An adult bird which has been beak-trimmed as a chick

Debeaking, beak trimming (also spelt beak-trimming[1]), or beak conditioning is the partial removal of the beak of poultry, especially layer hens and turkeys although it may also be performed on quail and ducks. Most commonly, the beak is shortened permanently, although regrowth can occur. The trimmed lower beak is somewhat longer than the upper beak. A similar but separate practice, usually performed by an avian veterinarian or an experienced birdkeeper, involves clipping, filing or sanding the beaks of captive birds for health purposes – in order to correct or temporarily to alleviate overgrowths or deformities and better allow the bird to go about its normal feeding and preening activities.[2] Amongst raptor-keepers, this practice is commonly known as "coping".[3]

Beak trimming is most common in egg-laying strains of chickens. In some countries, such as the United States, turkeys routinely have their beaks trimmed. In the UK, only 10% of turkeys are beak trimmed.[4] Beak trimming is a preventive measure to reduce damage caused by injurious pecking such as cannibalism, feather pecking and vent pecking, and thereby improve livability.[5] Commercial broiler chickens are not routinely beak trimmed as they reach slaughter weight at approximately 6 weeks of age, i.e. before injurious pecking usually begins. However, broiler breeding stock may be trimmed to prevent damage during mating.[6] In some countries, beak trimming is done as a last resort where alternatives are considered not to be possible or appropriate.

Opponents of beak trimming state that the practice reduces problem pecking by minor amounts compared to the trauma, injury, and harm done to the entire flock by beak trimming. Reduction is in single digit percentiles, whereas improvement of conditions especially in layer colonies will cease problematic behavior entirely.[7]

Several European countries have banned beak trimming, including Denmark (2013), Finland (1986), Germany (2017),[7] the Netherlands (2019),[8] Norway (1974) and Sweden (1988); analysts expect other European countries such as the UK to follow in the near future.[9][10]

In close confinement, cannibalism, feather pecking and aggression are common among turkeys, ducks, pheasants, quail, and chickens of many breeds (including both heritage breeds and modern hybrids) kept for eggs. The tendency to cannibalism and feather pecking varies among different strains of chickens, but does not manifest itself consistently. Some flocks of the same breed may be entirely free from cannibalism, while others, under the same management, may have a serious outbreak. Mortalities, mainly due to cannibalism, can be up to 15% in egg laying flocks housed in aviaries,[11] straw yards,[12] and free-range systems.[13]

Because egg laying strains of chickens can be kept in smaller group sizes in caged systems, cannibalism is reduced[14][15] leading to a lowered trend in mortality as compared to non-cage systems. Cannibalism among flocks is highly variable and when it is not problematic, then mortalities among production systems are similar.[14]

History

Beak trimming was developed at the Ohio Agricultural Experiment Station in the 1930s.[16] The original technique was temporary, cutting approximately 6 mm (1/4 inch) off the beak. It was thought that the tip of the beak had no blood supply and presumably no sensation. The procedure was performed by hand with a sharp knife, either when deaths due to cannibalism became excessive, or when the problem was anticipated because of a history of cannibalism in the particular strain of chicken.

Cannibalism is a serious management problem dating back to the periods before intensive housing of poultry became popular. Poultry books written before vertical integration of the poultry industry describe the abnormal pecking of poultry:

Chicks and adult birds' picking at each other until blood shows and then destroying one another by further picking is a source of great loss in many flocks, especially when kept in confinement .... The recommendation of the Ohio Experiment Station of cutting back the tip of the upper beak has been found to be effective until the beak grows out again.[17]

Cannibalism has two peaks in the life of a chicken; during the brooding period and at the onset of egg laying. The point-of-lay cannibalism is generally the most damaging and gets most of the attention. The temporary beak trimming developed at the Ohio Experiment Station assumed that cannibalism was a phase, and that blunting the beak temporarily would be adequate.

