Sexual maturity as risk for development of deviant behaviours in pig production systems with entire males

Main Article Content

Dimitar Nakov
Metodija Trajchev
Slavča Hristov
Branislav Stanković
Marko Cincović
Zvonko Zlatanović
Jovan Bojkovski


Male piglets are castrated primarily to avoid the unpleasant boar taint in meat, and additionally for the predisposition of castrates to accumulate fat and for their lower risk of developing unwanted behaviours. There are two main strategies available for withdrawing from surgical castration: one is immunocastration and the other is to raise entire male pigs or boars. Additionally, raising intact boars is more profitable because of the production of carcasses with lean meat and better feed conversion. Boars (compared to castrates) exhibit more aggressive, sexual, damaging social behaviour and reduced feeding behaviour with a lower prevalence of sickness behaviour as a result of good health and low susceptibility to chronic inflammation. In this review, the behaviours specific for boars as a result of sexual maturity are reviewed, with an overview of differences in the behaviour of surgically castrated barrows, immunocastrates and boars reared in group-housed systems. The raising of boars allows for good welfare of these animals in early life, but later, on reaching sexual maturity, the welfare of boars can be diminished because of their propensity to aggression and more mounting behaviour than castrates. Innovations in the breeding and management of boars are needed to improve their performance and to reduce welfare implications of these animals raised in social groups, and in particular to minimize deviant behaviours towards pen mates.


Download data is not yet available.

Article Details

How to Cite
Nakov, D., Trajchev, M., Hristov, S., Stanković, B., Cincović, M., Zlatanović, Z., & Bojkovski, J. (2021). Sexual maturity as risk for development of deviant behaviours in pig production systems with entire males. Veterinarski Glasnik, 75(2), 112-131.


Andersson H. K., Hullberg A., Malmgren L., Lundström K., Rydhmer L., Squires J. 1999. Sexual maturity in entire male pigs: environmental effects, relations to skatole level and female puberty. Acta Agriculturae Scandinavica, Section A 49:103–112.

Andersson H. K., Andersson K., Zamaratskaia G., Rydhmer L., Chen G., Lündstrom K. 2005. Effect of single-sex or mixed rearing and live weight on performance, technological meat quality and sexual maturity in entire male and female pigs fed raw potato starch. Acta Agriculturae Scandinavica, Sect. A 55:80–90.

Andersen I. L., Andenaes H., Bøe K. E., Jensen P. and Bakken M. 2000. The effects of weight asymmetry and resource distribution on aggression in groups of unacquainted pigs. Applied Animal Behaviour Science, 68:107-120.

Averós X., Brossard L., Dourmad J. Y., de Greef K. H., Edge H. L., Edwards S. A., Marie-Christine Meunier-Salaün M. C. 2010. A meta-analysis of the combined effect of housing and environmental enrichment characteristics on the behaviour and performance of pigs. Applied Animal Behaviour Science, 127(3-4):73-85.

Batorek N., Cande-Potokar M., Bonneau M., Van Milgen J. 2012. Meta-analysis of the effect of immunocastration on production performance, reproductive organs and boar taint compounds in pigs. Animal, 6(8):1330-1338.

Berry M. and Signoret J. P. 1984. Sex play and behavioural sexualisation in the pig. Reproduction, Nutrition, Development, 24:507-513. ISSN: 0181-1916.

Bonneau M., Le Denmat M., Vaudelet J. C., Veloso-Nunes J. R., Mortensen A. B., Mortensen H. P. 1992. Contributions of fat androstenone and skatole to boar taint: I. Sensory attributes of fat and pork meat. Livestock Production Science, 32:63-80.

Bonneau M., Kempster A. J., Claus R., Claudi-Magnussen C., Diestre A., Tornberg E., Walstra P., Chevillon P., Weiler U., Cook G. L. 2000. An international study on the importance of androstenone and skatole for boar taint: I. Presentation of the programme and measurement of boar taint compounds with different analytical procedures. Meat Science, 54:251–259. doi:10.1016/S0309-1740(99)00102-3.

