PROCEDURE
Halter the horse. Holding the halter in the left hand, stand on the horse's left side. Use your right hand to find the location where the bulge of the masseter cheek muscle ties into the horizontal bone of the lower jaw.
Slide your hand back and forth along the sharp keel of jaw bone you feel there. You can see and feel a firm "noodle" the consistency of a cooked macaroni noodle. This is the "bundle" of vein, artery and nerve, that crosses over the bone obliquely.
Use your index finger to locate the thick, rubbery feeling artery, and gently press into it with the fingertip. If you feel nothing, then try gently reducing and increasing the pressure with your fingertip until you do.
If you have question about whether you are on it or not, then slide the fingertips forward and backward (cranial and caudal) on the edge of the bone, feeling for the crossing band of tissue. Once you feel a rhythmic pulse, count the number of pulses in 15 seconds and multiply by 4 for the total heart beats per minute.
TIPS FOR SAFETY AND SUCCESS
Either you or an assistant can hold the horse while you take the pulse. Use your index finger to locate the artery, gently press into it with the tip of your index finger, which is your most sensitive finger. Be patient. The vessel may be harder to find in horses with thicker necks, dense hair or more fat.
The strength of the pulse can be hard to assess without lots of practice, and also can be quite variable depending upon the above factors.
When assessing fitness, consider that in most fit horses, the pulse drops to about 70 BPM about 10 minutes after intense exercise. It typically drops below 60 BPM after moderate exercise.