Current methods and guidelines

In recent years, the aim has been to develop more permanent beak trimming (although repeat trimming may be required), using electrically heated blades in a beak trimming machine, to provide a self-cauterizing cut. There are currently (2012) four widely used methods of beak trimming: hot blade, cold blade (including scissors or secateurs), electrical (the Bio-beaker) and infrared. The latter two methods usually remove only the tip of the beak and do not leave an open wound; therefore they may offer improvements in welfare. Other approaches such as the use of lasers, freeze drying and chemical retardation have been investigated but are not in widespread use.[18] The infrared method directs a strong source of heat into the inner tissue of the beak and after a few weeks, the tip of the upper and lower beak dies and drops off making the beak shorter with blunt tips. The Bio-beaker, which uses an electric current to burn a small hole in the upper beak, is the preferred method for trimming the beaks of turkeys.[19] The Farm Animal Welfare Council (FAWC) wrote regarding beak trimming of turkeys that cold cutting was the most accurate method, but that substantial re-growth of the beak occurred; although the Bio-beaker limited beak re-growth, it was less accurate. It was considered that the hot cut was the most distressing procedure for turkeys.[4]

In the UK, beak trimming of layer hens normally occurs at 1-day of age at the same time as the chick is being sexed and vaccinated.

USA's UEP guidelines suggest that in egg laying strains of chickens, the length of the upper beak distal from the nostrils that remains following trimming, should be 2 to 3 mm.[20] In the UK, the Farm Animal Welfare Council stated: "The accepted procedure is to remove not more than one third of the upper and lower beaks or not more than one third of the upper beak only" but went on to recommend: "Where beak trimming is carried out, it should, wherever possible, be restricted to beak tipping; that is the blunting of the beak to remove the sharp point which can be the cause of the most severe damage to other birds."[21]

Legislation

Laws regarding beak trimming around the world:
  Nationwide ban on beak trimming
  Some subnational bans on beak trimming
  Beak trimming legal
  No data

There is a trend towards prohibition of beak trimming in Europe over the course of decades. Analysts expect the practice to be gradually banned across the continent.[9][10]

EU law allows member states to debeak poultry according to two regulations: Directive 1999/74/EC for laying hens allows beak trimming, while Directive 2007/43/EC for broilers permits beak trimming only in certain cases.[10] As of April 2019, 80% of laying hens in the EU were estimated to be beak-trimmed.[10]

Country Legal? Since Notes
 AustraliaPartialIllegal in ACT; Vic and NSW considering a ban[22][23]
 AustriaNo2000[24]
 BelgiumYes–Regulated, considering a ban[9]
 CanadaYes–Regulated[25]
 ChinaYes–Unregulated[26]
 DenmarkNo2013–4[24]
 FinlandNo1986[24]
 FranceYes–Regulated[27]
 GermanyNo2017[7]
 LuxembourgYes–Regulated, considering a ban[9]
 NetherlandsNo2019[8]Banned since 1 January 2019.[8]
 New ZealandYes–Regulated[28]: 24 
 NorwayNo1974[24]
 SwedenNo1988[24]
  SwitzerlandYes–Regulated, considering a ban[9]
 United KingdomYes–Regulated, considering a ban[9][10][24]
 United StatesYes–Regulated[29]

Australia

As of July 2019, beak trimming is only banned in the Australian Capital Territory by means of the Animal Welfare Act 1992 (ACT) s 9C.[30] It is currently debated in parliament whether debeaking should be banned in Victoria and New South Wales.[22][23] A 2019 Voiceless report recommended the NSW Parliament to prohibit debeaking and instead '[introduce] enriched environmental conditions, such as litter and suitable range areas [to] encourage interaction and mental stimulation for hens. Better nutrition, lighting and parasite management may also help reduce injurious pecking.'[30] In a 2015 survey conducted by the Humane Society International Australia, 91% of respondents stated that free range egg boxes should display whether the hens had undergone beak trimming.[31]

Canada

Beak trimming is legal but regulated in Canada. The National Farm Animal Care Council's 2016 Poultry Code of Practice urges to 'make every effort to manage breeders so that physical alterations, such as beak trimming, are not necessary'; should it prove necessary, however, infrared treatment is recommended over hot blade treatment.[25]

China

There are no regulations on beak trimming in the People's Republic of China. Some companies have decided to voluntarily phase out debeaking, such as Ningxia Xiaoming Farming and Animal Husbandry Co. Ltd.[26]

France

In France, clipping beaks of poultry chickens is authorised only when it preserves the health and wellbeing of animals, meaning to limit the risks of cannibalism and pecking.[27] It is only authorised on chicks less than 10 days old intended for laying eggs and must be carried out by qualified personnel. It can therefore be carried out by breeders and agricultural workers.[32]

Germany

Agriculture Minister Christian Meyer announced that Germany would phase out beak trimming by 2017 due to animal welfare concerns.[7]