Boyle L. A., Bjorklund L. 2007. Effects of fattening boars in mixed or single sex groups and split marketing on pig welfare. Animal Welfare, 16:259-262. ISSN 0962-7286.

Bracke M. B. M., Rodenburg T. B., Vermeer H. M., van Nieker T. G. C. M. 2018. Towards a Common Conceptual Framework and Illustrative Model for Feather Pecking in Poultry and Tail Biting in Pigs–Connecting Science to Solutions. Available online at:

Breuer K., Sutcliffe M. E. M., Mercer J. T., Rance K. A., O’Connell N. E., Sneddon I.A., Edwards S.A. 2005. Heritability of clinical tail-biting and its relation to performance traits. Livestock Production Science, 93,1:87-94.

Brunberg E., Jensen P., Isaksson A., Keeling L. J. 2013. Brain gene expression differences are associated with abnormal tail biting behaviour in pigs. Genes, Brain and Behavior, 12(2): 275–281.

Brunberg E., Rodenburg T. B., Rydhmer L., Kjaer J. B., Jensen P., Keeling L. J. 2016. Omnivores going astray: a review and new synthesis of abnormal behaviour in pigs and laying hens. Frontier in Veterinary Science, 3: 57. doi: 10.3389/fvets.2016.00057.

Rocha L. M., Bridi A. M., Foury A., Mormède P., Weschenfelder A. V., Devillers N., Bertoloni W., Faucitano L. 2013. Effects of ractopamine administration and castration method on the response to preslaughter stress and carcass and meat quality in pigs of two Piétrain genotypes. Journal of Animal Science, 91(8):3965–3977.

Campbell R. G., Taverner M. R. 1988. Genotype and Sex Effects on the Relationship Between Energy Intake and Protein Deposition in Growing Pigs. Journal of Animal Science, 66 (3): 676–686.

Carroll J. A., Berg E. L., Strauch T. A. Roberts M. P., Kattesh H. G. 2006. Hormonal profiles, behavioural responses, and short-term growth performance after castration of pigs at three, six, or 12 days of age. Journal of Animal Science, 84:1271-1278.

CASTRUM 2017. Pig castration: methods of anaesthesia and analgesia for all pigs and other alternatives for pigs used in traditional products. Castrum-study.pdf.

Cronin G. M., Dunshea F. R., Butler K. L., McCauly I., Barnett J. L., Hemsworth P. H. 2003. The effects of immune- and surgical-castration on the behaviour and consequently growth of group-housed, male finisher pigs. Applied Animal Behavior Science, 81: 111-126.

Cross A. J., Keel B. N., Brown-Brandl T. M., Cassady J. P. and Rohrer G. A. 2018. Genome-wide association of changes in swine feeding behaviour due to heat stress. Genetics, Selection, Evolution, 50: 11.

Dantzer R., O’Connor J. C., Freund G. G., Johnason R. W., Kelley K. W. 2008. From inflammation to sickness and depression: when the immune system subjugates the brain. Nature Reviews Neuroscience, 9:46–57. doi: 10.1038/nrn2297.

De Briyne N., Berg C., Blaha T., Temple D. 2016 Pig castration: will the EU manage to ban pig castration by 2018 Porcine Health Management, 2:29.

D’Eath R. B., Roehe R., Turner S. P., Ison S. H., Farish M., Jack M. C., Lawrence A. B. 2009. Genetics of animal temperament: aggressive behaviour at mixing is genetically associated with the response to handling in pigs. Animal, 3(11): 1544–1554.

D’Eath R., Arnott G., Turner, S. P., Jensen T., Lahrmann H. P., Busch M. E., Niemi J. K., Lawrence A. B., Sandoe P. 2014. Injurious tail biting in pigs: how can it be controlled in existing systems without tail docking? Animal, 8:1479–1497. doi: 10.1017/S1751731114001359.

De Kruijf J. M., Welling A. A. 1988 Incidence of chronic inflammations in gilts and castrated boars. Tijdschrift voor Diergeneeskunde 113: 415-417. Dutch. PMID: 3376078.

Einarsson S. 2006. Vaccination against GnRH: Pros and cons. Acta Veterinaria Scandinavica, 48. doi:10.1186/1751‐0147‐48‐S1‐S10.

