Introduction
The beak of a bird is not merely a keratinous structure, but is densely vascularised, enervated and serves several functions (Wild Reference Wild2015; Speer & Powers Reference Speer and Powers2016). Beaks possess mechano-, temperature-, pain- and even magnetic receptors (Gentle & Breward Reference Gentle and Breward1986). Birds use their beak for food and water uptake, and to maintain the plumage, e.g. removal of parasites, to align feathers, or distribution of preen oil (Clayton et al. Reference Clayton, Moyer, Bush, Jones, Gardiner, Rhodes and Goller2005; Zhao et al. Reference Zhao, Zhang, Zhao, Zhang and Godefroit2020). Pecking at objects, which are potentially edible, is a large component of the exploratory behaviour of birds. Pecking at conspecifics is part of the social behavioural repertoire, which may be affiliative (e.g. allopreening, gentle feather pecking), or defensive/aggressive (Leonard et al. Reference Leonard, Horn and Fairfull1995). Severe feather pecking (SFP), as can be observed in several poultry species kept in (intensive) commercial husbandry, is an injurious behaviour defined as the pecking at and pulling of feathers of conspecifics often leading to skin injuries and even cannibalism. Notably, aggressive pecking tends to be directed at the head area, while SFP is directed at the whole body (Bilcik & Keeling Reference Bilcik and Keeling1999). Severe feather pecking is thus not considered as a form of aggressive behaviour (Rodenburg et al. Reference Rodenburg, Van Krimpen, De Jong, De Haas, Kops, Riedstra, Nordquist, Wagenaar, Bestman and Nicol2013; van Staaveren & Harlander Reference Van Staaveren, Harlander and Nicol2020). Auto-pecking, or self-mutilation, is also observed in some avian species, predominantly in parrots and related species kept in captivity (Van Zeeland et al. Reference Van Zeeland, Spruit, Rodenburg, Riedstra, Van Hierden, Buitenhuis, Korte and Lumeij2009).
The causes of SFP remain, to date, largely elusive. Several potentially causal factors have been investigated, but the solution to prevent the emergence of the behaviour itself remains to be determined (e.g. Rodenburg et al. Reference Rodenburg, Van Krimpen, De Jong, De Haas, Kops, Riedstra, Nordquist, Wagenaar, Bestman and Nicol2013; Hartcher et al. Reference Hartcher, Wilkinson, Hemsworth and Cronin2016; Cronin & Glatz Reference Cronin and Glatz2020). Clearly, SFP is determined by a complex interplay of environmental (e.g. husbandry) and genetic (e.g. certain breed characteristics) conditions (Van Der Eijk et al. Reference Van Der Eijk, Lammers, Kjaer and Rodenburg2019; Kliphuis et al. Reference Kliphuis, Manet, Goerlich, Nordquist, Vernooij, Van Der Brand, Tuyttens and Rodenburg2023). The occurrence of SFP may be an indicator of the animals’ state of welfare. We define welfare as the individual being provided with the resources to reach a state that it perceives as positive (Arndt et al. Reference Arndt, Goerlich and Van Der Staay2022). These resources comprise external (e.g. husbandry and interventions), as well as internal (genotype and phenotype) characteristics. If an individual cannot adapt to the environmental circumstances, due to extrinsic or intrinsic factors, maladaptive behaviour may emerge (Arndt et al. Reference Arndt, Goerlich and Van Der Staay2022). Therefore, action is needed to ensure that husbandry methods and genetic selection enable individual animals to meet their mental and physical demands and reach a state they perceive as positive.
