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Reverse Engineering Angus Indexes Part 2 - $QG & $YG

I posted a relationship between the carcass indexes last week and over the next few weeks I’ll be posting approximations for the other Angus index values.  I saw approximations because these are most certainly not the actual formulas themselves but rather reverse engineered approximations of them.

Speaking of data, those Angus guys don’t mess around on blocking IPs.  The story I’ve been told is they had a bunch of their data stolen/taken in bulk by another breed association quite a while back and ever since then they’ve made it annoying to find more than a few animal pedigrees.

I’m blocked on three now and I didn’t pull up more than a couple dozen bulls in any given session.  I respected their data policy and didn’t use bots, just looked up bulls at various ends of the spectrum for various EPDs and then pulled up more animals through their pedigrees.

Regardless, I put together a data set of about 100 bulls with a wide range of EPDs and ages and threw the info into Eureqa to see how they’re calculated.

$QG


This one is extremely straight forward when compared to the other $ indexes and it almost makes you wonder what the point of having an EPD for both marbling and quality grade is.

$QG = 5.05 + 54.16 * MARB - 17.97 * MARB ^ 2

You can use the MARC conversions to get an estimate of where your bull from another breed measures against his Angus counterparts quite easily.

Don't want to do that?

Don't worry, I've got a handy little tool coming soon.

$YG

While I analyzed the full EPD profiles for the 100+ Angus cattle used in this, the results for $YG came out exactly how you'd expect.  It's based on rib eye area, carcass weight, and fat.  There are signficantly more complicated formulas that would get a big closer than this but they're all based on those three traits.

X = 5.6 + 11.6 * RE - 0.17 * CW - 95.8 * Fat

$YG = -0.0171 * x2 + 1.2345 * x - 0.7187

The second part of that equation is due almost entirely to the animals on the extremes for $YG.  You'd have to ask the AAA why it works out that way.

There’s no MARC info for carcass weight so it wouldn’t be as straight forward to do a cross breed conversion.

Next week is $EN and $W approximations.

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