Udder edema is a metabolic problem affecting cows during early lactation. It is characterized by an accumulation of lymph-like fluid in the udder. Fluid begins to pool at the base of the udder and, in more severe cases, the entire udder is affected. In extreme cases, swelling will also occur in front of the udder, on the underside of the cow, and at the back of the udder toward the vulva.
Udder edema is not considered to be a major problem, but rather an inconvenience for dairy producers. In extreme cases, the swelling causes a shortening of the effective length of the teats and makes application of the milking machine difficult. It is also thought the extra weight of the accumulated fluid can place added stress on the suspensory system of the udder. Over time, stress on the suspensory system can lead to a breakdown of the udder, also known as pendulous udder.
Typically, udder edema begins shortly before calving when blood flow increases to the udder in preparation for lactation. It is normal for most cows to experience some degree of udder edema before calving. Under normal conditions, the edema will clear from the udder within a week or two post-calving. The goal for dairy producers is to control the severity of edema.
Another major problem that causes the udder to swell is mastitis. Swelling as a result of edema can be distinguished from other types of edema by using the
"fingerprint" test. The "fingerprint" test consists of pushing a finger gently into a swollen udder, and then with-drawing the finger. If the swelling is due to edema, an indentation or
"finger-print" will be left, whereas swelling caused by mastitis is very hard making it difficult to leave an indentation.
Treatments for edema include massage, exercise, or other methods to physically remove fluid from the udder. These methods of treatment are temporary and, therefore, not very effective. In extreme cases, treatment may involve the use of diuretics to reduce fluid retention. The best treatment for udder edema however, is prevention.
The primary cause of edema is salt (sodium chloride or NaCl) intake by the cow during the dry period. Salt causes fluid retention and increases the severity of edema. Prevention is best accomplished by restricting the amount of salt a dry cow receives. The salt requirement of a dry cow is only one ounce daily. It is not actually salt a cow requires, but sodium and chloride. When a typical forage program of grass hay and corn silage is fed to dry cows, most of the sodium and chloride needs are met.
Other factors have also been identified as causes of edema. Other salts, such as potassium chloride, can lead to udder edema. Feeding buffers, such as sodium bicarbonate, to dry cows can cause udder edema due to excess sodium intake. Some mycotoxins, such as zearalenone, can cause an edematous swelling of the udder. The use of BST has caused edema in some cows because of the increased blood flow to the udder. Also, genetically, some cows are more prone to edema.
The best way to prevent udder edema is to limit salt intake during the dry period. If udder edema is a problem in your herd, check the amount of salt dry cows receive and consult with a nutritionist.