Netherlands

A ban on beak trimming in the Netherlands was first announced in 1996, but due to objections from the poultry sector it was delayed for years.[33] In June 2013, the government struck an agreement between poultry farmers and animal welfare groups to phase out debeaking and prohibit it in 2018.[34] The prohibition on trimming eventually went into effect on 1 January 2019.[8]

New Zealand

Beak trimming, officially known as 'beak tipping' in law, is legal but regulated in New Zealand. The Layer Hens Code of Welfare (last updated 1 October 2018) notes that the National Animal Welfare Advisory Committee (NAWAC) 'encourages the industry to develop management systems to protect against all forms of injurious pecking without the need for beak tipping'. The Code recommends that '[a]lternative strategies for managing injurious (feather) pecking that minimise the need for beak tipping should be employed e.g. use and availability of different foraging resources.' In case that beak tipping is deemed necessary, however, it requires competent trained operators, must be carried out within 3 days of hatching (except in emergencies under veterinary supervision) and may not remove more than one-quarter of the upper or lower beaks.[28]: 24 

Nordic countries

Norway was the first country in the world to outlaw beak trimming in 1974, followed by Finland in 1986 and Sweden in 1988.[24]: 3  Beak trimming was subsequently phased out in Denmark in two stages: in 2013 for the enriched cage system and in 2014 for aviary and free range systems.[24]: 21 

Switzerland

Beak trimming in Switzerland is legal but regulated; it is expected that the practice will be prohibited in the near future.[9] Although the use of cages for layer hens was prohibited in 1992, by 2000 still 59% of flocks (61% of hens) was still debeaked.[35]

United Kingdom

Beak trimming is legal but regulated in the UK; it is expected that the practice will be prohibited in the near future.[9][10] In 2011, the British government set up the Beak Trimming Action Group (BTAG) to review the matter with representatives from different stakeholders, including the industry, the government, animal welfare groups and veterinarians. A late 2015 BTAG report endorsed by Farming Minister George Eustice concluded that banning it in January 2016 would be too early as the sector needed more time to change its management techniques in order to avoid feather pecking, but that beak trimming should be phased out in the future.[36] Laying Hen Welfare Forum chairman Andrew Joret stated in March 2020: 'A ban is coming. In my opinion, we have five years at most to prepare for this. We need to work out ways of keeping birds well-feathered, and if we can, eventually do that without beak trimming.'[37]

United States

Beak trimming is legal in the United States, but there are some regulations: producers need to have a beak-trimming policy, it may not be employed to improve feed efficiency, but may be used to prevent cannibalism.[29] Humane Society vice president Paul Shapiro claimed that birds only resort to cannibalism when they are confined and have nothing to do.[29]

Costs and benefits

Costs

The costs of beak trimming relate primarily to welfare concerns. These include acute stress, and acute, possibly chronic, pain following trimming. A bird's ability to consume food is impaired following beak trimming because of the new beak shape and pain. Most studies report reduced body weights and feed intake following beak trimming; however, by sexual maturity or peak egg production, growth rates are usually normal.[5][38][39] Weight losses were reduced in chicks that were beak trimmed by infrared compared with chicks trimmed by a hot-blade.[40]

Pain of beak trimming

White Leghorn pullets showing the results of beak trimming
Non-beak trimmed
Beak trimmed

Whether beak trimming causes pain is a hotly debated concern. It is a complex issue as it may involve acute and/or chronic pain, and depends on the age it is performed, the method of trimming and the length of beak that is removed. Beak trimming in the poultry industry usually occurs without anaesthetic at 1-day of age or when the chicks are very young, but can occur at a later age if an outbreak of feather pecking occurs, and in some cases, birds may be beak trimmed on repeated occasions. Beak trimming is not permitted in the UK on meat chickens that are aged over 10 days.[41]

Acute pain

The beak is a complex, functional organ with an extensive nervous supply including nociceptors that sense pain and noxious stimuli.[42][43] These would almost certainly be stimulated during beak trimming, indicating strongly that acute pain would be experienced. Behavioural evidence of pain after beak trimming in layer hen chicks has been based on the observed reduction in pecking behavior, reduced activity and social behavior, and increased sleep duration.[44][45][46][47]

