Cryptorchidism is failure of one or both testes to descend into the scrotum. Primary fault lies in the testis. We provide a unifying cross-species interpretation of testis descent and urge the use of precise terminology. After differentiation, a testis is relocated to the scrotum in three sequential phases: abdominal translocation, holding a testis near the internal inguinal ring as the abdominal cavity expands away, along with slight downward migration; transinguinal migration, moving a cauda epididymidis and testis through the abdominal wall; and inguinoscrotal migration, moving a s.c. cauda epididymidis and testis to the bottom of the scrotum. The gubernaculum enlarges under stimulation of insulin-like peptide 3, to anchor the testis in place during gradual abdominal translocation. Concurrently, testosterone masculinizes the genitofemoral nerve. Cylindrical downward growth of the peritoneal lining into the gubernaculum forms the vaginal process, cremaster muscle(s) develop within the gubernaculum, and the cranial suspensory ligament regresses (testosterone not obligatory for latter). Transinguinal migration of a testis is rapid, apparently mediated by intra-abdominal pressure. Testosterone is not obligatory for correct inguinoscrotal migration of testes. However, normally testosterone stimulates growth of the vaginal process, secretion of calcitonin gene-related peptide by the genitofemoral nerve to provide directional guidance to the gubernaculum, and then regression of the gubernaculum and constriction of the inguinal canal. Cryptorchidism is more common in companion animals, pigs, or humans (2-12%) than in cattle or sheep (< or =1%). Laboratory animals rarely are cryptorchid. In respect to non-scrotal locations, abdominal testes predominate in cats, dogs, and horses. Inguinal testes predominate in rabbits, are common in horses, and occasionally are found in cats and dogs. S.c. testes are found in cattle, cats and dogs, but are most common in humans.

/pdf/cryptorchidism-in-common-eutherian-mammals-2u8gp96oq9.pdf

Cryptorchidism in common eutherian mammals.

CHAPTER 5 – The Male Genital System

CHAPTER 1 – The Alimentary System

Plasma testosterone concentrations were measured by radioimmunoassay in a wild population of the male hibernating bat, Myotis lucifugus lucifugus, (Chiroptera;Vespertilionidae) throughout the entire annual reproductive cycle. Baseline levels (2.5 ± 0.3-11.7 ± 3.2 ng/ml) occur during the early phases of spermatogenesis (May to mid-July), during the breeding period (September to May) and throughout hibernation (late September to April). These levels are similar to those reported for most adult breeding mammals. During the latter part of spermatogenesis (mid-July to late August) and just prior to maximum hypertrophy of the sex accessory glands, plasma testosterone rises to very high levels with a peak (59.1 ± 9.2 ng/ml) occurring in mid-August. This peak is one of the highest known values for adult mammals. The data suggest that a testosterone surge is required to stimulate the accessory glands fully, but lower levels of androgen are able to support them (as well as epididymal sperm and libido) during the breeding and hibernation seasons. However, these “lower” levels apparently are not sufficient to maintain the accessories when the bats emerge from hibernation in the spring, because these glands involute soon thereafter.

/pdf/changes-in-plasma-testosterone-levels-during-the-annual-36ulm2820a.pdf

Changes in Plasma Testosterone Levels During the Annual Reproductive Cycle of the Hibernating Bat, Myotis lucifugus lucifugus with a Survey of Plasma Testosterone Levels in Adult Male Vertebrates

