Can DNA tests tell how many chickens find their way into one McNugget?
March 1, 2012 6:27 AM   Subscribe

Could DNA testing theoretically be employed to determine how many distinct chickens found their way into one Chicken McNugget?

Also, how much time, effort, and resources might such an experiment take? (Any bets out there on how many chickens are "represented" by the average nugget?)
posted by duffell to Science & Nature (14 answers total) 4 users marked this as a favorite
The fact that chicken McNuggets are cooked would be a huge limiting factor - heat denatures DNA. Also, it depends on how similar the chickens are to each other - I could imagine the chickens that McDonalds uses could be inbred, which would make finding polymorphisms (differences in the DNA between individuals) difficult.
posted by fermezporte at 6:35 AM on March 1, 2012

No. You're sampling, at best. So, how would you know you'd got all the contibutors of DNA?
Also, some chickens contain more than one set of DNA.
posted by blue_wardrobe at 7:00 AM on March 1, 2012 [1 favorite]

Best answer: The chicken genome has be sequenced, which would help.

I can't think of a way in which you could get anything like an actual absolute number, but if you manage to convince a McDonalds employee to give you a raw chicken McNugget you could probably generate a decent 'over X many chickens in a nugget' kind of number.

You would need to spend a while bunch of time looking at the chicken genome for a series of hypervariable regions each flanked by conserved regions. You would then order primers specific to those conserved regions online to do PCR [helpful animation], which you could use to amplify those hypervariable regions in a way non-specific to individual chickens. You would then clean up the PCR product with a kit you would order online and then mail it of to a sequencing facility. You could then look at the sequencing results, pick apart how many distinct chicken sequences you think are in there, and produce a minimum number of chickens present per gram of nugget.

You would need to show that your hypervariable region was conserved within an individual chicken, to make sure you arn't counting chickens twice, and it would help if you were using already annotated regions. However you could do this with a couple chicken carcasses from the store and some time.

In a lab, this would all be a couple hundred bucks worth of primers at most, a few thousand worth of sequencing depending on how many runs you needed and how big of a batch of runs you could produce at a time, and a few hundred bucks worth of reagents. At home it would require a thermocycler, which I'm told can now be acquired for under a grand, a microcentrifuge unless you can get your sequencing facility to clean up your products for you, a gel box to electroporate your PCR products so you know your sending something real off to sequencing (which involves ETHIDIUM BROMIDE unless you're rich)

On preview, modern chicken facilities would discard gender bending chicks, but wouldn't be able to discard all of the healthy dimorphic chicks. This could only ever be a ballpark kind of number anyway.
posted by Blasdelb at 7:09 AM on March 1, 2012 [3 favorites]

Also, to do such a project as well as possible, it should take a good graduate student 2-3 months and probably would take them 6-9.
posted by Blasdelb at 7:11 AM on March 1, 2012

tl;dr -Your question is about DNA testing. I've gone and answered a question about McDonalds.

Slightly tangentially... the "Cows in a burger" trope is address by McDonalds UK on their Q&A[*] site.
  • how many cows make a burger?
  • Like burgers and mince from other large food companies or your local butcher, there might be beef from more than one animal in McDonald's hamburger patties. Let's get this in perspective - there is milk from more than one cow in a carton of milk and juice from more than one orange in a carton of orange juice. The key point here is that all the meat we use is great quality. The company source from over 16,000 British and Irish farms, all producing to the same industry leading standards.
And a follow-up:
  • No, these are not straight answers. People keep asking how many cows go into one burger and there is the same generic response, like an advertisement. HOW MANY COWS ARE IN ONE BURGER?? Give me a number, NOT A GENERIC RESPONSE. Obviously you are trying to avoid the question by diverting the topic to orange juice.
  • McDonald's is not trying to evade a direct answer and is sorry that you feel that this is the case; the reference to orange juice and milk was simply used for illustrative purposes. Beef is delivered from the approved abattoirs in bulk and will be made up a forequarter and flank cuts from a number of beef animals. Therefore, it is impossible to answer the question precisely. In the same way, if you buy a multi-pack of chicken pieces or a pack of mince in your local supermarket, then these will be sourced from any number of animals and packaged as one.
Unfortunately I can't find any similar questions asking them how many chicken's make up a nugget. Their answer, however, would have presumably been similarly vague and not DNA backed.

Is the question purely based on curiosity? Or some distrust of multiple-animal-munchies? Because if its the latter then you're never going to know and should avoid all minced meats that you didn't prepare yourself. McDonalds (UK) sell Chicken Selects which are "100% Whole Muscle" (ie not minced), but these are approx twice the price by weight.

