This can retard normal exchange of nutrients and metabolites. Filtration of the extracellular fluid exceeds drainage. Anything that causes increased capillary pressure, such as decreased plasma protein, increased capillary permeability or lymphatic blockage, can result in swelling and congestion of the extravascular compartment. Udder Edema is swelling of the udder and occurs particularly in first calf heifers at calving time. Fluid accumulates between skin and glandular tissue, as well as in the gland.
Severe edema can strain supportive structures of udder.
Udder edema is often caused by an imbalance of hydrostatic and osmotic pressures, increasing fluid flow out of the capillaries into the interstitial spaces. This may occur because of damage to the capillary walls or obstruction of the lymphatic system. Don't know exactly why it happens, but from human medicine, increased salt intake, increased fluid intake, increased environmental temperature and damaged innervation can contribute to edema.