European Declaration on Alternatives to Surgical Castration of Pigs. Available online:

Faucitano L. 2001. Causes of skin damage to pig carcasses. Canadian Journal of Animal Science, 81:39–45.

Fábrega E., Velarde A., Cros J., Gispert M., Suarez P., Tibau J., Soler J. 2010. Effect of vaccination against gonadotrophin-releasing hormone, using Improvac®, on growth performance, body composition, behaviour and acute phase proteins. Livestock Science, 132(1-3):53-59.

Ford J. J. 1990. Differentiation of sexual behaviour in pigs. Journal of Reproduction and Fertility, Suppl., 40:311-321. PMID: 2192047.

Fraser D. 1984. The role of behaviour in swine production. A review of research. Applied Animal Ethology, 11:317-339.

Fredriksen B., Nafstad O., Lium B. M., Marka C. H., Heier B. T., Andresen O. et al.

Entire male pig production in ‚born-to-finishing-pens’. Project no. 6624.

Norwegian Meat Research Centre.

Fredriksen B., Lium B. M., Marka C. H., Mosveen B., Nafstad O. 2008. Entire male

pigs in farrow-to-finishing pens- effects on animal welfare. Applied Animal

Behaviour Science, 110: 258-268

Fredriksen B., Hexeberg C. 2009. The effect of removing animals for slaughter on the behaviour of the remaining male and female pigs in the pen. Research in Veterinary Science, 86(2):368-370.

Goossens X., Sobry L., Odberg F., Tuyttens F., Maes D., De Smet S., Nevens F., Opsomer G., Lommelen, F., Geers R. 2008. A population-based on-farm evaluation protocol for comparing the welfare of pigs between farms. Animal Welfare, 17:35-41.

Haga H. A., Ranheim B. 2005 Castration of piglets: the analgesic effects of intratesticular or intrafunicular lidocaine injection. Veterinary Anaesthesia and Analgesia, 32:1-9.

Hansson M., Lundelheim N., Nyman G., Johansson G. 2011. Effect of local anaesthesia and/or analgesia on pain responses induced by piglet castration. Acta Veterinaria Scandinavica, 53:34-43.

Hay M., Vulin A., Genin S., Sales P., Prunier A. 2003 Assessment of pain induced by castration in piglets: behavioural and physiological responses over the subsequent 5 days. Applied Animal Behaviour Science, 82:201-218.

Hemsworth P. H., Barnett J. L., Hansen C. 1986. The influence of handling by humans on the behaviour, reproduction and corticosteroids of male and female pigs. Applied Animal Behaviour Science, 15:303–314.

Hemsworth P. H., Barnett J. L., Campbell R. G. 1996. A study of the relative aversiveness of a new daily injection procedure for pigs. Applied Animal Behaviour Science, 49:389-401.

Hemsworth P. H., Tilbrook A. J. 2007. Sexual behaviour of male pigs. Hormones and Behaviour, 52:39-44.

Holinger M., Früh B., Hillmann E. 2015. Group composition for fattening entire male pigs under enriched housing conditions—Influences on behaviour, injuries and boar taint compounds, Applied Animal Behaviour Science, 165:47-56.

Hristov S. V., Stanković B. M., Ostojić Andrić D. N., Nevena Lj. Maksimović N. Lj., Nakov D. D. 2019. The most important dilemmas regarding the welfare of farm animals. Journal of Agricultural Sciences, 64(4):319-340.

Leidig M. S., Hertrampf B., Failing K., Schumann A., Reiner G. 2009. Pain and discomfort in male piglets during surgical castration with and without local anaesthesia as determined by vocalization and defence behaviour. Applied Animal Behaviour Science, 116:174–178.

Llamas Moya S, Boyle L. A., Lynch B. P., Arkins S. 2008. Effect of surgical castration on the behavioural and acute phase responses of 5-day-old piglets. Applied Animal Behaviour Science, 111:133–145.