If you want some real hilarity and a hearty does of crazy on the side have a look on that Q&A site for questions about milkshakes. Some properly insane questions... trying the weed the jokes from the crazy is an interesting experiment.

Oh did you want an answer and not a ramble? 3. There are 3 chickens in your nugget.[+]

[*] Note this is the UK site and the UK and US McDonalds may very different ingredient sourcing ideologies. For example - the UK chain has been using free-range eggs since 1997, sources all beef from Uk & Ireland farms meeting pretty stringent tests and (some of) those farms are open to the public annually for customer visits. There are a large number small (grass based) farms, versus the American supplier model of smaller numbers of large (feed based) farms. Yeah, yeah, PR and hype... but there does seem to be a lot more spin on quality and a lot less on price.

[+] This is a reply to your invitation for bets, not your invitation for facts.
posted by samworm at 7:11 AM on March 1, 2012

but if you manage to convince a McDonalds employee to give you a raw chicken McNugget

Are the McNuggets delivered raw to the store or partially cooked?
posted by Confess, Fletch at 7:13 AM on March 1, 2012

Plus - McD's make reference to McNuggest containing chicken stock. If this is the case then you'd have to expect it to be a huge source of potential contamination from other chickens. (Heat degradation of DNA arm-waved away etc)
posted by samworm at 7:16 AM on March 1, 2012

There may not be as much chicken meat in there as you think, either - much of the McNugget is corn or corn-derived.
posted by jquinby at 7:32 AM on March 1, 2012

And um, how many cows and pigs might be involved? BBC link, Guardian link.
posted by likeso at 8:09 AM on March 1, 2012

Best answer: In human DNA testing, we can only determine a minimum number of contributors to a mixture - i.e. if you detect four types at a certain locus, then you know DNA from at least two people is present (since one person has either 1 or 2 types depending on inheritance), but it's also possible that 3 or 4 or 12 people who have some combination of those types are present. With mitochondrial or Y-chromosome testing, you may detect just one profile, but any number of people from that maternal or paternal line could be present. I imagine results would be similar for your chicken testing.
posted by Flannery Culp at 8:35 AM on March 1, 2012

Complicating this might be the high degree of inbreeding in livestock, making it more likely that meat in a given batch might come from multiple siblings or cousins within a population with low variance. Also, I suspect that most meat products in this case are tagged with a serial number that allows for the franchise to identify the processing plants and farms it came from in case there's a need for a recall. The packing plant can usually tell you how many chickens go into the processor at a time.

However, it looks like there's a growing interest in genetic testing to identify the distribution of bushmeat and illegal fishing (paywall pdf). I've also read of DNA fingerprints used in drug enforcement to identify the distribution of marijuana strains, so it's not farfetched.
posted by CBrachyrhynchos at 8:52 AM on March 1, 2012

My guess is 1. If you think about it, there is more than enough chicken parts in a single chicken to make several nuggets. Although I'm sure the machines that do the grinding and forming probably work on a huge scale, there is really no reason to spend much energy intermixing the chicken parts. I'm sure there is a chicken slurry involved at some point in the process, but what benefit would they have in significant mixing of this slurry.

To say this another way, one batch of nuggets might take 1000 chickens, but there is no reason to assume the processing involved will distribute the parts from these chickens into lots of nuggets. At least there would seem to be no benefit to the producer, but it clearly would take extra work to achieve...
posted by NoDef at 9:25 AM on March 1, 2012

Response by poster: Big thanks to everyone for your responses. This was mostly a "Just out of curiosity..." question. This morning I was toying with the idea of a "Kickstarter Lab" where individuals could propose/debate/vote on--and eventually pledge money toward--specific lab projects to be taken on by a dedicated team. Projects might have as narrow a focus as this one (and potentially be just as asinine), or perhaps be broader and further-reaching.

This is not to say that such a thing would make ANY sense outside of my own mind, but in my imagination at least, this could be a way for everyday people to engage with the research process and track its outcomes. Discovering the number of chickens who contribute to the average nugget is just one of those everyday "Hey, I never thought of it that way" things: not a useful piece of knowledge in and of itself, but in terms of introducing John Q. Public to the joys of discovery, this is the sort of thought-experiment-made-reality that might be interesting. Granted, the whole chicken nugget DNA thing sounds as though it would be difficult if not impossible to determine in a lab through contemporary methods/technology.

(Since this morning I have learned of BioCurious, which is not exactly the model I was mulling, but is a fascinating project.)
posted by duffell at 11:16 AM on March 1, 2012

Kickstarter for science: RocketHub
posted by momus_window at 1:10 PM on March 1, 2012 [1 favorite]

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