OverviewThe sheath is at the farthest point from the heart and damage to the blood flow in castrated males can sometimes prevent the normal flow of blood leading to swelling (edema) of the sheath.
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In reply to the question left by Stephanie below – “I was wondering if it was something to do with the lymphatic system that the sheaths would get swollen… I see it on top show horses to back yard horses.. I also wondered if it was a precursor to Cushing’s disease? So any thoughts on why some have only one side edema? Thanks so much for the topic!”
Stefanie – Have you ever seen this on stallions? I have not unless they have been kicked in the sheath area but this usually resolves over time. I believe that there is collateral damage to the flow of blood, lymph or both from the castration surgery. Unfortunately I have no proof but a few observations:
The edema is never painful or hot (infection or inflammation).
The edema is often worse in colder months (less movement or vasoconstriction).
Exercise tends to reduce the edema (increased cardiac output plus movement pumping away fluid in the tissue).
The edema may be one sided or asymmetrical especially after the horse has been laying down.
The blood flow from the abdomen and the sheath area (and the udders of mares) to the heart returns caudally to the iliac veins of the hind legs then goes up to the vena cava to flow back to the heart. This long route requires good blood flow but if the vessels are damaged, then the fluid will escape into the surrounding tissue causing edema. This also occurs in pregnant mares as the heavy foal puts pressure on the same vessels. It is the reason why with increased blood flow (movement, warmth, foal delivery), the edema resolves.
Cushing’s disease is not associated with sheath edema. However in horses with “Metabolic Syndrome,” the sheath as well as other parts of the body will accumulate fat. The difference is that with fat, you cannot leave an impression of your finger when it is pressed into it whereas an impression is left in edema – hence the name “pitting edema.”
In my castrations there was one rule. All incisions heal from side to side, not end to end. In other words a short opening and a long opening both heal in the same amount of time. I would always make a long incision to adequately expose the testicles which would decrease the trauma to the surrounding tissues. My geldings to my knowledge rarely had post surgical swelling nor sheath edema long after the surgery. As you say, there is little research on this subject because there are no adverse side effects from sheath edema, just a curiosity.
PS – be sure to watch the video on sheath cleaning and let me know if you have anything to add. Thanks for commenting – Doc T
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