Welfare Implications of Swine Castration

Literature Review

May 25, 2013

This peer-reviewed summary has been prepared by the American Veterinary Medical Association Animal Welfare Division. While principally a review of the scientific literature, it may also include information gleaned from proprietary data, legislative and regulatory review, market conditions, and scholarly ethical assessments. It is provided as information and its contents should not be construed as official AVMA policy. Mention of trade names, products, commercial practices or organizations does not imply endorsement by the American Veterinary Medical Association.

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The issue

Castration of male piglets is a common practice in many countries and the vast majority of male piglets in the United States are castrated. Castration is performed to avoid boar taint in the meat of sexually mature male pigs and to reduce aggression toward other pigs and caretakers. Boar taint is an accumulation of compounds, such as skatole and androstenone, in the meat of intact males that cause an unpleasant smell and taste that is released when pork is heated. About 75% of consumers find meat from boars objectionable in comparison with meat from castrated males (barrows). The prevalence and intensity of consumer preference varies on the basis of human genotype. Barrows can be raised beyond puberty without developing strong boar taint, however they have poorer feed conversion and more fat deposits than boars. In addition to a reduction in the risk of boar taint, barrows exhibit less sexual and aggressive behavior,3  which makes them easier to handle and less likely to fight and injure each other each other in group pens.
Currently there are two methods of castrating male piglets: surgical castration and immunocastration.

Surgical Castration—Surgical castration of piglets is carried out prior to weaning, most commonly within the first three days of life. Piglets may be restrained for castration in a variety of ways including suspension by the hind legs using a castration stand or another stockperson, placement in a V-trough, or being held with a hand or between an individual’s legs.4  After the piglet is secure, either two vertical cuts or one horizontal cut is made to the skin of the scrotum, and the testes are removed by cutting the spermatic cord with a scalpel or pulling until the cord tears.4 Castration is typically performed without anesthesia or analgesia.3,4,5,6  

Immunocastration—Immunocastration involves injection of a protein compound that works like an immunization to induce antibody production against gonadotropin releasing hormone (GnRH). The process requires two injections: the first 8 to 11 weeks prior to slaughter and the second 4 weeks prior to slaughter. Immunocastration results in decreased production of gonadal steroids (testosterone and androstenone) with an associated increase in metabolism of skatole.7  Accordingly, there is a reduction in boar taint. Immunocastration is a temporary form of castration. Currently there is one product on the market that can be used for immunocastration of male pigs; Improvest® is an FDA-approved veterinary prescription product in the United States. This product is also labeled as Improvac™, a global brand that is approved for use in more than 60 other countries. Immunocastration is effective at reducing sexual and aggressive behaviors in male pigs (e.g. mounting,8,9,10  knocking,9 and fighting9) during the period the pig is immunocastrated.

Additionally, immunocastrated males have higher growth11 and lower feed conversion10,11 rates than physically castrated males. Recently, a pilot study with a limited sample size suggested that immunocastrated males were less vocal during handling and loading for processing, and that fewer dead and non-ambulatory pigs were observed with immunocastration as compared to surgical castration.12 While reported, the latter finding was not statistically significant.


aImprovest is a registered trademark of Zoetis

Human attitudes

A survey of Flemish pig producers showed that farmers perceive surgical castration without anesthesia as the best strategy with regard to profitability, performance and reduction of boar taint; however, they expected the lowest consumer acceptance for this strategy.  The farmers ranked surgical castration with anesthesia as the most labor intensive and production of intact males as the least profitable and least effective at reducing boar taint.13
Consumers are not generally aware that pigs are castrated nor are they aware of boar taint.14,15  When informed, consumers view surgical castration without anesthesia as a serious animal welfare concern.14,15,16,17,18 A survey of Swedish consumers and Belgian students showed that immunocastration was viewed positively and preferred over surgical castration or no castration,16,17 while a similar survey of consumers in Norway showed them to be skeptical about the product.14


Surgical castration involves cutting and manipulating innervated tissues18,19  and if anesthesia is not provided it will be painful6,14,20 as reflected by elevated blood cortisol concentrations,14,21,22  high-pitched squealing,22,23,24 and pain-indicative behaviors, such as trembling and lying alone.25,26  Some behavioral indicators of pain may persist for up to five days.23 The use of a local or general anesthetic is mandatory in Norway, Switzerland and the Netherlands for pigs entering their domestic markets.4 To avoid the pain associated with surgical castration other countries, such as the United Kingdom and Ireland, have elected to market nearly all of their male pigs intact.4


Potential complications associated with surgical castration include hemorrhage, excessive swelling or edema, infection, poor wound healing, and failure to remove both testicles. It has been suggested that surgically castrated barrows suffer from suppressed immunity,27  and exhibit higher incidences of inflammation, pneumonia and other diseases.28  With immunocastration, complications are similar to those of any other injection of pigs approaching market weight.  These would include injection site lesions, needles snapping off in the pigs, handling stress to the pigs, and specifically for immunocastration, risk of self-injection to the stockperson.

