All horses have them. A feathered whorl down each side of the chest above the front legs.
Usually the pectoral whorls are even. Either both reaching high into the chest or both short and compact. The breed, type, and movement of the horse reflected in the hair.
Sometimes that isn’t the case. Occasionally the whorls will be uneven, one higher than the other. When this happens there will be a leg preference. The horse will want to reach farther with the leg that has the higher whorls. This will be the preferred lead.
What other consequences can it have?
It goes without saying, but still needs to be drilled into our heads, the entire body is connected. When there is something going on in one place it affects all the other body parts.
When a horse is out of balance in the front legs, what does it do through the rest of the body?
The first thing we would do is check the underside of the jaw and belly to see what those whorls look like. If they are even the effects will be less. If those whorls are uneven too, the whole body will be working against itself. The crookedness having far reaching consequences.
The higher pectoral whorl shows a stronger front leg. That strength and preference is echoed in the opposite hind leg. With these two legs being strongest, the hind leg opposite the low whorl will be weaker. Between overloading the front leg with the lower whorl because they like to use and reach with the leg with the higher whorl, and overloading that front leg because the corresponding hind leg is weaker, the leg with the lower whorl is more likely to be injured. This can range in severity from tendon and other soft tissue injuries to uneven hoof angles, hi/low syndrome.
The connections through the entire body are so strong that any unevenness ricochets from the chest through the hind quarters then back to the front legs. Little thing,s like a slightly stronger front leg, can have far reaching effects.