Marchant-Forde J. N., Lay Jr. D. C., McMunn K .A., Cheng H. W., Pajor E. A., Marchant-Forde R. M. 2009. Postnatal piglet husbandry practices and well-being: the effects of alternative techniques delivered separately. Journal of Animal Science, 87:1479–1492.

Marx G., Horn T., Thielebein J., Knubel B., von Borell E. 2003. Analysis of pain-related vocalization in young pigs. Journal of Sound and Vibration, 266:687-698

Munsterhjelm C., Nordgreen J., Aae F., Heinonen M., Valros A., Janczak A. M. 2019. Sick and grumpy: changes in social behaviour after a controlled immune stimulation in group-housed gilts. Physiology and Behavior, 198:76–83.

Nakov D., Hristov S., Stankovic B., Pol F., Dimitrov I., Ilieski V., Mormede P., Hervé J., Terenina E., Lieubeau B., Papanastasiou D. K., Bartzanas T., Norton T., Piette D., Tullo E., van Dixhoorn, I. D. E. 2019. Review: Methodologies for assessing disease tolerance in pigs. Frontiers in Veterinary Science, 5:329. doi: 10.3389/fvets.2018.00329.

Nordgreen J., Edwards S. A., Boyle L. A., Bolhuis J. E., Veit C., Sayyari A., Marin D. E., Dimitrov I., Janczak A. M., Valros A. 2020. A Proposed Role for Pro-Inflammatory Cytokines in Damaging Behaviour in Pigs. Frontiers in Veterinary Science, 7:646.

Oliver M. A., Mirabito L., Veissier I., Thomas C., Bonneau M., Doran O.,

Tacken G., Backus G., Cozzi G., Knierim U., Pentelescu O. N. 2008. ALCASDE - final report. Study on the improved methods for animal friendly production, in particular on the alternatives to castration in pigs and to de-horning in cattle. SANCO/2008/D5/018.

Parois S., Larzul C., Prunier A. 2017. Associations between the dominance status and sexual development, skin lesions or feeding behaviour of intact male pigs. Applied Animal Behaviour Science, 187:15–22.

Patterson R. L. S. 1982. Effect of season upon 5a-androstenone (boar taint) concentrations in the subcutaneous fat of commercial weight boars. Journal of the Science of Food and Agriculture, 33:55–58.

Patterson R. L. S., Lightfoot A. L. 1984. Effect of sex grouping during growth on 5-androstenone development in boars at three commercial slaughter weights. Meat Science, 10:253–263.

Prunier A., Mounier A. M., Hay M. 2005. Effects of castration, tooth resection or tail docking on plasma metabolites and stress hormones in young pigs. Journal of Animal Science, 83:216-222.

Prunier A., Bonneau M., von Borell E. H., Cinotti S., Gunn M., Fredriksen B., Giersing M., Morton D. B., Tuyttens F. A. M., Velarde A. 2006. A review of the welfare consequences of surgical castration in piglets and the evaluation of non-surgical methods. Animal Welfare, 15:277-289.

Prunier A., Averos X., Dimitrov I., Edwards S. A., Hillmann E., Holinger M., Ilieski V., Leming R., Tallet C., Turner S. P., Zupan M., Camerlink I. 2019. Early life predisposing factors for tail biting in pigs. Animal, 14:1–18.

Prunier A., Devillers N., Herskin M. S., Sandercock D. A., Sinclair A. R. L., Tallet C., von Borell E. 2020. Husbandry interventions in suckling piglets, painful consequences and mitigation. In C. Farmer (Ed.), The Suckling and Weaned Piglet (pp. 107-138). Wageningen Academic Publishers.

Puls C. L., Rojo A., Matzat P. D., Schroeder A. L., Ellis M. 2017. Behaviour of immunologically castrated barrows in comparison to gilts, physically castrated barrows, and intact male pigs. Journal of Animal Science, 95:2345–2353.

Puppe B., Schon P. C., Tuchscherer A., Manteuffel G. 2005. Castration-induced vocalization in domestic piglets, Sus scrofa: complex and specific alteration of the vocal quality. Applied Animal Behavior Science, 95:67-78.