Despite the intensive research, SFP remains a worldwide challenge facing the poultry industry. The behaviour does not only occur in chickens (Gallus domesticus), but also in other species kept for commercial purposes, such as turkeys (Meleagris gallopavo domesticus), ducks (Cairina moschata; Anas platyrhynchos) and quail (Coturnix coturnix). A common management strategy to minimise the damage caused by SFP is beak trimming (also known as beak treatment, or beak tipping), which is the permanent removal of the tips of both upper and (usually) lower mandibles of a bird’s beak. Though initially introduced to improve poultry welfare, beak trimming is an invasive procedure that is criticised by scientists, animal welfare advocates and the public (Nordquist et al. Reference Nordquist, van der Staay, van Eerdenburg, Velkers, Fijn and Arndt2017). The procedure is considered to be painful, at least in the short term and potentially has long-term effects on behaviour, physiology, and morphology. Although beak trimming is shown to be effective in the reduction of feather damage caused by SFP in laying hens (van Staaveren et al. Reference Van Staaveren, Ellis, Baes and Harlander-Matauschek2021), it may cause both acute and chronic pain (Gentle Reference Gentle2011). This controversy has led to a ban on beak trimming in several European countries (Austria [Austrian Federal Government 2004], Norway [Norwegian Government Reference Government2009], the Netherlands [Government of The Netherlands 2013], and Sweden [Swedish Government 2018]). In the Netherlands, for example, exemptions are still made for parental chicken stocks, chicks that are destined for transport to countries where beak trimming is allowed, and turkeys. The underlying reasoning is that there are still no alternatives to prevent high rates of injury and mortality in untreated flocks (Ministerie van Landbouw, Natuur en Voedselkwaliteit Reference van Landbouw and en Voedselkwaliteit2023). Thus, billions of birds per year are still beak-trimmed worldwide. A common argument in favour of the removal of the sharp beak tips is the reduction of injuries and, consequently, mortality within a flock, as duller beaks cause less tissue damage if birds peck at the feathers and skin of their flock-mates (Nicol Reference Nicol and Mench2018). Beak trimming may alleviate the impact of SFP. It does not, however, solve the underlying problem – the damaging behaviour itself. Moreover, possible pain, tissue trauma, and nerve damage resulting from the beak-trimming procedure, and their consequences for behaviour and welfare need also to be considered. Over the past decades, the methods of beak trimming have been refined, e.g. moving away from the use of hot blades for cautery removal of the beak trip to less invasive techniques, such as infrared trimming (Glatz & Underwood Reference Glatz and Underwood2020). In the UK, for example, beak trimming is not banned but restricted to the use of infrared techniques only (Farm Animal Welfare Regulations 2010; Scottish Parliament 2010). Concerns regarding invasive interventions in the poultry industry, however, remain.
To inspire research on the causes and solutions to reduce injurious pecking (Fijn et al. Reference Fijn, van der Staay, Goerlich and Arndt2020) thereby disseminating findings to farmers and aid policy decisions, it is crucial to gather scientific evidence describing the (side) effects of beak trimming. A recent review investigated the effects of beak trimming, especially by hot blade, on production and welfare related traits in layer chickens (mortality, egg production and corticosterone; Gallina et al. Reference Gallina, Canozzi, Molinari, De Oliveira Júnior, Bianchi, Moreira, Olsson, Da Silva Pires, Sanchez and Peripolli2025). Results showed that beak trimming lead to elevated corticosterone (though the overall effect was not significant), tended to reduce mortality depending on the trimming depth, and did not affect egg production. However, the authors concluded that age at beak trimming, the method of trimming, and the study country were determinants of outcomes.
This systematic review took a broader approach to summarise evidence regarding the effects of beak trimming in several species of commercially kept poultry. As welfare is a complex concept, measures on behaviour, physiology, beak morphology and mortality were taken into account (Tiemann et al. Reference Tiemann, Fijn, Bagaria, Langen, Van Der Staay, Arndt, Leenaars and Goerlich2023). The research question, according to PICO format (Eriksen & Frandsen Reference Eriksen and Frandsen2018), was as follows: In commercially housed poultry (Population), what are the effects of beak trimming (Intervention) compared to no beak trimming (Control) on behaviour, physiology, beak morphology and mortality (Outcome)? Outcome parameters to study the effect of beak trimming compared to non-beak-trimmed controls were identified following an expansive search of the literature. The parameters were grouped and the effects of beak trimming on the direction of each outcome are reported.
Materials and methods
This review was conducted according to a protocol pre-registered on OSF on 14 February 2022 (https://osf.io/fnakr/). No amendments to the protocol were made. The review is reported according to the PRISMA guidelines (Page et al. Reference Page, McKenzie, Bossuyt, Boutron, Hoffmann, Mulrow, Shamseer, Tetzlaff, Akl, Brennan, Chou, Glanville, Grimshaw, Hróbjartsson, Lalu, Li, Loder, Mayo-Wilson, McDonald, McGuinness, Stewart, Thomas, Tricco, Welch, Whiting and Moher2021).