In Japanese quail, beak-trimming by cauterization caused lower body weights and feed intake in the period just after beak trimming.[39] Beak trimmed Muscovy ducks spent less time engaging in beak-related behaviours (preening, feeding, drinking, exploratory pecking) and more time resting than non-trimmed ducks in the days immediately post-trim. These differences disappeared by 1 week post-trim. At 1 week post-trim the trimmed ducks weighed less than non-trimmed ducks, but this difference disappeared by 2 weeks post-trim.[38] It is, however, unclear if the above changes in behaviour arise from pain or from a loss of sensitivity in the beak.[48]

Pecking force has been found to decrease after beak trimming in adult hens,[49] possibly indicating that hens are protecting a painful area from further stimulation. However, pecking force did not differ between chicks with or without minor beak-trims at 2 to 9 days of age, suggesting that chicks with minor beak-trims do not experience pain from the beak.[50]

Chronic pain

Severe beak trimming or beak trimming birds at an older age is thought to cause chronic pain. Following beak trimming of older or adult hens, the nociceptors in the beak stump show abnormal patterns of neural discharge, which indicate acute pain.[42][51][52][53] Neuromas, tangled masses of swollen regenerating axon sprouts,[54] are found in the healed stumps of birds beak trimmed at 5 weeks of age or older and in severely beak trimmed birds.[55] Neuromas have been associated with phantom pain in human amputees and have therefore been linked to chronic pain in beak trimmed birds. If beak trimming is severe because of improper procedure or done in older birds, the neuromas will persist which suggests that beak trimmed older birds experience chronic pain, although this has been debated.[56]

Benefits

The benefits of beak trimming are mainly welfare advantages for birds kept in close confinement, some of which directly relate to increases (or reduced decreases) in production. These include reduced feather pecking and cannibalism, better feathering (though they find it hard to preen with shortened beaks, which means they are not cleaning themselves well), less fearfulness and nervousness, less chronic stress, and decreased mortality.[5][57]

Alternatives

A range of options have been proposed as possible alternatives to beak trimming including modifying the genetics of domesticated poultry to reduce cannibalistic tendencies. For confined housing where light control is possible, lowering light intensity so that birds cannot see each other as easily reduces antagonistic encounters and aggressive behaviour. Enrichment devices, introduced at an early age, such as simple objects hung in a habitat, can reduce aggressive behavior. Dividing the population into smaller group sizes reduces cannibalism. Proper body weight management that avoids underweight pullets reduces the probability of underweight pullets with uterine prolapse that leads to cloacal cannibalism.[19]

