Cryptorchidism: What the Research Says
Evidence from 20 peer-reviewed studies
What Professionals Should Know
- •Stallion-like behavior in geldings is rarely due to missed testicular tissue—investigate other behavioral or management factors before assuming cryptorchidism
- •Hormone testing (testosterone and AMH) can help rule out cryptorchidism but results may not always align; interpret patterns rather than single values
- •Behavioral issues in geldings require a broader diagnostic approach beyond endocrine evaluation, including consideration of learned behavior, environmental triggers, and neurological factors
- •Cryptorchid stallions with ultrasonographic evidence of unusual parallel hyperechogenic lines within the retained testis should be evaluated for possible parasitic migration, particularly S. vulgaris
- •Laparoscopic removal remains a viable diagnostic and therapeutic approach for retained testes with suspected parasitic involvement
- •Clinicians should be aware that aberrant S. vulgaris localization in retained testes, while uncommon, is possible and may present with non-homogeneous testicular ultrasound findings
- •A cost-effective, custom-built single-access multiport device can enable standing laparoscopic cryptorchidectomy in horses, reducing need for general anesthesia
- •The device successfully diagnosed retained testicle complications (adhesions, ectopic locations) when surgical removal wasn't immediately feasible
- •This prototype technique may expand minimally invasive surgical options for standing horses, though further refinement and larger trials are needed before routine clinical adoption
- •Cryptorchidism in horses results in temperature-sensitive gene expression changes that impair spermatogenesis; consider surgical intervention early to preserve testicular function and fertility
- •Genetic screening for the identified missense mutations may help identify predisposed breeding stock and inform breeding decisions
- •Understanding the molecular basis of cryptorchidism-induced infertility can guide treatment timing and help counsel owners on prognosis for affected stallions
- •Cryptorchidism in stallions involves distinct miRNA expression changes that may provide new diagnostic markers for identifying subfertility in breeding soundness examinations
- •The identified miRNA signatures could eventually support development of molecular tests to assess testicular function and fertility potential before clinical signs of testicular dysfunction appear
- •Understanding miRNA dysregulation in undescended testes may inform future therapeutic approaches to preserve fertility in horses with unilateral cryptorchidism
- •Chitosan-based hemostatic agents offer a viable alternative for controlling severe hemorrhage in equine surgical cases when conventional methods fail
- •Be aware of external pudendal artery location in the medial commissure of the inguinal canal during cryptorchidectomy to avoid laceration
- •Consider chitosan products as a backup tool in your surgical kit for managing unexpected major bleeding complications
- •Laparoscopic cryptorchidectomy with vessel-sealing devices offers a safe, effective alternative to traditional open castration for retained testes in standing or recumbent positions, with mean surgery time under 35 minutes
- •The technique successfully managed various cryptorchid presentations including bilateral cases and previously failed removals with no recorded complications
- •Dorsal recumbency positioning allows surgeon control of inguinal testes and reduces risk of peritoneal contamination compared to traditional approaches
- •Epididymal-testicular fusion anatomical variations exist in stallions and may have clinical relevance; awareness of these patterns is important when evaluating breeding stallions or performing castrations
- •Elongated proper ligaments of the testis are associated with cryptorchidism in 95% of cases but can also occur in normally descended scrotal testes (34%), suggesting this anatomical variant warrants monitoring
- •Dorsal insertion of elongated proper ligaments predisposes to epididymal dislocation; stallions with this anatomy may be at risk for epididymal dysfunction and reproductive complications
- •CSL regression failure is an uncommon cryptorchidism cause but should be considered in cases with retained abdominal testes located near the kidney
- •Standing laparoscopic approach is a viable option for cryptorchidectomy in select cases, reducing recovery time compared to open celiotomy
- •Surgical exploration of the dorsocaudal abdomen is necessary to identify and remove testes attached by persistent CSL; vascular pedicle and ductus deferens ligation ensures safe removal
- •Cryptorchid testes in stallions demonstrate molecular characteristics of immaturity rather than degeneration, helping explain poor fertility outcomes
- •Early castration of cryptorchid stallions prevents prolonged testicular dysfunction; the undescended testis cannot recover normal function
- •Knowledge of these molecular changes supports clinical decision-making regarding breeding soundness examinations and castration timing in horses with cryptorchidism
- •Standing laparoscopic surgery is a viable and minimally invasive alternative for removing large cryptorchid testicular tumours when standard inguinal approaches are impractical
- •Pre-operative ultrasound-guided fluid aspiration can significantly reduce tumour mass and improve surgical access and handling during laparoscopic retrieval
- •Specimen pouches should be used during laparoscopic removal of testicular neoplasms to maintain pneumoperitoneum and prevent potential tumour cell dissemination
- •This foundational research establishes normal connexin 43 patterns in stallion reproductive tissues, which may help identify abnormal tissue changes in diseased or cryptorchid animals
- •Understanding gap junction protein expression could inform future diagnostic approaches to reproductive tissue pathology in breeding stallions
- •Results provide a reference standard for comparing connexin 43 expression in pathological conditions affecting stallion fertility
- •Recognize that laparoscopic castration of cryptorchids may fail in a small percentage of cases due to the testis's complex blood supply—have contingency surgical plans
- •Understanding the anatomical vascular complexity of the equine testis is essential for performing safe laparoscopic castration and managing complications
- •Consider anatomical factors when counseling clients about cryptorchid castration outcomes and potential need for repeat procedures or alternative approaches
- •This preliminary work identifies the cellular locations where androgens act in equine reproductive tissues, providing foundational knowledge for understanding how retained testes (cryptorchidism) may alter normal tissue regulation
- •The stronger AR expression in cryptorchid tissue suggests potential pathological changes in hormone-responsive cells that could have clinical implications for retained testicle management
- •Understanding androgen receptor distribution may inform future research into reproductive dysfunction in stallions and cryptorchid horses
- •Standing laparoscopic cryptorchidectomy using electrosurgical hemostasis is a safe, effective alternative to traditional castration methods for retained testes in standing horses.