Anesthesia and analgesia

General anesthesia—Anesthesia can be induced by use of inhalation agents. Carbon dioxide29 is effective but causes distress in piglets.30,31   Halothane27 and isoflurane32,33,34 are also effective and do not seem to cause distress. Nitrous oxide is effective in inducing anesthesia, but is not effective at preventing pain from castration.35 On-farm use of anesthesia is rare due to a range of economic, logistical and safety issues, both for the pig and the herdsperson. Use of injectable general anesthetics is not recommended because of high mortality rates,36 and long recovery periods and risk of crushing by the sow.37
Local anesthesia—The most commonly used local anesthetic is lidocaine,38,39  which has been shown to reduce responses (as measured by EEG) that are indicative40 of nociception and behavioral responses that are indicative of pain.41,42  Piglets castrated with lidocaine also produce lower intensity vocalizations3,22 and struggle less during the procedure.3  Another study found that piglets that received lidocaine nursed significantly sooner after castration and those same piglets huddled less than a control group in which saline was used.43  Local anesthesia during castration is mandatory in Norway38 although its overall efficacy in improving welfare is questioned by some farmers because it requires extra handling, an injection and castration is performed at a later age.44  Procedures such as removal of piglets from the sow and injections cause marked discomfort and might be further refined.45
Analgesia—Lidocaine in combination with meloxicam may provide the most comprehensive pain relief for surgically castrated piglets.40,43 Piglets that received both lidocaine and meloxicam at castration nursed significantly sooner after the procedure and were more social at 24 hours after the procedure.43 In one study piglets given meloxicam displayed fewer pain-related behaviors including: huddling, spasms, rump scratching, stiffness and prostration.3 Flunixin has also been used;  however, its effectiveness is unknown and may be poor.28 Aspirin and butorphanol appear to be ineffective.47 
Availability and use of pharmaceuticals— Although combined use of an anesthetic and analgesic appears to be the most effective method for controlling pain associated with surgical castration, regulatory requirements and cost remain obstacles to practical application. Use of pharmaceuticals can burden producers with direct and indirect costs; the latter are associated with time delays and a potential need for additional veterinary assistance. Extra-label use of anesthetics and analgesics, while an option, is not ideal. Knowledge of effectiveness is not as great as it is for drugs approved for particular species and purposes. Extra-label use can also discourage research and development necessary to approve drugs for specific purposes.


Surgical castration has not been performed for many years in some countries including the United Kingdom, Ireland, New Zealand, and Australia. In most cases the approach to minimizing boar taint was slaughter of pigs before puberty. One study has shown that entire males spend more time performing social behaviors, including aggressive behaviors and mounting than surgical or immunocastrated males at 21 weeks of age.48  However, another recent study on raising entire males in stable groups showed that while there is a higher level of agonistic behavior after transfer to the finishing pen, there are not strong negative behavioral consequences overall.49  In Australia and New Zealand immunocastration has been in use since 1998.12
Selection—Boar taint has a genetic component and may be reduced through breeding.50
Sperm selection—Although current technology is not efficient enough for commercial use, it might be further developed to allow the production of only female piglets.51


Surgical castration is a painful procedure and animal welfare would be improved if it was performed with pain management, or replaced by a less invasive procedure. Immunocastration is a viable alternative to surgical castration that requires veterinary oversight within the United States.

