The lymphatic system in mammals is the centre of the body's immune system. The factories of the system are the lymph nodes. If the lymph nodes are swollen, it is usually a sign of some type of illness or infection. If you own horses, spotting swollen lymph nodes may be the first sign that you should take your horse to a vet. Since the animal can't tell you something is wrong, knowing what swelling in the lymph nodes looks like is important.

Observe the horse's stance. Horses with swollen lymph nodes often stand with their necks outstretched, to relieve pressure in the neck area.

Look in the lymph node area on a horse's body. The lymph nodes on a horse are located behind the jaw -- on the throat latch area of the neck -- over the eye sockets -- in the chest area, and the abdominal cavity. Swollen lymph nodes may appear round and hard. The horse may flinch when you touch them.

Take the horse's temperature using a rectal thermometer. The normal range of body temperature for a horse is between 37.2 and 38.3 degrees Celsius. Temperatures higher than this may indicate an infection.