Study identification and screening
We comprehensively searched PubMed, CABdirect and Web of Science for studies presenting unique data on welfare effects of beak trimming in commercially kept birds. All databases were searched from inception until 23 January 2023, plus an updated search, using the same search strings, was performed on 26 January 2026 in PubMed and Web of Science. The full search strings are presented in Table 1. The records were imported into Endnote (Clarivate Analytics, Philadelphia, PA, version 21.2) to remove duplicates and then imported into the online screening platform Rayyan (Ouzzani et al. Reference Ouzzani, Hammady, Fedorowicz and Elmagarmid2016). Records were included if they were original, full-length articles published in English, German or translatable using online translation tools, describing controlled studies on beak trimming of avian species used in agriculture, to study commercial practice. The first screening phase was based on the records’ title and abstract. Potentially relevant records were subsequently screened for final inclusion based on their full texts. Each record was screened by two independent reviewers, and discrepancies were resolved through discussion, or by involving a third reviewer as arbiter. In both screening phases, exclusion criteria were non-avian species, ecological studies, non-agricultural bird populations, not explicitly studying beak-trimming-related interventions, no suitable control, unavailability of full-text, non-peer reviewed papers, conference abstracts, and reviews. No automation tools were used in the screening process.
Full search string for each database, to identify studies that report the effects of beak trimming on commercially kept poultry. The searches were executed on 23 January 2023 and 26 January 2026
Table 1. Long description
The table consists of two columns and three rows.
Row 1: Pubmed. The search string uses M e S H Terms and Title/Abstract tags. It combines three groups with A N D logic. Group 1: beak or beaks or bill or bills. Group 2: trimm asterisk or amputat asterisk or remov asterisk or mutilat asterisk or cut or cutting or blunt asterisk or debeak asterisk or beak conditioning or beak treat asterisk or tipp asterisk. Group 3: birds or avian or avians or bird or chicken or chickens or chick or chicks or gallus or hen or hens or broiler or broilers or pullet or pullets or cockerel or rooster or cockerels or roosters or duck super 1 or ducks super 1 or mulard or moulard or mulards or moulards or drake or drakes or goose or geese or turkey or turkeys or quail or quails or poultry or poultries or fowl or fowls or pheasant or pheasants or partridge or partridges or grouse or grouses.
Row 2: CABdirect. The search string follows the same three-group logic as Pubmed but without the database-specific tags like M e S H or T i a b.
Row 3: Web of Science. The search string is applied to all fields and follows the same keyword structure and grouping as CABdirect.
1 Note that the terms ‘Pekin’ and ‘Muscovy’ were omitted from the search string, as inclusion led to fewer results. Nevertheless, studies on both breeds were retrieved and are represented in our dataset.
Extraction of study characteristics
Data were extracted manually and gathered into Microsoft Excel® (Office 365, Microsoft Corporation®, Redmond, WA, USA). We extracted bibliographic details (e.g. authors, title), population and intervention details, such as species, strain, production system, beak trim variant), and an inventory of all outcome measures with a clear relevance to beak morphology, physical health, pain, physiology, mortality and/or behaviour.
Assessment of reporting of key quality indicators and risk of bias (RoB)
For all included studies, the reporting of several key quality indicators was assessed using the automated tool developed by Wang et al. (Reference Wang, Liao, Lapata and Macleod2022). The tool identifies reporting of blinding, randomisation, exclusion of animal/data/outcomes, compliance with animal welfare regulations and conflicts of interest. Previous systematic reviews of animal studies have consistently shown that poor reporting of these key quality indicators results in an unclear risk of bias across most domains, in both the individual studies and the body of evidence (see e.g. Prado-Rivera et al. Reference Prado-Rivera, Deddens, Fortuin, Wever and Olivier2025). Therefore, a full Risk of Bias (RoB) assessment using SYRCLE’s 142 RoB tool (Hooijmans et al. Reference Hooijmans, Rovers, De Vries, Leenaars, Ritskes-Hoitinga and Langendam2014) was performed for a random sample of 39 studies (25%), which was deemed sufficient to reliably capture the risk of bias profile of this evidence base. Each study was assessed by two reviewers and discrepancies were resolved through discussion. Results were visualised using ROBVIS (McGuinness & Higgins Reference McGuinness and Higgins2021).