- •Bipolar electrosurgical forceps reliably coagulate mesorchial vessels without causing complications, making this technique practical for field or clinic use.
- •This approach allows horses to remain standing throughout the procedure, reducing anesthesia risks and recovery time compared to recumbent surgery.
- •This laparoscopic cryptorchidectomy technique is suitable for younger horses (<3 years) and offers an alternative to traditional methods with reasonable operative times after initial experience
- •Expect a learning curve—initial cases take longer but improve significantly after 4 procedures; bleeding control is generally good but be prepared for occasional hemoabdomen requiring ultrasound monitoring
- •The resorbable loop device requires specific knowledge of application technique but does not demand extensive laparoscopic expertise, making it accessible to many equine surgeons
- •Consider breed predisposition when screening Quarter Horses and Appaloosas; cryptorchidism is 4–5 times more common in these Western riding breeds than others
- •Standing laparoscopy is the preferred technique for abdominal cryptorchidectomy with fewer significant complications; expect emphysema and minor spermatic cord bleeding but not serious morbidity
- •Transabdominal ultrasound is the most reliable diagnostic method (61.2% success rate); combine with per rectum palpation if ultrasound findings are inconclusive
- •The inguinal approach for cryptorchidectomy in pigs is a highly effective minimally-invasive technique already proven successful in horses, dogs, and cats
- •This on-farm surgical method has low complication rates and rapid completion times, making it practical for field use in swine production
- •Surgeons should be prepared to manage gubernaculum rupture in approximately 8% of cases using simple finger and forceps retrieval through the inguinal ring
- •Transabdominal ultrasonography is a safe, non-hazardous alternative to transrectal ultrasound for localizing cryptorchid testes, particularly useful for fractious, young, or small horses
- •The technique provides immediate, precise anatomical localization to guide surgical approach selection, improving surgical planning and efficiency
- •Ensure adequate clipping or grooming of the surgical site before imaging, as heavy hair coats can compromise image quality and lead to missed lesions
- •Minimally invasive laparoscopic approaches can be offered as alternatives to traditional open surgery for various abdominal conditions, reducing recovery time and complications.
- •Post-operative management significantly impacts outcomes; consider using prokinetic agents for ileus prevention, polymyxin B for endotoxaemia, and adhesion-prevention strategies such as peritoneal lavage with indwelling drains.
- •Modern surgical materials and techniques including stapling devices and selective COX-2 inhibitors can improve safety and reduce complications in abdominal surgery cases.
Key Research Findings
80.6% of geldings with stallion-like behavior had testosterone below cryptorchid reference range (<60 pg/mL), indicating testicular tissue is not present in most behaviorally problematic geldings
77.8% of behaviorally affected geldings had AMH below cryptorchid threshold (≤0.15 ng/mL), further suggesting absent testicular tissue
4.3% of samples showed elevated AMH suggesting cryptorchidism but normal testosterone, indicating hormonal discordance in some cases
Age affected both AMH and testosterone concentrations in presumptive cryptorchid stallions, while season had no effect
A retained abdominal testis in a 3-year-old Quarter horse stallion contained two live adult Strongylus vulgaris nematodes within blood-filled tracks in the testicular parenchyma
Ultrasonography revealed two parallel hyperechogenic lines resembling a cylindrical cavitary foreign body within a non-homogeneous testicular area
Histologically, the parasite tracks were characterized by lymphoplasmacytic infiltrates with abundant hemorrhage invading surrounding testicular structures
This case represents one of the few documented reports of S. vulgaris aberrant migration into a cryptorchid equine testis, confirming the rarity of this localization
A custom single-port multiport device enabled laparoscopic exploration of the abdominal cavity in standing horses via the paralumbar fossa
The device successfully facilitated cryptorchidectomy in 2 of 4 cryptorchid horses using two Babcock forceps for manipulation
In the other 2 cryptorchid cases, the device allowed diagnosis of adhesions and ectopic testicle locations in the inguinal region
Wide abdominal cavity exploration was achieved in all 5 bovine fetal cadaver trials with effective intra-abdominal structure manipulation
11 genes were downregulated in undescended testes compared to descended testes, likely due to higher abdominal temperature
These 11 downregulated genes have been previously associated with male reproduction and may explain reduced fertility in cryptorchid horses
Two homozygous missense mutations were identified in cryptorchid horses that were absent in normal horses, representing potential pathogenic variants
Evidence Base
Limited association between stallion-like behavior and hormonal indicators of testicular remnants in geldings.
