Cryptorchidism in the horse

Introduction

When one or both testicles (testes) are not descended in the scrotum, the horse is called a rig, ridgling, or cryptorchid. Cryptorchidism is a developmental defect in both animals and humans. It is important in the horse because: the retained testis does not produce fertile sperm but does produce testosterone which gives the stallion its behavioural characteristics; cryptorchid testes are more prone to developing tumors compared to descended testes and the cost of castration is increased.

During the fetal life, the testes move from a position inside the abdominal cavity through a space called the inguinal canal. This process is completed by the time the foal is two weeks of age. The descent of the testes through the inguinal ring and into the scrotum is a result of contraction of the ligamentous gubernaculum testis, abdominal pressure and because the testicle is flaccid at this time^{footnote 1[1]}. When examining a neonate foal, one has to remember that the gubernaculum testis is large at birth and along with the epididymis are found ahead of the testicle^{footnote 1[1]}. Therefore, they can be mistaken for the testis^{footnote 2[2]}.

Three different forms of cryptorchidism are observed in horses: under the skin in the inguinal area (high flanker), in the inguinal canal (there are two inguinal rings: the superficial and the deep, the inguinal canal goes from the deep to the superficial inguinal ring) and in the abdomen. In one study of horses, the failure of the left and right testicles to descend into the scrotum occurs with nearly equal frequency. However, the left testicle is found in the abdomen in 75% of cryptorchid horses compared to 42% of right testicles. Bilateral cryptorchids, those with both undescended testicles and monorchid horses, those with only one developed testicle, are uncommon^{footnote 1[1]}. In bilateral cryptorchids, most of the time both testes are abdominal.

Causes of cryptorchidism

The retention of testes is a complex, incompletely understood process involving genetic, hormonal and mechanical factors. In dogs, it is believed to be an autosomal sex-linked recessive gene^{footnote 3[3]}.

Surgical techniques for the cryptorchid stallion

Until recently, the only surgical technique described for removal of retained testes was laparotomy under general anaesthesia. Recently, laparoscopy under general anaesthesia and laparoscopy while standing have been used to treat cryptorchidism in horses.

Laparotomy is the surgical opening of the abdomen under general anaesthesia by a number of surgical approaches including an inguinal approach with or without retrieval of the inguinal extension of the gubernaculum testis, a parainguinal approach (to the side of the inguinal ring), or, less commonly, a flank approach^{footnote 1[1]}. The inguinal and parainguinal approaches involve the incising of the skin, and blunt dissection down to the inguinal ring. The vaginal process, epididymis and/or scrotal ligament will be identified, the vaginal process opened, and the retained testis exteriorized and emasculated. If these structures are not identified, deeper dissection will be required. Special attention to the closure of the incision will be required since the intestine can eviscerate through the open vaginal process.

Laparoscopy is an endoscopic procedure where a small, fibre-optic, video camera and surgical instruments are introduced into the abdomen through a small incision. This permits the observation of the inside of the abdomen and allows for the performance of abdominal surgeries without a large incision into the abdominal cavity. The main advantages are the small incisions, minimal postoperative pain and the fact that the horse can return to exercise very quickly. Laparoscopy can be used to remove retained ABDOMINAL testes in horses. This procedure is currently being offered by a number of referral centres including the Ontario Veterinary College. Depending on the horse's temperament and on the surgeon's preference, the laparoscopic surgery will be performed in a standing position or laying down under general anaesthesia.

Standing laparoscopy is performed under local anaesthesia and tranquilization with the horse restrained in a set of stocks. It is relatively painless and minimally invasive. After sedation of the horse, local anaesthetics are injected to deaden nerve sensation to the flank area and three 1 cm incisions are made through the muscle layers of the flank into the abdominal cavity. These incisions are for the insertion of the laparoscopic camera and surgical instruments. During the procedure, carbon dioxide gas is used to inflate the abdominal cavity to allow for better visualization. Under laparoscopic guidance, the testis is ligated, emasculated and removed.

General anaesthesia laparoscopy involves the administration of general anaesthesia and placing the horse in dorsal recumbency (on its back). Once an adequate plain of anaesthesia is reached, small incisions are made in the abdominal wall. As in the standing laparoscopic procedure, the abdomen is inflated and the retained testis located and removed. The small incisions are closed and the horse recovered from anaesthesia. Both laparoscopic methods involve minimal invasion and pain but require more extensive equipment and specialized training to perform than open surgical procedures. Further information regarding laparoscopic surgical techniques can be obtained by contacting, Dr. Ludovic Boure at the Ontario Veterinary College 519-823-8800 or 519-824-4120, ext. 4037.

Complications

Complications can arise during normal castration as well as with the removal of retained testes. In routine castrations, horses will experience various degrees of postoperative swelling. Haemorrhage from the surgical sight will be minimal. In the case of excessive haemorrhage or inflammation, contact your veterinarian. On rare occasions, intestinal prolapse, infection of the spermatic cord (scirrhous cord), peritonitis (infection in the abdomen), hydrocele (fluid build-up in the vaginal tunic which surrounds the testes), damage to the penis and continued stallion-like behaviour may occur^{footnote 1[1]}.

Dealing with stallion-like behaviour

Sometimes it is necessary to determine whether a horse with no palpable testis, that displays a stallion-like behaviour, is a bilateral cryptorchid, a cryptorchid that has its descended testis removed, or a gelding with behaviour problems. These stallion-like horses can be a major source of frustration and cause aggravation to mares, which are in heat, and a danger to their handlers. In this situation, hormonal assays may be useful and include the analysis of basal plasma or serum testosterone or oestrone sulphate concentrations, testosterone concentrations following human chorionic gonadotrophin (hCG) stimulation, and faecal oestrone sulphate concentrations. Hormonal concentrations are lower in geldings than in cryptorchids. Unfortunately, none of the hormonal tests are 100% accurate and, often, surgical exploration of the abdomen is necessary. Until recently, laparotomy was the only way to explore the abdomen of these horses. Now laparoscopy can be used successfully for these purposes. Again, its main advantages are that the surgical incisions are small, the postoperative pain is minimal and the horse can go back to exercise soon after the surgery. Contact your local veterinarian for this and other health concerns you may have regarding your horse.