Complications associated with equine castration are the most common cause of malpractice claims against equine practitioners in North America. An understanding of the embryological development and surgical anatomy is essential to differentiate abnormal from normal structures and to minimise complications. Castration of the normal horse can be performed using sedation and regional anaesthesia while the horse is standing, or under general anaesthesia when it is recumbent. Castration of cryptorchid horses is best performed under general anaesthesia at a surgical facility. Techniques for castration include open, closed and half-closed techniques. Failure of left and right testicles to descend 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 cryptorchid and monorchid horses are uncommon. Surgical approaches described for the castration of cryptorchid horses include an inguinal approach with or without retrieval of the scrotal ligament, a parainguinal approach, or less commonly a suprapubic paramedian or flank approach. Laparoscopic castration of cryptorchid horses has recently been described but the technique has limited application in practice at this time. A definitive diagnosis of monorchidism can only be made after surgical exploration of the abdomen, removal of the normal testis and hormonal testing. Hormonal assays reported to be useful include analysis of basal plasma or serum testosterone or oestrone sulphate concentrations, testosterone concentrations following hCG stimulation, and faecal oestrone sulphate concentrations. Reported complications of castration include postoperative swelling, excessive haemorrhage, eventration, funiculitis, peritonitis, hydrocele, penile damage and continued stallion-like behaviour.

Equine castration: review of anatomy, approaches, techniques and complications in normal, cryptorchid and monorchid horses

UMMARY
Concentrations of testosterone in the peripheral plasma of normal, cryptorchid and castrated male horses have been measured by a rapid radioimmuno-assay. Basal concentrations in horses with one or two testicles range from 65 pg to 1600 pg/ml. Intravenous injection of 12000 i.u. of Human Chorionic Gonadotrophin (HCG) into horses possessing testicular tissue stimulated a rise in testosterone concentration which could be detected within 25–35 minutes of the injection.

Geldings consistently showed low testosterone concentrations in the plasma (15.3±4.9 pg/ml; 15 animals), and injection of HCG did not stimulate a significant rise in testosterone concentration.

Of 29 horses presented as rigs all those which were later found to have been already castrated had plasma testosterone concentrations indistinguishable from those found in geldings (nine animals) and failed to respond to HCG injection (five animals).

Evidence is presented that the epididymis and spermatic cord of the horse are not capable of producing significant quantities of testosterone.

The possibility is discussed of using paired blood samples, one taken prior to and the other taken after HCG injection, as a test of whether or not a horse has been castrated.

RESUME
Les concentrations de testosterone dans le plasma peripherique des chevaux males normaux, cryptorchides et castres ont ete mesures par des tests radio actifs.

La concentration de base chez les chevaux avec un ou deux testicules varie de 65 pg a 1600 pg/ml.

L'injection intraveineuse de 12000 U.I. de gonadotrophine chorionique humaine chez des chevaux possedant un tissu testiculaire entraina.

L'augmentation du taux de testosterone detectable entre 25 et 35 minutes apres l'injection.

Les chevaux hongres montrerent de basses concentrations plasmatiques de testosterone (15.3±4.9 pg—15 sujets) et l'administration de gonadotrophine ne provoqua aucune elevation significative du taux de testosterone chez eux.

Des 29 chevaux reputes cryptorchides tous ceux qui furent identifies plus tard comme ayant ete castres montrerent des concentrations plasmatiques de testosterone de meme ordre que les hongres, et ne presenterent aucune reponse a l'injection de gonadotrophine.

Il semble que ni le lepididyme ni le cordon spermatique du cheval ne soient capables de secreter des quantites significatives de testosterone.

On envisage la possibilite, en comparant deux echantillons de sang, l'un preleve avant, l'autre preleve apres l'injection de gonadotrophine chorionique, d'etablir si un cheval a ete ou n'a pas ete castre.

ZUSAMMENFASSUNG
Die Testosteronkonzentrationen im peripheren Plasma normaler, kryptorchider und kastrierter mannlicher Pferde wurden gemessen mit Hilfe eines schnellen radio-immuno-assay. Die Konzentrationen schwanken zwischen 65 bis 1600 pg/ml bei Pferden mit einem oder zwei Hoden. Die intravenose Injektion von 12'000 IU menschlichen Choriongonadotropins stimulierte einen Anstieg der Testosteronkonzentration bei Pferden mit Hodengewebe nach 25–35 Minuten.