Outcome data extraction and descriptive synthesis
Due to the wide variety in reported outcome parameters, we decided on a sub-set of variables relevant for poultry welfare to assess the effects of beak trimming. We distinguished between beneficial and harmful outcomes, i.e. an increase in the outcome respectively increases or decreases an individual’s welfare. The selected beneficial outcomes were preening, environmental pecking, and gentle pecking. The selected harmful outcomes were mortality, beak abnormalities, beak- and head-related behaviours indicative of discomfort, injurious pecking, wounds and injuries, physiological stress indicators and fearfulness (for a detailed overview of included terms per outcome, see Table 2). In each record, the context of the measured traits was checked, e.g. whether pecking was either directed to the environment or to other birds. Furthermore, the valence of the change in outcome was considered in terms of beneficial or harmful impact on welfare, e.g. the term ‘viability’ referred to mortality, but the valence of these outcomes is opposite. Due to a large variation of the included studies in terms of (i.e.) sample size, methods used, commercial or experimental setting, a meta-analysis was deemed unfeasible. Therefore, the data were synthesised using vote-counting (Borenstein Reference Borenstein2013), based on the direction of effect and visualised in an effect direction (ED) plot, which is a standardised alternative method to synthesise data in systematic reviews (Thomson & Thomas Reference Thomson and Thomas2013; Boon & Thomson Reference Boon and Thomson2021).
The outcome parameters and their descriptions that were used to identify relevant publications within the characteristics table, to select for further analysis in this systematic review on the effects of beak trimming on commercially kept poultry. The context in which these terms were used, e.g. pecking at other birds or pecking at the environment, and their valence in relation to welfare were always checked in the records, e.g. the opposite terms ‘mortality’ and ‘viability’
Table 2. Long description
The table consists of three columns: Outcome parameter related to welfare, Description, and Included terms.
* Preening: Manipulating own plumage with beak. Included terms: Preen.
* Environmental pecking: Exploring the non-food related environment with beak. Included terms: Pecking rate, pecking success, floor pecking, number of pecks, object peck, other peck, environment peck, exploratory peck, ground peck, litter-directed peck, rope peck.
* Gentle pecking: Making gentle beak contact with the body of another bird. Included terms: Gentle feather peck, gentle pecking, non-aggressive pecking, number of pullets preening penmates’ feathers, receiving gentle pecks.
* Mortality: Occurrence of death in the flock, independent of cause. Included terms: Mortality, culling, viability.
* Beak: Abnormal beak shape or histology. Included terms: Beak lesions, histology, nerve fibres, scarring, neuromas, swellings, beak sloughing, beak healing.
* Beak-head behaviour: Movements of head and/or beak, indicating potential pain. Included terms: Head shake, head flick, head rub, head scratch, beak wipe, beak rub.
* Injurious pecking: Bird pecks vigorously at feathers or skin of other birds, causing feather damage or wounds. Included terms: Cannibalism, feather pecking, feather pulling, injurious pecking, severe peck, vigorous feather peck, pecks and pulls, toe peck.
* Wounds and injuries: Wounds caused by injurious pecking. Included terms: Wounds/scars.
* Physiological stress indicators: Measurements of corticosterone C O R T and ratios of heterophils and lymphocytes H / L. Included terms: C O R T, H / L ratio, heterophil, lymphocyte.
* Fearfulness: Indicators of a fear response measured in behaviour tests. Included terms: Novel object, open field, latency to initial step, avoidance distance test, escape, fear, manual restraint, human approach, tonic immobility, nervousness, stress, time to cross initial boundary, vocalize.
1 Four studies did not report statistics on mortality, only a descriptive analysis. All other outcome parameters reported a statistical analysis.
Results
Study identification
From the 1,887 records obtained from three databases, 429 were included after screening for eligibility based on title and abstract. Of note, full texts were not retrievable for an unusually large percentage of these records (231/423; 55%); neither by the authors nor by the Utrecht University librarians. After full-text screening, 175 studies were included in the review (Figure 1).
Overview of the number of reports (k) on the effects of beak trimming in commercially kept poultry, in every stage of the article selection process, using the PRISMA method (Page et al. Reference Page, McKenzie, Bossuyt, Boutron, Hoffmann, Mulrow, Shamseer, Tetzlaff, Akl, Brennan, Chou, Glanville, Grimshaw, Hróbjartsson, Lalu, Li, Loder, Mayo-Wilson, McDonald, McGuinness, Stewart, Thomas, Tricco, Welch, Whiting and Moher2021).