Quiniou N., Monziols M., Colin F., Goues T., Courboulay V. 2012. Effect of feed restriction on the performance and behaviour of pigs immunologically castrated with Improvac®. Animal, 6(9):1420-1426.

Reiter S., Zöls S., Ritzmann M., Stefanski V., Weiler U. 2017. Penile Injuries in Immunocastrated and Entire Male Pigs of One Fattening Farm. Animals, 7:71.

Rizvi S., Nicol C. J., Green L. E. 1998. Risk factors for vulva biting in breeding sows in south-west England. Veterinary Record, 143:654.

Rizvi S., Nicol C. J., Green L. E. 2000. A descriptive survey of the range of injuries sustained and farmers’ attitudes to vulva biting in breeding sows in South-West England. Animal Welfare, 9:273–280.

Robert S., Passillé A., St. Pierre N., Pelletier G., Petitclerc D., Dubreuil P., Brazeau P. 1989. Effect of the stress of injections on the serum concentration of cortisol, prolactin, and growth hormone in gilts and lactating sows. The Canadian Journal of Animal Science, 69:663–672.

Rohrer G. A., Brown-Brandl T., Rempel L. A., Schneider J. F., Holl J. 2013. Genetic analysis of behaviour traits in swine production. Livestock Science, 157:28–37.

Rydhmer L., Zamaratskaia G., Andersson H. K., Algers B., Guillemet R., Lundstrom K. 2006. Aggressive and sexual behaviour of pigs raised without castration. Acta Agricultura Scandinavica, section A, Animal science, 56:109-119.

Rydhmer L., Lundstrom K., Andersson K. 2010. Immunocastration reduces aggressive and sexual behaviour in male pigs. Animal, 4(6):965-972.

Salmon E., Edwards S. 2006. Effects of gender contact on the behaviour and performance of entire boars and gilts from 60-130 kg. Proceedings British Society of Animal Science, 72.

Santos R. K. S., Caldara F. R., Moi M., Santos L. S., Nääs I. A., Foppa L., Rodrigo Garófallo Garcia R. G., Raul R., Borquis A. 2016. Behaviour of immunocastrated pigs. Revista Brasileira de Zootecnia, 45(9): 540-545,

Schmidt T., Calabrese J. M., Grodzycki M., Paulick M., Pearce M. C., Rau F., von Borell E. 2011. Impact of single-sex and mixed-sex group housing of boars vaccinated against GmRF or physically castrated on body lesions, feeding behaviour and weight gain. Applied Animal Behaviour Science, 130:42-52.

Schroder-Petersen D. L., Simonsen H. B. 2001. Tail biting in pigs, The Veterinary Journal, 162:196-210.

Skrlep M., Tomaševic I., Mörlein D., Novakovic S., Egea M., Garrido M. D., Linares M. B., Peñaranda I., Marijke Aluwé M., Font-i-Furnols M. 2020. The Use of Pork from Entire Male and Immunocastrated Pigs for Meat Products-An Overview with Recommendations. Animals, 10:1754.

Sutherland M. A., Davis B. L., Brooks T. A., McGlone J. J. 2010. Physiology and behaviour of pigs before and after castration: Effects of two topical anesthetics. Animal, 4:2071–2079.

Sutherland M. A., Davis B. L., Brooks T. A., Coetzee J. F. 2012. The physiological and behavioural response of pigs castrated with and without anesthesia or analgesia. The Journal of Animal Science, 90:2211–2221.

Taylor A. A., Weary D. M., Lessard M., Braithwaite L. A. 2001. Behavioural responses of piglets to castration: the effect of pig age. Applied Animal Behaviour Science, 73:35-45.

Taylor N. R., Parker R. M. A., Mendl M., Edwards S. A., Main D. C. J. 2012. Prevalence of risk factors for tail biting on commercial farms and intervention strategies. The Veterinary Journal, 194:77–83. doi: 10.1016/j.tvjl.2012.03.004.

Tomasevic I., Bahelka I., Čandek-Potokar M., Čítek J., Djekić I., Getya A., Guerrero L., Iordachescu G., Ivanova S., Kušec G., Nakov D., Solowiej B., Szabó C., Tudoreanu L., Weiler U., Font i Furnols M. 2020a. Attitudes and beliefs of Eastern European consumers about piglet castration and meat from castrated pigs. Meat Science, 160: 107965.

