Read Dr. Epsy, AAEP(equine reproductive specialist) Comments of
Myth to regular sheath cleaning.
http://www.aaep.org/info/horse-health?publication=819
Summary:
What looks like dirt is natural accumulation. Horses in wild never have sheaths cleaned.
We've never had a problem with swollen sheath in any gelding until I read an old book that states to regularly clean it. So, I cleaned it out of guilt and Now my horse has a swollen sheath!
I agree with above vets that swollen sheath can arise from a number of factors. One seems to be from cleaning/disturbing via cleaning when not warranted. So check concerns with a vet first and remember: interior genitals maintain own natural environment that shouldn't be disturbed unless something goes amiss first. What looks like dirt-simply isn't. Instead its the very natural accumulation of oil and lubricant. Read the reproductive specialists comments and Disregard old books: Don't disturb to clean a penis/sheath that's functioning well. and never with a garden hose that may cause internal water damage.
Our welsh x had a big lump on his belly and a swollen sheath this month. My vet declined to give him dex due to the laminitis risk and just had me cold hose it. It went down slowly over about 2-3 weeks. It appeared to be a reaction to a spider bite or some other nasty bug.
What did they say at the equine hospital? One of my horses had a swollensheath this past month and we gave him Azium (Dexamethasone) and did a thorough cleaning. That seemed to take care of it, but I can say that the heat had a lot to do with how swollen it was. It has been so hot this summer that many horses' sheaths, legs, etc are swelling up.
My arab gets the same, his is an allergy to fly bites. Usually we can feel them and apply antihistermine to area. In a few days swellen goes down and back to normal