Page 735 - The Veterinary Care of the Horse

The lymphatic system plays a vital role in removing inflammatory products from injured

or infected sites. The fluid is filtered by the lymph nodes (glands) along the course of the
VetBooks.ir larger vessels before draining into the bloodstream. These can become swollen and painful or
form abscesses in the presence of infection.

Conditions of the lymphatic system

OEDEMA AND FILLED LEGS

Most of the time, the production of tissue fluid and the drainage of lymph are kept in balance.
However, if for any reason the flow of lymph slows down, the tissues become swollen with

accumulated tissue fluid. This is known as oedema. Oedematous tissues are not normally hot
or inflamed, but if pressed firmly with a finger a deep impression of the finger (or ‘pit’)

remains for some time.
Oedema can be caused by the following.

• Obstruction to the flow of blood in the veins. This can be localized due to an injury or

generalized if the horse is in heart failure.
• Obstruction to the flow of lymph in the vessels.

• Reduced levels of protein in the blood so there is insufficient osmotic pressure to draw

the tissue fluid back into the blood vessels. This can occur with severe kidney, liver or
gut disease or as a result of severe parasitic problems.

• Restricted exercise. In the horse, the tissue fluid in the lower limbs may accumulate if
there is insufficient activity to massage the flow of lymph back to the heart against the

pull of gravity. This is why some horses develop filled legs at night when they are stabled
(Figure 16.5). This can be exacerbated by overfeeding of concentrates which interferes
with the protein and electrolyte balance. The filling is more common in the hind limbs,

but the front legs may also be affected. The lower limb becomes rounded in shape and
the definition between the tendons and the suspensory ligament is lost. The swelling is

not painful but may cause stiffness at the start of exercise. Both the swelling and the
stiffness usually resolve within a few minutes when the horse begins to move. The

condition can be managed by turning the horse out for longer periods and by applying
stable bandages when the horse comes in.