Omyla K, Conley A, Varner D et al. (2024) — Journal of equine veterinary science
What is the "train track" in the retained equine testis?
Giorgio S Di, Monti S, Palmieri V et al. (2025) — Journal of equine veterinary science
A Single-Port, Multiple-Access, Custom-Made Device Used in Laparoscopically Assisted Cryptorchidectomy in Standing Horses-A Preliminary Study.
Silva Rafaela das Mercês, Araújo Luiz Henrique Vilela, Cardoso Thiago da Silva et al. (2024) — Animals : an open access journal from MDPI
Transcriptomic Analysis of Testicular Gene Expression in Normal and Cryptorchid Horses.
Han Haoyuan, Dong Hong, Chen Qiuming et al. (2020) — Animals : an open access journal from MDPI
Comparative Transcriptomics Analysis of Testicular miRNA from Cryptorchid and Normal Horses.
Han Haoyuan, Chen Qiuming, Gao Yuan et al. (2020) — Animals : an open access journal from MDPI
Chitosan-based agent use for hemostasis after cryptorchidectomy in a horse.
Tucker Michelle L, Wilson David G, Barber Spencer M (2020) — Veterinary surgery : VS
Laparoscopic cryptorchidectomy with a vessel-sealing device in dorsal recumbent horses: 43 cases.
Bracamonte José L, Thomas Keri L (2017) — Veterinary surgery : VS
Anatomical variations in epididymal-testicular fusion in stallions and their possible clinical significance.
Pozor M, Freeman D, Troedsson M et al. (2016) — Equine veterinary journal
Surgical treatment of 4 horses for cryptorchidism caused by failure of regression of the cranial suspensory ligament of the testis.
Ortved Kyla F, Stewart Allison Worster, Fubini Susan L et al. (2014) — Veterinary surgery : VS
Expression of anti-Müllerian hormone, CDKN1B, connexin 43, androgen receptor and steroidogenic enzymes in the equine cryptorchid testis.
Almeida J, Conley A J, Ball B A (2013) — Equine veterinary journal
Laparoscopic removal of a large abdominal testicular teratoma in a standing horse.
Cribb Nicola C, Bouré Ludovic P (2010) — Veterinary surgery : VS
Expression of connexin 43 protein in testes, epididymides and prostates of stallions.
Hejmej A, Kotula-Balak M, Sadowska J et al. (2007) — Equine veterinary journal
The complex blood supply to the equine testis as a cause of failure in laparoscopic castration.
Voermans M, Rijkenhuizen A B M, van der Velden M A (2006) — Equine veterinary journal
The presence of androgen receptors in the epididymis and prostate of the stallion and cryptorchid horse--a preliminary study.
Hejmej Anna, Wiszniewska Barbara, Kosiniak-Kamysz Kazimierz et al. (2006) — Veterinary journal (London, England : 1997)
Laparoscopic cryptorchidectomy using electrosurgical instrumentation in standing horses.
Hanrath Monique, Rodgerson Dwayne H (2002) — Veterinary surgery : VS
Laparoscopic cryptorchidectomy using a resorbable self-locking loop device in dorsally recumbent horses.
Bonomelli Natacha, Höglund Odd Viking, Bonilla Alvaro G (2024) — Veterinary surgery : VS
A Retrospective Study of Cryptorchidectomy in Horses: Diagnosis, Treatment, Outcome and Complications in 70 Cases.
Straticò Paola, Varasano Vincenzo, Guerri Giulia et al. (2020) — Animals : an open access journal from MDPI
Pig surgery: cryptorchidectomy using an inguinal approach.
Scollo A, Martelli P, Borri E et al. (2016) — The Veterinary record
Use of transabdominal ultrasonography to determine the location of cryptorchid testes in the horse.
Schambourg M A, Farley J A, Marcoux M et al. (2006) — Equine veterinary journal
Recent advances in equine abdominal surgery.
Smith C L, Dowling B A, Dart A J (2005) — Veterinary journal (London, England : 1997)