% more efficiently, to be exact.

The incredible uniformity of broilers derives from their pyramid-shaped family tree. At the bottom of the pyramid is a hybrid bird (billions of them, actually) which, thanks to hybrid vigor, is an even better meat bird than either of its parent lines; however, if you were to cross two of the hybrid meat birds with each other, that hybrid vigor would be lost in the next generation. These are end-of-the-line chickens, created only for meat and not for passing on their genetics-what in other types of livestock breeding you would call a "terminal cross."

In order to create this hybrid vigor, you need distinct male and female parent lines. Males are selected for growth rate, edible meat yield, and feed conversion ratio, all traits that make them efficient for meat production; females are selected for those traits too, and also for egg production, which makes them a more attractive buy for hatcheries. Some of the parent stock may also be hybrids, carefully selected to combine traits that fit (or "nick," in industry language) with each other and with the opposite parent's line. Hatcheries buy parent stock from genetic companies, which guard the grandparent and great-grandparent genetics. The top of the pyramid - the great-great-grandparents of the birds that will end up as chicken nuggets - are the "pureline" pedigrees. In 1998, the genetics of the world's 400 billion Cornish Cross broilers could be traced back to 400,000 individual birds from just 35 to 40 purelines. In other words, for every one million meat birds, there is one common great-great-grandparent.

The following articles tackle the broad topic of "genetics in agriculture" from different angles, from agricultural biodiversity to transgenic technologies, from research priorities to consumer activism. There will be plenty of discussion about genetically modified crops, but even if that is where your passions lie - in fact, especially if that is where your passions lie - I hope you will read further. There is plenty to say about GMOs, but the role of genetics in shaping the plants and animals that feed us goes much, much deeper.

 

 

1. http://www.poultryhub.org/wp-content/uploads/2012/06/Ross308BroilerPerfObj2012R1.pdf; http://en.aviagen.com/assets/Tech_Center/Ross_Broiler/Ross708BroilerPerfObj2012R1.pdf

 
 
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