Piglet surgical castration: why, how?

Surgical castration is an invasive and painful husbandry procedure commonly performed in piglets before the age of seven days.

This standard practice is performed in most European countries. Technically, it consists of a scrotal incision, the blunt dissection of testicular tissue from the surrounding fascia, and the hyper-extension of the spermatic cord until it spontaneously ruptures or is cut¹. The severing of the spermatic cord is thought to be the most painful part of the surgery for pigs².

Piglet surgical castration is primarily used to reduce the occurrence of “boar taint”, an unpleasant odour often found in meat from entire male pigs, caused by androstenone (male sex hormone), skatole and indole (both are produced respectively in the intestine from the breakdown of tryptophan) which are deposited in the fat tissue³. Pork meat displaying boar taint is not suitable for human consumption. Methods of boar taint detection vary, although the human nose detection remains the most frequently used practice.

Surgical castration is also used to prevent undesired sexual and aggressive behaviour in male pigs. Castrated males are less aggressive and easier to manage⁴. In addition to being a painful procedure, surgical castration often results in increased feed costs and increased fat content of the carcass⁵.

How to mitigate pain caused by piglet surgical castration

Current pain reduction strategies include the use of non-steroidal anti-inflammatory drugs (NSAIDs) prior to castration, as well as the use of local anaesthetics, and general anaesthesia. Licensed medicines to use for anaesthesia and analgesia for pig castration are limited. Furthermore, anaesthetic and analgesic protocols need to be cost-effective, practical, efficacious, safe (for the pig, the farmer and/or the vet and the environment) and produce minimum stress and pain.

Meloxicam, ketoprofen and flunixin are the most commonly used NSAIDs, although some studies suggest that their effectiveness in alleviating pain during surgical castration is questionable ¹⁰. The use of NSAIDs administered prior to the surgery seems to have an effect on post-operative pain, suggested by a reduction in pain-related behaviours post-surgically^10,11 (rump scratching, tail wagging). More specifically, the use of meloxicam prior to piglet castration seems to result in less pain-related behaviours afterwards, whether a local anaesthetic has been used or not^7,12.

Procaine is the only licensed drug to be used for pig castration¹⁰. Lidocaine does not have a maximum residue limit (MRL) and is therefore not allowed for use in food-producing animals in Europe; however, some countries like France allow its use for piglet surgical castration. It is worth noting that the injection of a local anaesthetic in the scrotum and testicles can cause additional pain and distress to piglets. When given a local anaesthetic, piglets exhibit a significant reduction in escape behaviour during castration^7,13. The use of topical anaesthetics (short or long acting) on the severed spermatic cords after castration and on scrotal incisions does not seem to result in a change of pain-related behaviours (bottom scooting, huddling)¹⁴. Using anaesthetics seem to be beneficial to piglets during surgical castration (demonstrable reduction in pain perception and stress response); however, without a combined use of an analgesic, piglets seem to experience pain after the procedure^10,15,16. General anaesthesia does not seem to result in any difference in pain-related behaviour after castration^{14, 17}, and is not commonly used for practical reasons, except in some countries such as Germany.

So, according to research, anaesthesia alone prevents pain during surgery, but not after, while analgesia alone mitigates pain after surgery, but not during it^5.

Fattening of male boars and immunocastration: alternatives to piglet surgical castration

There are several alternatives to surgical castration.

Raising entire male pigs is traditionally used in some countries such as Spain, Portugal, Ireland and the United Kingdom. From a welfare point of view, there is no castration, so no pain nor stress experienced by animals. There is no additional workload for the pig farmers either.

However, uncastrated pigs can display aggressive and sexual behaviours, detrimental to their welfare¹⁸. Feed efficiency and carcass quality are better than in surgically castrated pigs, however the meat quality is lower¹⁸ (presence of boar taint, reduced intramuscular fat content and reduced saturation of the fat). One way to address the presence of boar taint could be to slaughter entire males at a lower weight; however, this approach is not used currently for obvious economic reasons⁶. Some slaughterhouses have implemented “Human Nose Scores” based on recording boar taint after heating¹⁹. Also, research suggests the possibility of a genetic solution to decrease boar taint to abandon castration^3,18,19. As a matter of fact, as androstenone and skatole have moderate to high heritability, it is technically possible to genetically select against these compounds. Although this method seems promising, implementing such genetic selections strategies has a cost. Modifications of diet and environmental conditions could also decrease boar taint³.

Alternatives to surgical castration also include immunological castration, often referred as immunocastration, which aims is to delay the onset of puberty.  Immunocastration is not a hormonal treatment, meaning there are no hormonal residues issues, but stimulates the pig’s immune system to produce antibodies inhibiting testes function. The effect is temporary. It has been permitted in Europe since 2009. It requires two injections at least four weeks apart during the fattening phase of pigs, the second dose being given four to five weeks before slaughter²⁰.

Some countries, such as Belgium, display higher percentage of immunocastrated male pigs. Immunocastration prevents the occurrence of boar taint, removes the pain that would have been associated to a surgical castration, and prevents stress-related aggressive and sexual behaviours in male pigs^5,20. In this aspect, immunocastration clearly displays obvious welfare advantages compared to surgical castration. However, immunocastrated male pigs can sometimes display aggressive behaviour before the second injection, as immunocastration is only effective after the second vaccination¹⁸.

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