Dear Dr. Vittoria: I have noticed an unusual lump in a rather private area on my gelding when he urinates. I thought I saw something like this last year, but it seemed to go away. Not that I'm watching when he urinates, but it caught my eye. I'm wondering if I should be concerned. - Mike in Myerstown

Dear Mike: Any lumps in an animal's private area should be examined further. It is not unusual for an owner to notice abnormalities in the nether regions of their horses. Often you are going about your normal business and all of a sudden it is just hanging out in front of you. That is the prime time to examine an area you don't normally get to see. This is an effective way to discover problems while they are small.

Gelding owners often have their vet clean the sheath area while the horse is getting his annual dental exam and floating. We can explore the nether regions where you may not have dared to go. This helps us establish a baseline of what is normal for your horse and to document any lumps that were not there before.

If you are cleaning your horse's sheath on your own, make sure you have a vet check your technique. If you are not getting all the way to the end of it and removing the waxy substance (smegma) that builds up in the urethral recess, then you may not be examining the whole apparatus.

There are a few cancers that like to grow in this area and can be quite aggressive. Squamous cell carcinoma will develop right at the end of the horse's penis. It is often not something people notice since horses can be quite shy about letting you see it all. There are the occasional exhibitionist horses who have no problem showing the world what God gave them. You can be happy if this is your gelding.

Melanoma is another common cancer that can affect horses in their private areas. Just like in people, melanoma is a cancer of the pigment cells of the skin. However, in humans it is linked to sun exposure, but not so in horses.

We typically see equine melanoma in areas where the sun never shines. They usually start as small, M&M-sized lumps just under the skin. They can progress over time into open ulcerated lumps that cause infection along with inflammation.

If you are lucky, your gelding may just be suffering from nothing more than poor hygiene.

Geldings need to be cleaned annually to make sure the wax doesn't get too thick. These wax globs can stick to the sides of his shaft and appear to be cancerous growths. That may explain their mysterious appearance and disappearance.

You should get a professional horse-boy-part washer, aka a vet, to look at him just to be sure.

Christina Vittoria, D.V.M., practices equine, small ruminant, and companion animal medicine at Willow Creek Veterinary Center. Comments offered here are for educational purposes only. Readers should consult their veterinarian before taking action. Have a question for Dr. Vittoria? Send it to Please put ASK THE VET in the subject line.