Wallachen zeigten immer tiefe Testosteronkonzentration im Plasma (15,3±4.9 pg/ml, N=15) und die Injektion von Choriongonadotropin fuhrte nicht zu einem signifikanten Anstieg. Von 29 Pferden, die als Spitzhengste vorgestellt wurden, hatten alle diejenigen (9) tiefe Plasma-Testosteronkonzentration, die sich als schon kastriert herausstellten und sie sprachen auch nicht auf Choriongonadotropin an (5). Es wird gezeigt, dass Epididymis und Samenstrang beim Pferd keine signifikanten Testosteronmengen produzieren. Die Moglichkeit wird diskutiert, mit gepaarten Blutproben (vor und nach Choriongonadotropin-Injektion) abzuklaren, ob ein Pferd kastriert worden ist oder nicht.

Testosterone in Normal, Cryptorchid and Castrated Male Horses

The results of performing 1720 blood tests for equine cryptorchidism are described. Using the paired sample human chorionic gonadotrophin (hCG) stimulation test and measuring testosterone, 6.7 per cent of tests did not give a clear result. If only the testosterone concentration in the pre-hCG blood sample was used, this percentage rose to 14 per cent. The paired sample hCG stimulation test was 94.6 per cent accurate. A comparison was made between the paired hCG stimulation test and the measurement of conjugated oestrogen in a single sample. The latter did not give as many doubtfuls but gave false negatives in donkeys of all ages and in horses less than three years old. Measurement of conjugated oestrogen was found to be 96 per cent accurate when donkeys and young horses were excluded. It is, therefore, recommended as a simpler and more reliable test than the paired sample hCG test, but only in the older horse.

Comparison of the measurement of plasma testosterone and plasma oestrogens for the diagnosis of cryptorchidism in the horse

SUMMARY

The authors analyse data collected over 23 years from 500 cryptorchid horses. They show that left- and right-sided abdominal cases occur with approximately equal frequency in ponies. Approximately half the right-sided unilateral abdominal cases have the epididymal tail descended while only 20 per cent of the left-sided cases do. These findings are briefly discussed.



From their analysis of inguinal cryptorchidism the authors conclude that it is a relatively more complex phenomenon with incidence changing with age as well as breed. Right-sided retention predominates in young ponies, probably being an extreme expression of testicular hypoplasia, but in older ponies and in other types of horse, retention occurs equally on the left and right.



RESUME

Les auteurs analysent les donnees recueillies durant plus de 23 ans sur 500 chevaux cryptorchides. Ils montrent la frequence egale des cryptorchidies droite et gauche chez les poneys.



Pour environ 50%, les cryptorchidies dextres sont caracterisees par une migration de l'epididyme contre 20% pour les cryptorchidies senestres. On commente ces constatations.



Les auteurs concluent a propos du cryptorchidisme inguinal, qu'il s'agit d'un phenomene complexe dont la frequence varie avec l'âge et la race. Le cryptorchidisme inguinal dextre predomine alors chez les jeunes poneys et semble etre l'expression d'une hypoplasie testiculaire. Au contraire, chez les poneys adultes et dans les autres races, la migration incomplete est indifferemment droite ou gauche.



ZUSAMMENFASSUNG

Die Autoren analysieren die Daten, die sie wahrend 23 Jahren von 500 Kryptorchiden-Pferden gesammelt haben. Sie zeigen, dass Abdominal-Hoden bei Ponies links und rechts ungefahr mit gleicher Haufigkeit auftreten. Bei ungefahr der Halfte der rechtsseitigen, unilateralen, abdominalen Falle war der Epididymis-Schwanz abgestiegen, wahrend das nur bei 20% der linksseitigen Retentionen der Fall war. Diese Befunde werden kurz diskutiert.



Die Analyse des inguinalen Kryptorchidismus ergab, dass es sich dabei um einen verhaltnismassig komplexeren Vorgang handelt, wobei die Haufigkeit mit dem Alter und der Rasse variiert. Eine Rechtsretention pradominiert bei jungen Ponies—wobei es sich dabei um einen extremen Ausdruck einer Hoden-hypoplasie handeln konnte— wahrend bei alteren Ponies und bei anderen Pferderassen die Retention gleich haufig auf der linken wie auf der rechten Seite auftritt.

https://beva.onlinelibrary.wiley.com/doi/pdf/10.1111/j.2042-3306.1979.tb01321.x

An analysis of 500 cases of equine cryptorchidism.

