By Ben Espy, DVM, DACT

Question: I am concerned about the abnormal smegma buildup on my 17-year-old palomino gelding’s sheath. Since we purchased him, we have noticed that when he extends, there is crusty buildup all over him. We began cleaning him and have been doing so about once a month for the past three years because within 4 weeks, he is crusty and dirty again. We use a particular brand of Sheath cleaner about every six months and use regular Vaseline or baby oil in between times since we do not want to use harsh cleaners each time and so often. 

Everything I have read says that you do not clean them this much and nothing I have read tells me why this horse has this abnormal build up. I am at a loss as to what to do about this. We think he may be proud cut, but could that have anything to do with it? I also own a stallion, which he only needs to be cleaned once every six months. 

There is also a raised red area on the sheath. What might this be? Could it have something to do with the buildup? 

Answer: This is a great question. The amount of what we call normal smegma varies greatly from horse to horse. Not only does the amount vary but the quality/texture of the smegma will vary as well. Some horses will have dry and scaly smegma residue on their penis shaft while many others will have moist and sometimes offensively smelling smegma in their prepuce and on the penis.

My first recommendation is to first seek the advice of a theriogenologist (animal reproduction specialist) that can identify normal and abnormal parameters for you. You can search for a veterinarian who has a special interest in reproduction at www.therio.org and you can search for someone who is board certified in theriogenology at www.theriogenology.org. AAEP also has a veterinarian locator service (www.aaep.org/dvmsearch), which can provide you with local members that may be specialized in theriogenology.

I admire your desire to provide for this horse, but also must caution you to be careful in providing "too much care". Washing a gelding 36 times in three years is most likely destroying all of the normal and protective bacteria on the penis. Even with soap made for the sheath, washing to death of the normal "microflora" will allow the resurgence of inappropriate and pathogenic bacteria.

I always remind people that wild horses will live 20 years or more and never have their sheath/penis washed or a "bean" removed.

The term "proud cut" is usually misused. It has been reported by multiple authors in published research data that 65 to 80 percent of stallion behavior is learned behavior. In other words, even if he's properly castrated, he is most likely misbehaving because of training issues, not because he has testosterone issues from a portion of a testicle left in him. You can easily determine by blood tests whether the horse has testicular tissue left in him.

Castrated horses, intact horses and improperly castrated horses all have similar amounts of smegma.

Three common skin tumors that can appear as raised nodules on the shaft of a penis are Squamous Cell Carcinoma (SCC), sarcoids (the most common skin tumor in horses), and "coital exanthema", which is caused by the Herpesvirus and can be spread via live breeding.

My question in this horse might be whether the nodular/vesicular skin appearance might have been exacerbated by aggressive washing that may have induced a mild chemical irritation. Your veterinarian could sedate the horse, infuse local anesthesia proximal to the lesion and then acquire a punch biopsy through one of the characteristic lesions you are worried about.

Ben Espy, DVM, DACT, San Antonio, Texas.

Reviewed by original author in 2016.