Figure 1 Long description
Figure 1 is a PRISMA flow chart depicting the identification of studies via databases and registers, organized into four stages: Identification, Screening, and Included. Identification: Records were identified from databases between 23-01-2023 and 12-01-2026: k=308 (26 from PubMed), k=662 (172 from Web of Science), and k=719 (from CAB), totaling k=1,887. Before screening, records were removed: duplicate records removed (k=645) and records removed for other reasons (k=0). Screening: Records screened by title and abstract totaled k=1,242, of which k=812 were excluded. Reports sought for retrieval totaled k=430, of which k=231 were not retrieved. Reports assessed for eligibility by full text totaled k=199. Of these, reports were excluded for the following reasons: no suitable control (k=4), duplicate (k=12), and non-translatable or non-readable foreign language (k=8). Included: The final number of reports included in the characteristics table was k=175.
Study characteristics
The 175 included studies ranged from 1956 to 2025 (Supplementary File S1). Eight species were distinguished in the 175 included studies, with chickens being the most often investigated, followed by turkeys, quail, ducks, Guinea fowl (Numida meleagris) and pheasants (Phasanius cholchicus) (Figure 2a). The majority of studies involved animals kept for egg production (Figure 2b). The most used beak-trim method was hot blade (Figure 2c). Physical condition/physiology was the most often studied outcome category, and beak morphology was the least studied (Figure 2d).
Descriptive characteristics of studies that report effects of beak trimming on commercially kept poultry (k = 175), showing the number of studies (k) and proportion of total studies according to (a) species, (b) commercial purpose, (c) beak-trim variant and (d) reported outcome category.
Figure 2 Long description
Figure 2 presents four pie charts summarizing descriptive characteristics of the included studies. (a) Species: Chicken accounts for the large majority at 76% (n=133), followed by turkey at 12% (n=21), Japanese quail at 5% (n=9), Muscovy duck at 3% (n=6), and Guinea fowl, Pheasant, Pekin duck, and Bobtail quail each at 1% (n=2, 2, 1, and 1, respectively). (b) Commercial purpose: Eggs represent 64% (n=112), meat 21% (n=37), not reported 11% (n=19), and other 4% (n=7). (c) Beak trim variant: Hot blade is the most common method at 42% (n=73), followed by not reported at 22% (n=38), other at 11% (n=20), combination at 12% (n=21), infrared at 11% (n=19), and blunting/abrasion at 2% (n=4). (d) Outcome category: Physical condition/physiology is most frequent at 36% (n=133), followed by performance at 28% (n=106), behaviour at 22% (n=83), and beak morphology at 14% (n=51)
Most studies included only female birds (116; 66%), although sex was not reported in 19 studies (11%). Beak trimming was performed at the hatchery in 44 studies (25%), but more often the beak trim location was not reported (102; 58%). The average age of the first beak intervention was 1 day when performed at the hatchery, 101 days when performed elsewhere, and 33 days when the beak trim location was not reported. The mean number and range of animals per study is given in Table 3. In 14 studies, the number of animals was not reported. The most predominant housing systems were cage (82; 47%), followed by floor housing (56; 32%). The mean age at the end of data collection was 218 days (range: 1–658). An overview of the number of studies per species per beak trim variant is given for each outcome category in Table 4.
Mean number (N) and range of animals per study on effects of beak trimming per avian species, and the number of studies (k) in which N was not reported
Table 3. Long description
The table consists of four columns: Avian Species (with total studies k), Mean (N) per study, Range, and N not reported (k).
* Chicken (k = 133): Mean 5,401; Range 2 to 319,100; N not reported 13.
* Turkey (k = 21): Mean 760; Range 24 to 5,080; N not reported 0.
* Japanese Quail (k = 9): Mean 524; Range 180 to 816; N not reported 0.
* Muscovy duck (k = 5): Mean 193; Range 48 to 660; N not reported 1.
* Mulard duck (k = 1): Mean 0; Range 0; N not reported 1.
* Pheasant (k = 2): Mean 53; Range 45 to 60; N not reported 0.
* Guinea fowl (k = 2): Mean 1,000; Range 1,000 to 1,000; N not reported 0.
* Pekin duck (k = 1): Mean 192; Range 192; N not reported 0.
* Bobtail quail (k = 1): Mean 1,052; Range 1,052; N not reported 0.
* Grand Total (k = 175): Mean 4,508; Range 2 to 319,100; N not reported 15.
Number of studies (k) on the effects of beak trimming in commercially kept poultry, reporting outcome parameters from the selected categories, as shown per species and beak trim variant
Table 4. Long description
The table is organized into five columns: Species and beak trim variant, Beak morphology (k), Physical condition (k), Mortality (k), and Behaviour (k).
