Edemas (Swellings) & Grasspersil grass affected!

You may be wondering how on earth grass could cause swellings. Swellings called ‘Edemas’ which are due to fluid becoming trapped within various tissues.

Because gravity causes fluid to follow the path of least resistance, edemas usually occur in the legs, under-belly and/or sheath. Sometimes they can be observed in odd places like the cheeks (‘chipmunk cheeks’).

Note we are not talking here about swellings associated with injuries. Also be aware that some edemas are potentially life threatening, if they are not resolved within a few days, call the vet!


Overview of Grass Related Edemas

Did you know that the reason the ‘Crest’ of the neck suddenly goes rock hard is because it has filled up with fluid? This is grass related too and coincides with relatively sudden changes in the grass after rain and with the season, in horses already showing signs of ‘Equine Metabolic Syndrome’ who already have the ‘cresty’ neck.

Geldings will often get a swollen sheath and some horses and ponies will develop a ‘ventral edema’ as in the picture. They are frequently closely associated with either current or impending laminitic episodes. (It is very interesting that the digital cushion within the hoof capsule is made of the same sort of tissue as the crest of the neck).

Grass related edemas are caused by low protein levels in the blood (particularly albumin) which precipitates the peripheral capillaries leaking fluid. This is a downstream effect of high potassium in the diet from the changes in the grass.

‘Grass related’ edemas will be the same temperature as the non-swollen, surrounding tissues and are not painful to touch. Apart from the crest of the neck they will usually be ‘pitting’, meaning if you press your thumb on them the indentation will stay there after you remove it. They are not ‘inflammatory’ swellings which would be hot and painful.


Other types of swellings...

‘Lymphedema’ is also characterized by swelling but is a more serious long-term condition where a blockage of the lymphatic system causes excess fluid to collect in tissues resulting in swelling of the limbs. This develops more slowly whereas ‘grass-related’ edemas appear quickly and generally resolve quite easily.

Another form of swelling is ‘Stocking Up’ which is obviously not a grass related issue as it occurs when the horse is confined to a small area such as a stable, which means he is inactive. Constant motion serves as an integral part of the circulatory system, ensuring that fluids are pumped back up the limbs. Horses stock up in hind limbs because these are furthest away from the heart.