Excessive swelling of the scrotum in horses can result from trauma, disease and medical disorders. To diagnose the cause of scrotal swelling, a veterinarian may perform a physical exam, a palpitation of the scrotum and testes, an ultrasound, or a biopsy.
Swelling of the scrotum is normal after castration. Excessive swelling, however, may be an indication of complications, such as an infection at the operation site. Scrotal seroma, which are formations of clotted blood and fibrin strands, can also cause extreme swelling after castration.
Stallions are often kicked by the mare while breeding, which can cause trauma to the scrotum. A scrotal contusion or a testicular hematoma can also result from trauma.
Dourine is a severe venereal disease that affects horses and is transmitted typically through breeding. Swelling of the genitalia is a primary characteristic of dourine.
Infections and Parasites
Viral infections including equine viral arteritis, equine infectious anaemia, equine influenza, African horse sickness or other viral aetiologies can cause excessive scrotal swelling. Verminous orchitis can result from strongylus edentatus larvae.
Patent ruptured bladder syndrome may occur when urine is forced into the urachus and inguinal canals by a constant straining to urinate, which results in swelling of the scrotum. Ischemia, or a restriction of blood supply, can cause testicular torsion or thrombosis of the testicular artery, which also leads to extreme swelling of the testes and scrotum.