* Chicken (k = 133): Blunting/abrasion (2, 1, 2, 2); Combination (11, 16, 13, 11); Hot blade (11, 43, 35, 24); Infrared (7, 12, 8, 9); Not reported (4, 24, 20, 15); Other (1, 5, 2, 2).
* Turkey (k = 21): Combination (2, 2, 2, 0); Hot blade (0, 5, 3, 4); Infrared (3, 4, 3, 2); Not reported (0, 0, 0, 1); Other (1, 5, 2, 2).
* Japanese quail (k = 9): Blunting/abrasion (1, 1, 0, 0); Combination (1, 1, 1, 1); Hot blade (0, 5, 6, 2); Other (0, 1, 1, 0).
* Muscovy duck (k = 5): Not reported (0, 1, 1, 0); Other (3, 2, 1, 4).
* Pheasant (k = 2): Hot blade (0, 1, 0, 1).
* Guinea fowl (k = 2): Hot blade (0, 2, 2, 0).
* Pekin duck (k = 1): Combination (1, 1, 0, 1).
* Mulard duck (k = 1): Other (1, 0, 0, 0).
* Bobtail quail (k = 1): Other (1, 1, 1, 0).
The Grand Total (k = 175) across all categories is: Beak morphology 51, Physical condition 133, Mortality 106, and Behaviour 83.
1 The term “Combination” refers to the parallel investigation of several beak trim variants in one study, e.g. hot blade and infrared.
2 Other beak trim variants were reported, such as scissors in Muscovy ducks, a bio-beaker in turkeys and an electric debeaker in chickens and turkeys.
Additional interventions that were studied in the included literature were sex, genotype, group composition, stocking density, environmental enrichment, type of drinker, feather colour, light intensity, husbandry system, analgesics, infestation with mites and lice, treatment of plumage with bitter almond oil, age of beak trimming, diet, dewinging, blunting devices, foster mother, vaccination, season, and clip-on spectacles.
The number of studies per beak trim variant per decennium shows that hot blade trimming was the most often studied method until 2010, after which infrared trimming became more prevalent (Figure 3).
Stacked bar graph showing the number of studies (k) on the effects of beak trimming in commercially kept poultry, per beak trim variant per decennium of publication (e.g. 1950 reflecting 1950–1959). The category ‘combination’ refers to studies comparing multiple beak-trim variants to a control group.
Figure 3 Long description
Figure 3 is a stacked bar chart showing the number of studies (k) using each beak trim variant by decade, 1950–2020: Not reported, Other, Hot blade, Combination, Blunting/abrasion, Infrared. 1950: k=1 (Not reported 1). 1960: k=1 (Hot blade 1). 1970: k=11 (Not reported 3, Other 3, Hot blade 5). 1980: k=21 (Not reported 7, Other 2, Hot blade 12). 1990: k=46 (Not reported 7, Other 7, Hot blade 29, Combination 3). 2000: k=30 (Not reported 9, Other 1, Hot blade 11, Combination 7, Blunting/abrasion 1, Infrared 1). 2010: k=44 (Not reported 8, Other 4, Hot blade 14, Combination 7, Blunting/abrasion 2, Infrared 9). 2020: k=21 (Not reported 3, Other 3, Hot blade 1, Combination 4, Blunting/abrasion 1, Infrared 9). Study numbers rose sharply to a 1990s peak, in which hot blade trimming was the dominant method. This method stayed dominant through the 2000s–2010s. Combination and infrared methods emerged from the 2000s, with infrared becoming prominent by the 2010s–2020s as hot blade use declined.
Reporting of key quality indicators and risks of bias (RoB)
The reporting of key quality indicators by the included studies is shown in Figure 4 (full traffic light plot in Supplementary File S2), and the RoB assessment based on 39 records is summarised in Figure 5 (full RoB assessment as Excel® file in Supplementary File S3). In general, the included articles had a high RoB. This was mainly due to experimenters not being able to be blinded for the beak treatment for most studies. Furthermore, although 50% of the studies reported that animals were randomly assigned to the treatment groups, only three studies described the actual method of how this assignment took place.
Summary of reporting of several key quality indicators in the records reviewed (k = 175), on the effects of beak trimming in commercially kept poultry.
