L

laminae: a part of the hoof. See insensitive laminae and sensitive
      laminae. 

 laminitis: an inflammation of the sensitive laminae of the foot. Many
      factors are involved, including changes in the blood flow through the
      capillaries of the foot. Causes include ingesting toxic levels of grain,
      eating lush grass, systemic disease problems, high temperature, toxemia,
      retained placenta, excessive weight-bearing as occurs when the opposite
      limb is injured, and the administration of some drugs. Laminitis usually
      manifests itself in the front feet, develops rapidly, and is life
      threatening, although in mild cases a horse can resume a certain amount of
      athletic activity. Laminitis caused the death of Secretariat.

laser (or cold laser): a low-intensity focused beam of light used to
      reduce inflammation and promote circulation.
     

lateral: toward the side and farther from the center. Pertains to a side.
     

lathered (up): see washed out.
     

lead: 1) see shank. 2) the front leg that is last to hit the ground during
      a gallop or canter stride.
     

left laryngeal hemiparesis: when the vocal fold or arytenoids cartilage on
      the left side of the airway becomes partially or totally paralyzed and
      interferes with air flow. Causes a whistling or "roaring" noise during
      inspiration when the horse exercises. See roaring.
     

ligament: a band of fibrous tissue connecting bones that supports and
      strengthens the joint and limits the range of motion.
     

lunge: a method of exercising a horse on a tether ("lunge line").
     

Lyme disease: infection with the spiral-shaped bacteria Borrelia
      burgdorferi, spread by the bite of an infected tick. Signs may vary widely
      and can include recurrent lameness that shifts from one leg to another and
      for which no other cause can be found, arthritis, stiffness and reluctance
      to move. Treatment is usually administration of antibiotics from the
      penicillin or tetracycline family.