Something’s Missing Here: Explaining Ridglings

Honor Code made the news last weekend both for his racing performance and for a medical condition. Trainer Shug McGaughey announced that Lane's End Racing's Grade 2 Remsen winner would get some time off following surgery for cryptorchidism, but he isn't the first graded stakes winner to go under the knife for the condition.

Experts estimate a small minority of male horses have one testicle that fails to descend at puberty, making them cryptorchids or ridglings. Many suspect that the condition may have a genetic link, although that has not been proven. Several horses in the Seattle Slew line have come up with the condition, including Honor Code's sire, Lane's End born and raised A.P. Indy, along with Slew o' Gold, Dahar, Gray Slewpy, Freedom Child, Nates Mineshaft, as well as Summer Squall, half-brother to A.P. Indy.

The reason for cryptorchidism is unknown, but the condition is usually apparent by the time the horse is around 16 months of age. In normal colts, testicles travel from the abdomen down the inguinal canal to the scrotum. In the case of a ridgling, the undescended testicle may stay in the horse's abdominal cavity, or drop partially down the inguinal canal and become caught behind a structure called the external inguinal ring, which surrounds the exit of the canal.

Sperm cannot survive in the increased temperature they are exposed to next to the body, so undescended testicles are nearly always non-functional in terms of sperm production and are usually undersized.

Experts agree that cryptorchidism is relatively uncommon, although it is difficult to guess what percentage of horses are affected by it on average. Just one horse in this year's Keeneland September Yearling Sale was cataloged as a ridgling, compared to 2,032 colts.

The timing of puberty can coincide with a horse's sale as a yearling or 2-year-old, making the examination of reproductive organs part of the usual pre-purchase check for high-priced weanling or yearling prospects.

Rood and Riddle Equine Hospital ambulatory veterinarian Dr. Scott Pierce said it can sometimes be challenging to classify a young horse if it has testicles that have descended into the inguinal canal but have not yet passed the external inguinal ring.

“You have to read the conditions of sale,” said Pierce. “Basically, if you can palpate the testicle in its entirety through the external inguinal ring (they can go through as colts) but that doesn't mean they'll be successful colts. A lot of those testicles (that are detectable but haven't dropped as yearlings) are going to be no good.”

The external inguinal ring eventually thickens to less than one centimeter in diameter as the horse ages, which means a ridgling whose retained testicle is still in the abdomen after he has passed puberty can't be expected to drop it spontaneously later in life.

Since the emergence of well-known sires like A.P. Indy who are ridglings, Pierce says he doesn't believe the status has any substantial impact on a horse's potential stud value in today's market.

Many horsemen believe that the undescended testicle has the potential to cause discomfort, especially on the racetrack.

“They're up there, they're never going to be functional. Maybe they bother them, maybe they don't; I think it's a prudent thing to do to get them out,” said Mike Cline, general manager of Lane's End Farm, where A. P. Indy stood his entire career.

Veterinarians say that, although the condition sounds uncomfortable to us, there's little scientific reason to think the horse is actually in pain as a result.

“There's the concern that that can be a problem, but personally I don't think so,” said Dr. Brett Woodie, veterinary surgeon at Rood and Riddle Equine Hospital. “There's no tension on it if it's abdominally retained. There's unfortunately no way to know.”

Woodie says that many managers choose to have the retained testicle removed, just in case. In most instances, the remaining, descended testicle is fully functional and the horse can still be bred.

Cline says in his experience the remaining testicle often becomes enlarged and, as a result, stallions are able to keep up with the standard daily breeding schedule without a problem.

“With Gulch, we removed his testicle after he got here, and he had a bump in fertility, so I think oftentimes it helps,” said Cline.

The surgery to remove an undescended testicle is minimally invasive, with little risk as surgeries go, according to Woodie. Depending on its location, surgeons may remove the retained organ via small incisions or via laparoscopy, which uses a thin, lighted tube to examine and remove the testicle. In some cases, owners may use the surgery as an opportunity to geld the horse entirely, as was the case with 2003 Kentucky Derby winner Funny Cide.

The incision is typically sewn with absorbable sutures to keep post-operative care easy.

“The care basically consists of observation and monitoring body temperature, but you're not going to be up there taking sutures out. That wouldn't be fun for anybody,” said Woodie.

Some ridglings are said to have undergone performance or personality makeovers after their surgeries. A.P. Indy had his surgery after his first start in 1991, and subsequently embarked on a win streak that included the Grade 1 Hollywood Futurity, Grade 1 Santa Anita Derby, and Grade 1 Belmont Stakes.

“I think there's plenty of talk about ridglings being more studdish than horses with two fully-descended testicles. I think that's a viable point,” said Cline. “I remember Summer Squall was a bit of a handful before we took his testicle out. But A.P. Indy on the other hand, you would have never known, he has such a good disposition.

“Honor Code, you definitely would have never known [he was a ridgling]. He's not studdish, very quiet to be around.”

According to McGaughey, Honor Code is expected to recover in plenty of time to contend two prep races on the road to the Kentucky Derby. The ridgling's connections will doubtlessly be hoping that he bounces back from the operation as well as his sire did 22 years ago.