See also

References

Wikimedia Commons has media related to Debeaking.
  1. ↑ Zoe Williams (9 March 2020). "Beak-trimming and brutality: is it time to stop buying brown eggs?". The Guardian. Retrieved 19 May 2020.
  2. ↑ "Bird Beaks: Anatomy, Care, and Diseases". Veterinary & Aquatic Services Department, Drs. Foster & Smith. Archived from the original on 4 June 2012. Retrieved 16 April 2012.
  3. ↑ Ash, Lydia. "Coping your Raptor". The Modern Apprentice. Retrieved 16 April 2012.
  4. 1 2 "Beak-trimming". Archived from the original on 2011-11-30. Retrieved 2011-11-11.
  5. 1 2 3 Hester, P.Y. and Shea-Moore, M., (2003). Beak trimming egg-laying strains of chickens. World’s Poultry Science Journal, 59: 458-474
  6. ↑ Gentle, M.J. and McKeegan, D.E.F., (2007). Evaluation of the effects of infrared beak trimming in broiler breeder chicks. Veterinary Record, 160: 145–148
  7. 1 2 3 4 "Ab 2017 bleibt der Schnabel jetzt bundesweit dran!". Archived from the original on 2015-04-14. Retrieved 2016-02-24.
  8. 1 2 3 4 Gemma Venhuizen (7 December 2018). "Hoe gevoelig is de snavel van een vogel?". NRC Handelsblad (in Dutch). Retrieved 18 May 2020.
  9. 1 2 3 4 5 6 7 8 Sandilands, Victoria; Hocking, Paul M. (2012). Alternative Systems for Poultry: Health, Welfare and Productivity. London: CABI. p. 213. ISBN 9781845938246. Retrieved 19 May 2020.
  10. 1 2 3 4 5 6 Melanie Epp (5 April 2019). "Beak trimming trends". Canadian Poultry Magazine. Retrieved 19 May 2020.
  11. ↑ Hill, J.A., (1986). Egg production in alternative systems - a review of recent research in the UK. Research and Development in Agriculture, 3: 13-18
  12. ↑ Gibson, S.W., Dun, P. and Hughes, B.O., (1988). The performance and behaviour of laying fowls in a covered strawyard system. Research and Development in Agriculture, 5: 153-163
  13. ↑ Keeling, L.J., Hughes, B.O. and Dun P., (1988). Performance of free range laying hens in a polythene house and their behaviour on range. Farm Building Progress, 94: 21-28
  14. 1 2 Appleby, M.C. and Hughes B.O., (1991). Welfare of laying hens in cages and alternative systems: Environmental, physical and behavioural aspects. World's Poultry Science Journal, 47: 109-128
  15. ↑ Abrahamsson, P. and Tauson, R., (1995). Aviary systems and conventional cages for laying hens - effects on production, egg quality, health and bird location in 3 hybrids. Acta Agriculturae Scandinavica Section A-Animal Science, 45: 191-203
  16. ↑ Kennard, D.C. (1937). Chicken Vices. 184. Ohio Agricultural Experiment Station. 22: 33-39.
  17. ↑ Jull, M.A., (1938). Poultry Husbandry, 2nd Edition. McGraw Hill, New York., page 346.
  18. ↑ AVMA (2010). "AVMA Literature review on the welfare implications of beaktrimming" (PDF). Retrieved November 23, 2015.
  19. 1 2 Glatz, P.C., (2005). Poultry Welfare Issues: Beak Trimming. Nottingham University Press, Nottingham, United Kingdom.
  20. ↑ United Egg Producers Animal Husbandry Guidelines for U.S. Egg Laying Flocks, 2008
  21. ↑ "FAWC opinion on beak trimming, 2007" (PDF). Archived from the original (PDF) on 27 September 2011. Retrieved 11 November 2011.
  22. 1 2 "Animal law in the spotlight: Victoria's factory farming bill". Archived from the original on 2019-03-31. Retrieved 2015-08-09.
  23. 1 2 "Animal law in the spotlight: NSW battery hen bill". Archived from the original on 2019-03-28. Retrieved 2015-08-09.
  24. 1 2 3 4 5 6 7 8 Anaëlle Laravoire (2016). "Status of beak trimming in EU" (PDF). Danish Poultry Congress 2016. Barn Health. Archived from the original (PDF) on 3 May 2019. Retrieved 18 May 2020.
  25. 1 2 "Code of Practice for the Care and Handling of Hatching Eggs, Breeders, Chicken and Turkeys". National Farm Animal Care Council. 2016. Retrieved 19 May 2020.
  26. 1 2 "How China's Chickens are Going to Lay a Billion Eggs a Day". Voice of America. 9 July 2018. Retrieved 19 May 2020.
  27. 1 2 "Arrêté du 1er février 2002 établissant les normes minimales relatives à la protection des poules pondeuses". www.legifrance.gouv.fr (in French). Legifrance. Retrieved 24 April 2019.
  28. 1 2 "Layer Hens Code of Welfare". Ministry for Primary Industries website. New Zealand Government. 1 October 2018. Archived from the original on 18 February 2021. Retrieved 19 May 2020.
  29. 1 2 3 Tom Philpott (27 September 2014). "Butterball Goes "Humane" for Thanksgiving. Really?". Mother Jones. Retrieved 19 May 2020.
  30. 1 2 "Inquiry into use of battery cages for hens in the egg production industry" (PDF). Submission No 384 to the Parliament of New South Wales. Parliament of New South Wales. 22 July 2019. Retrieved 19 May 2020.
