Cryptorchidism is a congenital condition in male pigs where one or both testes fail to descend fully into the scrotum, affecting approximately 1% to 1.4% of male piglets in commercial swine production. The retained organ remains within the body cavity or inguinal canal. This developmental failure has significant economic consequences for producers, primarily related to reduced meat quality and the inability to use affected animals for breeding. Because of its heritable nature, managing cryptorchidism requires both immediate intervention and long-term genetic selection.
The Biological Basis and Causes
Testicular descent is a two-phase developmental process in the pig. The first phase, the transabdominal phase, involves movement of the testes from near the kidney down to the inguinal region, controlled largely by the hormone Insulin-like Factor 3 (INSL3). The second phase, the inguinoscrotal phase, involves passage through the inguinal canal into the scrotum, guided by the gubernaculum and dependent on androgens like testosterone. Failure at either step results in cryptorchidism, with the retained testicle most commonly found in the abdominal cavity or the inguinal canal.
The condition is considered a complex multigenic trait, meaning multiple genes contribute to an individual’s susceptibility. Heritability estimates generally range between 0.06 and 0.33, indicating a moderate to significant genetic component. This genetic predisposition can be influenced by hormonal imbalances during fetal development, as studies show that exposure to antiandrogens can induce cryptorchidism in pigs.
Cryptorchidism is categorized as either unilateral (one testicle retained) or bilateral (both testicles fail to descend). Unilateral cases are more common in swine and other domestic animals, and the right testicle is often the one retained. The underlying issue is a developmental failure linked to genetics and hormonal signaling pathways.
Identification and Diagnosis
Detecting cryptorchidism in piglets is a straightforward physical examination typically performed during the routine processing of newborns, such as iron injections or tail docking. Since the testicles are normally descended at birth in swine, a hands-on check allows for early identification.
The primary method of diagnosis is visual inspection and palpation of the scrotal sac. A piglet with cryptorchidism will show either an absence of testicles in the scrotum or an obvious asymmetry, where one side appears normal and the other side is flat or undersized. Palpation involves gently feeling the inguinal region and abdomen to locate the missing testicle.
In most cases, the retained testicle can be palpated either high in the inguinal canal or just inside the abdomen near the inguinal ring. Early detection is important for making management decisions before the animal is moved to the finishing floor.
Production and Health Implications
The consequences of cryptorchidism affect both the animal’s reproductive capability and the quality of the pork product. A bilateral cryptorchid (both testes retained) is sterile because the higher internal body temperature prevents sperm production, though it can still produce hormones. A unilateral cryptorchid, which has one descended testicle, is fertile and capable of producing viable semen.
The most substantial economic problem is “boar taint,” an offensive odor and flavor in the meat that makes it unacceptable to consumers. Retained testes, even if only one is present, continue to produce high levels of the pheromone androstenone. Unlike normal castration, a retained testicle remains in the body and releases androstenone into the bloodstream, where it accumulates in the pig’s fat tissue.
This undesirable meat quality results in discounted prices or carcass condemnation at the packing plant, leading to financial loss for the producer. Additionally, the retained testicle is at a higher risk of developing testicular neoplasia later in the animal’s life due to the elevated temperature environment.
Management Strategies
Once cryptorchidism is confirmed, the management strategy focuses on preventing boar taint and removing the genetic defect from the breeding population. To eliminate the risk of boar taint, surgical removal of the retained testicle is necessary before the pig reaches market weight. This procedure, known as cryptorchidectomy, is more complex than a standard castration because the surgeon must locate the testicle, which is often deep within the inguinal canal or abdominal cavity.
The most common surgical approach involves an incision over the inguinal ring to locate and remove the undescended gonad, sometimes requiring entry into the abdomen. Because of the complexity and risk of infection associated with abdominal surgery, this procedure should be performed by an experienced veterinarian. Following successful surgery, the pig can be finished for market like a castrated male, or barrow, without the risk of boar taint.
The long-term strategy for managing cryptorchidism is rigorous genetic control within the herd. Affected boars, even those with only unilateral cryptorchidism, should never be used for breeding due to the high heritability of the condition. Sows that consistently produce cryptorchid piglets should also be culled from the breeding herd to reduce the incidence in future generations. Selective breeding against this polygenic trait is the most effective way to lower the prevalence and the associated economic losses.