In this month’s installment of Conformation Insights, “Developing an Eye for the Total Hind Limb,” Deb Bennett, PhD, describes how to evaluate the horse’s hind limb structure. Here are the measurements and equations you need to better understand her calculations and to make your own.

To Calculate Total Hind limb Length

1. Going from point-center to point-center, measure the lines representing the femur, gaskin, hind cannon, and pastern + hoof segments of the hind limb (black lines in all illustrations).
2. Add these lengths and write down the total (this is the total hind limb length or THL).
3. Multiply THL X 100.
4. Measure the standing height of the hip socket (green line). The green line must be perpendicular to a line connecting the toes of the feet on either the left or right side of the horse.
5. Divide the number you found in step 4 into the number from step 3.

Here’s an example based on the analysis for this month’s Horse no. 3:

1. Femur segment length: 2.549 units (“units” are the arbitrary units produced by my computer software; it’s fine to measure in millimeters or sixteenths of an inch, and the percentages will come out the same. Just be sure that you make all measurements in the same units).

Gaskin segment length: 2.637

Cannon segment length: 2.255

Hind pastern + hoof segment: 1.187

2. Total hind limb length: 8.628

3. Total hind limb length X 100 = 862.8

4. Standing height of hip socket (length of green line): 8.213

5. 862.8 / 8.213 = 105.05, round to nearest whole number = 105%

To Calculate Percentage Straightness

This represents an application of a principle of geometry or trigonometry to conformation study. In calculating percentage straightness of the stifle joint, we are comparing its actual measured angle to 180 degrees – the angle the same joint would have if it were straightened out completely or “100% straight”. We can calculate this separately for stifle and hock joints, then average the two to find the “percentage straightness” of the hind limb above the ankle. Alternatively, do this:

1. Measure the stifle angle (I consider that the only good way to do this is on the computer; both hand-measurement with a protractor of an enlarged photo, and direct measurement of the live horse with an angular goniometer, are rather inaccurate).
2. Measure the angle at the hock.
3. Sum the measurements.
4. Multiply this sum X 100.
5. Divide by 360 (360 represents 360 degrees, i.e. 180 degrees for each angle measured).

Here’s an example based on the analysis for this month’s Horse no. 3:

1. Stifle angle = 152 degrees
2. Hock angle = 155 degrees
3. Total of both angles = 307 degrees
4. 307 X 100 = 30700
5. 30700 / 360 = 85.27, round to nearest whole = 85% of perfectly straight