Could problems arising from castration be causing ongoing problems for geldings?
Fresh research suggests that neuromas are common at the site of castrations in horses, and scientists say more work is needed to discover if any of these cause pain or other issues.
Neuromas are unorganized bulbous or nodular masses of nerve fibers and other cells that can form on a severed nerve. They are benign and, in people, most cause no problems. However, in some cases they can be a source of considerable pain.
Researchers from the Swedish University of Agricultural Science raise the possibility that groin pain, unexplained hind limb lameness, back pain or behavioural problems in geldings could be attributable to painful neuromas that develop from the crushing and severing of the testicular nerves during castration.
However, the presence of neuromas in this region has, until now, never been reported.
Emma Angelina Bengtsdotter, Stina Ekman and Pia Haubro Andersen set out to microscopically examine the testicular nerves at the castration site in geldings for the presence of neuromas.
The trio, writing in the journal Acta Veterinaria Scandinavica, described how remnants of the right and left spermatic cord were collected from 20 geldings of different breeds and ages subject to routine post mortem examinations for various reasons unrelated to their castration.
The spermatic cord specimens were processed and stained so that the researchers could see whether neuromas were present.
Neuromas were found in 21 spermatic cords from 13 geldings. Eight of the geldings were found to have neuromas in both of their spermatic cord remnants.
“Further studies are required to establish if these neuromas in the castration site are painful and if certain castration methods promote their formation,” the trio wrote.
They say further work is also needed to determine the clinical consequence of these neuromas for the individual horse, and whether any particular castration techniques affect their formation.
Castration is the most commonly performed surgery in horses worldwide. It is performed either in a standing procedure, or the horse is rendered completely unconscious through short-acting intravenous anesthetics.
Most are performed as semi-closed castrations, where the testes are removed through scrotal skin. Bleeding is minimized by crushing the cord without the use of ligatures.
Scrotal wounds are left open for drainage.
The authors noted that while acute or short-term complications arising from castration, such as swelling, bleeding, and infection, are well-investigated, later complications are less studied.
“Horse owners may present geldings with rather vague signs occurring after the castration, such as changed behavior, gait and urination habits or decreased riding performance.
“While there are few studies on these problems, it is generally accepted that soreness related to the post-operative scar may be as a source of gait modification.”
Treatment can include surgical removal of scar tissue, including larger or smaller areas of fibrous tissues, at the castration site. However, no research has been performed on the outcome of the surgery or the possible process that gave rise to the problem.
Neuromas after castration have not, until now, been demonstrated in either animals or humans. However, neuromas caused by surgical trauma to peripheral nerves are described after tail docking in pigs, lambs and dogs, following nerve removal in horses, and beak trimming in poultry.
Neuromas are also described in the shoulder areas of sows with deep ulcerations.
“In human medicine, neuromas following amputation may cause chronic or neuropathic pain,” the researchers observed.
Discussing their findings, the study team noted that neuromas were found in 54% of the spermatic cords, belonging to 65% of the 20 geldings. These neuromas affected both cords in 40% of the horses.
“The neuromas found at the castration site had histological (microscopic) features compatible with traumatic neuromas described after tail docking in pigs.”
The length of the remnants of the spermatic cord did not appear to be correlated with the presence of neuromas, they said.
“Information about the horse’s age at castration or any post-surgical complications was not available, hence it was not possible to correlate the neuromas with age at castration or castration method.”
The authors noted that neuromas are more likely to form in traumatised and inflamed tissues. “Most equine traditional castration methods include severe damage of the nerves of the spermatic cord and inflammation or infection is one of the most common complications.
“In horses, most castration wounds are therefore left to secondary healing to eliminate inflammatory products from the crushed cords and tissues.”
Further, the groin is a highly mobile region, and in humans, it is known that inflammation and movement are factors in the development of painful neuromas.
“Consequently, if this also applies to horses, the current methods for castration may need revision.”
They continued: “Exactly why a neuroma becomes painful is not yet fully understood. It is not unlikely that at least some of the neuromas formed will be painful, given the anatomical location of the severed cords in a highly mobile area, and the high risk of formation of adherences due to infection.
“The present study was not, however, designed to answer whether the neuromas were painful.”
They noted that studies on human finger amputations report that 7.3% of the traumatic neuromas caused pain or altered sensation, and neuromas after inguinal hernia repair are often associated with chronic pain.
“Although the peripheral nerves differ from the testicular ones in sensory and motor composition, the mechanisms responsible for development of painful neuromas could be similar.
“Future research should aim at classifying the neuromas as painful or non-painful. This could be done both clinically and with biomarkers for pain.”
However, there are no validated methods for clinical investigation of horses with suspected painful castration neuromas.
“It is of great importance that such methods be developed. The clinical implications of possible chronic pain long after castration affect the welfare of the horse.”
Neuromas at the castration site in geldings
Emma Angelina Bengtsdotter, Stina Ekman and Pia Haubro Andersen
Acta Veterinaria Scandinavicavolume 61, Article number: 43 (2019) https://doi.org/10.1186/s13028-019-0479-8