1. Banon S, Andreu C, Laencina J et al. Fresh and eating pork from entire and castrate heavy males. Food Qual Pref 2004;3:293-300.
2. Weiler U, Font I, Furnols M, Fischer K et al.  Influence of differences in sensitivity of Spanish and German consumers to perceive androstenone on the acceptance of boar meat differing in skatole and androstenone concentrations. Meat Sci 2000;54:297-304.
3. Hansson M, Lundelheim N, Nyman G et al. Effect of local anaesthesia and/or analgesia on pain responses induced by piglet castration. Acta Veterinaria Scandinavica. 2011;53:34-43.
4. Rault JL, Lay DC, Marchant-Forde JN. Castration induced pain in pigs and other livestock. Anim Behav Sci 2011;135(3):214-225.
5. Hewson CJ, Dohoo IR, Lemke KA, et al. Canadian veterinarians’ use of analgesics in cattle, pigs, and horses. Canad Vet J 2007;48:155-164.
6. Lumb S. Towards a more ‘humane’ castration for piglets. Pig Progress 2007;23:24-26.
7. Quiniou N, Monziols M, Colin F et al. Effect of feed restriction on the performance and behaviour of pigs immunologically castrated with Improvac®. Animal. 2012;6(9):1420-1426.
8. Rydhmer L, Lundstrom K, Andersson K. Immunocastration reduces aggressive and sexual behaviour in male pigs. Animal. 2010;4(6):965-972.
9 Brewster V and Nevel A. Immunocastration with ImprovacTM reduces aggressive and sexual behaviours in male pigs. Appl Anim Behav Sci. 2013;145(1):32-36.
10. Fabrega E, Velarde A, Cros J, et al. Effect of vaccination against gonadotrophin-releasing hormone, using Improvac®, on growth performance, body composition, behaviour and acute phase proteins. Livestock Sci. 2010;132(1-3):53-59.
11. Batorek N, Cande-Potokar M, Bonneau M et al. Meta-analysis of the effect of immunocastration on production performance, reproductive organs and boar taint compounds in pigs. Animal. 2012;6(8):1330-1338.
12. Guay K, Davis B, Sapkota A et al. Behavior and handling of physically- and immunologically-castrated market pigs at home and going to market. AASV Proceedings. 2013;44:397(Abstr.).
13. Tuyttens FAM, Vanhonacker F, Verhille B, et al. Pig producer attitude towards surgical castration of piglets without anaesthesia versus alternative strategies. Res Vet Sci.2012;92(3):524-530.
14. Fredriksen B, Johnsen AMS and Skuterud E. Consumer attitudes towards castration of piglets and alternatives to surgical castration. Res Vet Sci. 2011;90(2):352-357.
15. Huber-Eicher B and Spring P. Attitudes of Swiss consumers towards meat from entire or immunocastrated boars: A representative survey. Res Vet Sci. 2008;85:625-627.
16. Tuyttens FAM, Vanhonacker F, Langendries K, et al. Effect of information provisioning on attitude toward surgical castration of male piglets and alternative strategies for avoiding boar taint. Res Vet Sci. 2011;91:327-332.
17 Vanhonacker F and Verbeke W. Consumer response to the possible use of a vaccine method to control boar taint v/ physical piglet castration with anaesthesia: a quantitative study in four European countries. Animal. 2011;5(7):1107-1118.
18 EFSA Welfare aspects of the castration of piglets, scientific report of the scientific panel for animals health and welfare, European Food Safety Authority. Available at: http://www.efsa.europa.eu/en/science/ahaw/ahaw_opinions/512.html Accessed August 7, 2007.
19. Prunier A, Bonneau M, von Borelli EH et al. A review of the welfare consequences of surgical castration in piglets and the evaluation of non-surgical methods. Anim Welf 2006;15:277-289.
20. National Pork Board. Swine welfare fact sheet: neonatal management practices. Available at: http://porkcdn.s3.amazonaws.com/sites/all/files/documents/Factsheets/Well-Being/SWINE%20WELFAREFACTSHT-neona.pdf​ Accessed November 19. 2015.
21. Carroll JA, Berg EL, Strauch TA, et al. Hormonal profiles, behavioral responses, and short-term growth performance after castration of pigs at three, six, or twelve days of age. J Anim Sci 2006;84:1271-1278.
22 Kluivers-Poodt M, Houx BB, Robben SRM, et al. Effects of a local anaesthetic and NSAID in castration of piglets on the acute pain responses, growth and mortality. Animal. 2012;6(9):1469-1475.
23 Puppe B, Schon PC, Tuchscherer A, et al. Castration-induced vocalization in domestic piglets, sus scrofa: comples and specific alteration of the vocal quality. Appl Anim Behav Sci 2005;95:67-78.
24. Taylor and Weary. Vocal responses of piglets to castration: identifying procedural sources of pain. Appl Anim Behav Sci 2000 Nov 1;70(1):17-26.