  31. ↑ Humane Society International, Submission to the Australian Treasury, Inquiry into Free Range Egg Labelling, 29 October 2015, 6.
  32. ↑ "Arrêté du 5 octobre 2011 fixant la liste des actes de médecine ou de chirurgie des animaux que peuvent réaliser certaines personnes n'ayant pas la qualité de vétérinaire" (in French). Retrieved 24 April 2019.
  33. ↑ "'Als kippen bloed zien, worden ze gek'". RTL Nieuws (in Dutch). 9 June 2013. Retrieved 19 May 2020.
  34. ↑ "Knippen kipsnavel in 2018 verboden". NOS (in Dutch). 9 June 2013. Retrieved 19 May 2020.
  35. ↑ Grandin, Temple (2015). Improving Animal Welfare, 2nd Edition: A Practical Approach. London: CABI. p. 118. ISBN 9781780644677. Retrieved 19 May 2020.
  36. ↑ Alice Mitchell (26 November 2015). "UK Government Rejects 2016 Beak Trimming Ban". The Poulty Site. Retrieved 19 May 2020.
  37. ↑ Debbie James (28 March 2020). "8 management tips to help prevent severe feather pecking". Farmers Weekly. Mark Allen Group. Retrieved 19 May 2020.
  38. 1 2 Gustafson, L.A., Cheng, H.W., Garner, J.P., Pajor, E.A. and Mench, J.A., (2007). Effects of bill-trimming Muscovy ducks on behavior, body weight gain, and bill morphopathology. Applied Animal Behaviour Science, 103: 59-74
  39. 1 2 Lagana, C., Pizzolante, C.C., Togashi, C.K., Kakimoto, S.K., Saldanha, E.S.P.B. and Alvares, V., (2011). Beak trimming method and drinking system and their effect on the performance and egg quality of Japanese quails. Revista Brasileira de Zootecnia-Brazilian Journal of Animal Science, 40: 1217-1221
  40. ↑ Marchant-Forde, R.M. and Cheng, H.W., (2011). Different effects of infrared and one-half hot blade beak trimming on beak topography and growth. Poultry Science, 89: 2559-2564. doi:10.3382/ps.2010-00890
  41. ↑ Defra. "Guidance on keeping of Chickens" (PDF).
  42. 1 2 Breward, J., (1984). Cutaneous nociceptors in the chicken beak. Proceedings of the Journal of Physiology, London 346: 56
  43. ↑ Gentle, M.J., (1992). Pain in birds. Animal Welfare, 1: 235-247
  44. ↑ Gentle M.J., Hughes B.O. and Hubrecht R.C., (1982). The effect of beak-trimming on food-intake, feeding behaviour and body weight in adult hens. Applied Animal Ethology, 8: 147–157
  45. ↑ Duncan I.J.H., Slee G.S., Seawright E. and Breward J., (1989). Behavioural consequences of partial beak amputation (beak trimming) in poultry. British Poultry Science, 30: 479–488
  46. ↑ Gentle M.J., Hunter L.N. and Waddington D., (1991). The onset of pain related behaviours following partial beak amputation in the chicken. Neuroscience Letters, 128: 113–116
  47. ↑ Gentle, M.J., Hughes, B.O., Fox, A. and Waddington, D., (1997). Behavioural and anatomical consequences of two beak trimming methods in 1- and 10-d-old domestic chicks. British Poultry Science, 38: 453-463
  48. ↑ Hughes, B.O. and Gentle, M.J., (1995). Beak trimming in poultry: Its implications for welfare. World’s Poultry Science Journal, 51: 51–61
  49. ↑ Freire, R., Glatz, P. and Hinch, G., (2008). Self-administration of an analgesic does not alleviate pain in beak trimmed chickens. Asian-Australasian Journal of Animal Science, 21: 443–448
  50. ↑ Freire, R., Eastwood, M.A. and Joyce, M., (2011). Minor beak trimming in chickens leads to loss of mechanoreception and magnetoreception. Journal Animal Science, 89: 1201-1206
  51. ↑ Breward, J., (1985). An Electrophysiological Investigation of the Effects of Beak Trimming in the Domestic Fowl (Gallus gallus domesticus). Ph.D. thesis, University of Edinburgh.
  52. ↑ Gentle, M.J., (1986). Beak trimming in poultry. World’s Poultry Science Journal', 42: 268-275
  53. ↑ Breward, L. and Gentle, M.J., (1985). Neuroma formation and abnormal afferent nerve discharges after partial break amputation (beak trimming) in poultry. Experientia, 41: 1132-1134. doi:10.1007/BF01951693
  54. ↑ Devor, M. and Rappaport, Z.H., (1990). Pain Syndromes in Neurology., edited by H.L. Fields, Butterworths, London, p. 47.
  55. ↑ Lunam, C.A., Glatz, P.C. and Hsu, Y-J., (1996). The absence of neuromas in beaks of adult hens after conservative trimming at hatch. Australian Veterinary Journal, 74: 46-49
  56. ↑ Kuenzel, W.J. (2001). Neurobiological basis of sensory perception: welfare implications of beak trimming. Poultry Science, 86: 1273-1282
  57. ↑ Lambton, S.L., Knowles, T.G., Yorke, C. and Nicol, C.J., (2010). The risk factors affecting the development of gentle and severe feather pecking in loose housed laying hens. Applied Animal Behaviour Science, 123: 32–42
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.