SUMMARY

The author has investigated just over 100 horses which showed male behaviour, either sexual or aggressive or both, but had no visible or palpable testes. Blood samples were taken prior to and between 30 and 100 min after the intravenous injection of Human Chorionic Gonadotrophin. On the basis of the concentration of testosterone in the post-HCG sample, it was possible to designate all but 8 horses as either geldings (less than 40 pg/ml) or cryptorchids (more than 100 pg/ml). Surgical investigation confirmed the diagnosis in 23 geldings and 47 cryptorchids. Thirty horses were not operated on and all but one of these had post-HCG concentrations less than 40 pg/ml. The horses whose post-HCG concentration of testosterone lay between 40 and 100 pg/ml are discussed in detail.



RESUME

L'auteur a etudie le cas de quelques cent chevaux qui montraient un comportement de male, soit un comportement sexuel proprement dit soit une certaine aggressivite mais donc aucun ne presentait de testicule visible ou palpable. Des echantillons sanguins furent preleves sur ces animaux avant puis entre trente et cent minutes apres l'injection de Gonadotrophine Chorionique humaine.



En tenant compte de la concentration de testosterone presente dans les prelevements consecutifs a l'injection de G.C.H., il fut possible d'identifier tous les chevaux sauf huit comme etant soit des chevaux hongres (moins de 40 pg/ml) soit des chevaux cryptorchides (plus de 100 pg/ml).



On confirma ce diagnostic par investigation chirurgicale sur 23 hongres et sur 47 cryptorchides. 30 chevaux ne furent pas operes, qui avaient tous a l'exception d'un seul, une concentration de testosterone inferieure a 40 pg/ml, dans le second prelevement.



Le cas des chevaux ayant entre 40 pg et 100 pg ml est discute.



ZUSAMMENFASSUNG

Etwas uber 100 Pferde wurden untersucht, die mannliches Verhalten zeigten-sexuell oder aggressiv oder beides-, aber keine sicht- und tastbaren Hoden aufwiesen. Blutproben wurden vor und 30 bis 100 Minuten nach der intravenosen Injektion von humanem Choriongonadotropin genommen. Die Testosteron-Konzentration nach der HCG-Injektion erlaubte nur bei acht Pferden keine Unterscheidung von Wallachen ( 100 pg/ml). Die chirurgische Untersuchung der Pferde bestatigte die Diagnose bei 23 Wallachen und 47 Kryptorchiden. 30 Pferde wurden nicht operiert, von denen bis auf ein Tier alle Konzentrationen von <40 pg/ml nach der HCG-Injektion aufwiesen. Die Pferde mit Testosteronkonzentrationen zwischen 40 und 100 pg/ml nach HCG werden im Detail besprochen.

Experiences with a diagnostic test for equine cryptorchidism

The history of techniques for abdominal equine cryptorchidectomy is briefly reviewed. The technique of suprapubic paramedian laparotomy as used since 1955 at the University of Liverpool veterinary field station is described in detail and an account given of the authors' experience with the technique in nearly 200 cases. It is concluded that the approach to the abdominal cavity is easy, that the testis itself is generally readily located and removed and that controlled repair of the incision is possible. Serious post-operative complications are rare and the danger of post-operative prolapse of bowel eliminated.

J. E. Cox

Papers

Testosterone in Normal, Cryptorchid and Castrated Male Horses

Comparison of the measurement of plasma testosterone and plasma oestrogens for the diagnosis of cryptorchidism in the horse

An analysis of 500 cases of equine cryptorchidism.

Experiences with a diagnostic test for equine cryptorchidism

Suprapubic paramedian laparotomy for equine abdominal cryptorchidism.