Tomasevic I., Bahelka I., Čandek-Potokar M., Čítek J., Djekić I., Getya A., Guerrero L., Ivanova S., Kušec G., Nakov D., Solowiej B., Stoica M., Szabó C., Tudoreanu L., Weiler U., Font i Furnols M. 2020b. Attitudes and beliefs of Eastern European consumers towards animal welfare. Animals, 10:1220.

Trajcev M., Nakov D. 2009. Piglet welfare and behaviour in different heating systems in farrowing house. Macedonian Veterinary Review, 32(2):33-44.

Weiler U., Bonneau M. 2019. Why it is so difficult to end surgical castration of boars in Europe: Pros and cons of alternatives to piglet castration. IOP Conf. Ser.: Earth Environ. Sci. 333:012001. doi:10.1088/1755-1315/333/1/012001.

Valros A., Munsterhjelm C., Hänninen L., Kauppinen T., Heinonen M. 2016. Managing undocked pigs – on-farm prevention of tail biting and attitudes towards tail biting and docking. Porcine Health Management, 2:2.

Vanheukelom V., Van Beirendonck S., Van Thielen J., Bert Driessen B. 2012. Behaviour, production results and meat quality of intact boars and gilts housed in unmixed groups: A comparative study. Applied Animal Behaviour Science, 142:154 - 159

van Putten G. 1969. An Investigation into tail-biting among fattening pigs. British Veterinary Journal, 125:511–517.

van Staaveren N., Calderón Díaz J. A., Garcia Manzanilla E., Hanlon A., Boyle L. A. 2018. Prevalence of welfare outcomes in the weaner and finisher stages of the production cycle on 31 Irish pig farms. Irish Veterinary Journal, 71:9.

von Borell E., Bonneau M., Holinger M., Armelle Prunier A., Stefanski V., Zöls S., Weiler U. 2020. Welfare aspects of raising entire male pigs and immunocastrates Animals, 10, 2140.

Velarde A., Gispert M., Oliver M. A., Soler J., Tibau J., Fabrega E. 2007. The effect of immunocastration on the behaviour of pigs. In Proceedings of the 41st International Congress of the International Society for Applied Ethology, 8–12 August 2007, pp. 117. Merida, Mexico.

Vargas L., Sewell R., Marshall A., Galatioto J., Tsang Y. Y., Catterall J. F., Hunnicut G. R. 2005. Immune complex deposition in adult male Sprague-Dawley rats chronically immunized with GnRH. American Journal of Reproductive Immunology. 54: 292-310.

Wallenbeck A., Keeling L. J. 2013. Using data from electronic feeders on visit frequency and feed consumption to indicate tail biting outbreaks in commercial pig production. Journal of Animal Science, 91:2879–2884.

Walker N. 1978. Boars for meat production – the effect of single-sex or mixed-sex groups on growth performance and carcass characteristics. Record of Agricultural Research (UK), 26: 7–10.

Wariss P. D. 2000. Optimal lairage times and conditions for slaughter pigs: a review. Veterinary Record, 153(6): 170−176.

Weary D. M., Fraser D. 1999. Partial tooth-clipping of suckling pigs: effects on neonatal competition and facial injuries. Applied Animal Behavior Science, 65:21-27.

Weiler U., Isernhagen M., Stefanski V., Ritzmann M., Kress K., Hein C., Zols S. 2016. Penile Injuries in Wild and Domestic Pigs. Animals (Basel), 6.

Zamaratskaia G., Rydhmer L., Andersson H. K., Chen G., Lowagie S., Andersson K., Lundstrom K. 2008. Long-term effect of vaccination against gonadotropin releasing hormone, using Improvac TM, on hormonal profile and behaviour of male pigs. Animal Reproduction Science, 108:37–48.

Zamaratskaiaa G., Rasmussen M. K. 2015. Immunocastration of male pigs – situation today. Procedia Food Science, 5:324-327.

Most read articles by the same author(s)