25. Hay M, Vulin A, Genin S, et al. Assessment of pain induced by castration in piglets: behavioral and physiological responses over the subsequent 5 days. Appl Anim Behav Sci 2003;3:201-218.
26. Moya AL, Boyle L, Lynch PB, et al. Effect of surgical castration on the welfare of 5-day-old piglets. Proceeding of the 38th International Congress of the ISAE 2004.
27. Weary DM, Fraser D. Partial tooth-clipping of suckling pigs: effects on neonatal competition and facial injuries. Appl Anim Behav Sci 1999;65:21-27.
28. Giersing M, Ladewig J, Forkman B. Animal welfare aspects of preventing boar taint. Acta Vet Scand 2006;48:S3
29. Svendsen O. Castration of piglets under carbon dioxide (CO2) anaesthesia. J Vet Pharmacol Therap 2006;29:47-59.
30. Prunier A, Bonneau M. Y a-t-il des alternatives a la castration chirurgicale des porcelets? INRA Prod Anim 2006;19:347-356.
31. Kohler I, Moens Y, Busato A, et al. Inhalation anaesthesia for the castration of piglets: CO2 compared to halothane. Zentralbl Veterinarmed A 1998;45:625-633.
32. Hodgson DS. Comparison of isoflurane and sevoflurane for short-term anesthesia in piglets. Vet Anaesth Analg 2007;34:117-124.
33. Hodgson, S. An inhaler device using liquid injection of isoflurane for short term anesthesia in piglets. Vet Anaesth Analg 2006;33:207-213.
34. Schulz C, Ritzmann M, Palzer A, et al. Changes in the concentration of noradrenaline and adrenaline before and after castration of piglets with and without isoflurane anesthesia. 1: Dtsch Tierarztl Wochenschr. 2007;114:454-459.
35. Rault JL and Lay DC. Nitrous oxide by itself is insufficient to relieve pain due to castration in piglets. J Anim Sci. 2011;89:3318-3325.
36. McGlone JJ and Hellman JM. Local and general anesthesic effects on behavior and performance of two- and seven-week-old castrated and uncastrated piglets. J Anim Sci. 1988 Dec;66(12):3049-58.
37. Jaggin N, Gerber S, Schatzmann U. General anaesthesia, analgesia and pain associated with the castration of newborn piglets. Acta Veterinaria Scandinavica 2006;48:S12
38. Fredriksen B, Nafstad O. Surveyed attitudes, perceptions and practices in Norway regarding use of local anaesthesia in piglet castration. Res Vet Sci 2006;81:293-295.
39. Prunier A, Mounier AM, Hay M. Effects of castration, tooth resection, or tail docking on plasma metabolites and stress hormones in young pigs. J Anim Sci 2005;83:216-222.
40. Haga HA and Ranheim B. Castration of piglets: the analgesia effects of intratesticular and intrafunicular lidocaine injection. Vet Anaesth Analg 2005;32:1-9.
41. Leidig MS, Hertrampf B, Failing K, et al. Pain and discomfort in male piglets during surgical castration with and without local anaesthesia as determined by vocalization and defense behaviour. Appl Anim Behav Sci 2009;116:174-178.
42. Kluivers-Poodt M, Hopster H, Spoolder HAM. 2007. Castration under anaesthesia and/or analgesia in commercial pig production. Report 73, Animal Sciences Group, Wageningen-UR, the Netherlands.
43 Lam M, Haley D, Friendship R et al. The effects of lidocaine and meloxicam on piglets during and post-castration. AASV Proceedings. 2013;44:271(Abstr.).
44. Skarstad GA and Borgen S Norwegian pig producers' view on animal welfare, discussion paper 2007-1, FILF, Oslo, Available at: http://nilf.no/publikasjoner/Discussion_Papers/2007/DP-2007-01.pdf Accessed November 19, 2015.
45. Heinritzi and Ritzmann.  Alternatives for castration of suckling piglets, determination of catecholamines and wound healing after castration of suckling piglets at different points of time. Dtsch Tierarztl Wochenschr. 2006 Mar;113(3):94-7.
46.Hooven, M. Stress remains in spite of expensive shot. Pig Progress 2005;21:10-11.
47. McGlone JJ, Nicholson RI, Hellman JM, et al. The development of pain in young pigs associated with castration and attempts to prevent castration-induced behavioral changes. J Anim Sci 1993;71:1441-1446.
48. Cronin GM, Dunshea FR, Butler KL, et al. The effects of immune- and surgical-castration on the behaviour and consequently growth of group-housed, male finisher pigs. Appl Anim Behav Sci. 2003;81:111-126.
49. Tallet C, Brillout A, Meunier-Salaun MC, et al. Effects of neonatal castration on social behaviour, human-animal relationship and feeding activity in finishing pigs reared in a conventional or an enriched housing. Appl Anim Behav Sci. 2013; In Press http://dx.doi.org/10.1016/j.applanim.2013.03.001
50. http://www.veths.no/upload/SportFaMed/Poster_Archibald%20et%20al_QTL.pdf
51. Hofmo PO. Sperm sorting and low dose insemination in the pig—an update. Acta Vet Scand 2006;48:s11.