Figure 4 Long description
The five study quality indicators are each split into three categories with different colours in the stacked bar chart: Reported (green), Not Reported (red), and Could not be assessed (blue), as percentages of studies. Blinded assessment of outcome(s) reported? 16% Reported, 70% Not Reported, 14% Could not be assessed. Random allocation to experimental groups reported? 53% Reported, 37% Not Reported, 10% Could not be assessed. Statement on animal, data or outcome exclusions reported? 18% Reported, 68% Not Reported, 14% Could not be assessed. Compliance with animal welfare regulations reported? 25% Reported, 61% Not Reported, 14% Could not be assessed. Conflict of interest statement reported? 27% Reported, 59% Not Reported, 14% Could not be assessed. Overall, random allocation was the most commonly reported indicator, while blinded outcome assessment was the least commonly reported, with the other three indicators reported by roughly a quarter of studies each.
Summary of the full RoB assessment in the subset of studies (k = 39), on the effects of beak trimming in commercially kept poultry. The stacked bar graph shows the number of times the reviewers answered Yes (low RoB), Unknown (unknown RoB) or No (high RoB) to each of the ten questions from SYRCLE’s tool for assessing RoB (Hooijmans et al. Reference Hooijmans, Rovers, De Vries, Leenaars, Ritskes-Hoitinga and Langendam2014). Each record was reviewed by two reviewers, and both assessments were cumulatively added to the graph.
Figure 5 Long description
Allocation sequence adequately generated/applied: Yes 1, Unknown 71, No 1. Groups similar at baseline/adjusted for confounders: Unknown 22, No 51. Allocation adequately concealed: Unknown 45, No 28. Animals adequately randomly housed: Yes 7, Unknown 63, No 3. Caregivers/investigators adequately blinded: Unknown 24, No 49. Animals adequately randomly selected at outcome assessment: Yes 4, Unknown 67, No 2. Outcome assessment adequately blinded: Unknown 22, No 51. Incomplete outcome data adequately addressed: Yes 6, Unknown 64, No 3. Study free of selective outcome reporting: Yes 41, Unknown 30, No 2. Study apparently free of other bias risks: Yes 18, Unknown 52, No 3. Overall, “Unknown” dominates most items, reflecting poor reporting of methodological detail, while selective outcome reporting (item 9) was the most frequently rated “Yes,” and baseline similarity and blinding items (2, 5, 7) show the highest “No” (high risk) ratings.
Effect-direction plots (k = 120) showing the effects of beak trimming on the welfare of (a) chickens and (b) other species, as indicated by the selected outcome parameters, and (c) a separate plot illustrating the effects of beak trimming on mortality in all poultry species. Green headers show beneficial welfare indicators and red headers show harmful welfare indicators. The direction of the arrows depicts either an increase, decrease or no change in the beak-trimmed birds compared to non-beak-trimmed controls. The colour of the arrows indicates the valence of the effect in relation to welfare (red is a harmful impact, green is beneficial). Asterisks indicate an interaction between beak-trim variant and another factor (e.g. breed or type of husbandry).
Figure 6a Long description
Figure 6a is an effect direction plot with 49 chicken studies as rows (author and year) and 9 outcome columns: Preening, Environmental pecking, Gentle pecking, Beak abnormalities, Beak-head behaviour, Injurious pecking, Wounds & injuries, Physiological stress indicators, and Fearfulness.Each cell contains a symbol indicating the study’s finding for that outcome: a green upward triangle = increase, a red downward triangle = decrease, a grey double-headed arrow = no significant difference, and an asterisk denotes an additional note (e.g., Hartcher et al. 2013 and Vezzoli et al. 2015 show marked findings). Most cells are blank, indicating that outcome was not measured in that study.Overall, injurious pecking and fearfulness show a mix of increases, decreases, and no differences across studies, while beak abnormalities are more frequently reported as increased. Due to the plot’s size, individual cell values are not listed here; the main text should be consulted for full detail.
Figure 6b Long description
Figure 6b is an effect direction plot with 21 studies as rows (author, year, and species: Japanese quail, Muscovy duck, Pekin duck, Pheasant, Turkey) and 9 outcome columns: Preening, Environmental pecking, Gentle pecking, Beak abnormalities, Beak-head behaviour, Injurious pecking, Wounds & injuries, Physiological stress indicators, and Fearfulness. Each cell contains a symbol for the study’s finding: a green upward triangle = increase, a red downward triangle = decrease, a grey double-headed arrow = no significant difference. Most cells are blank, meaning that outcome was not measured. Overall, beak abnormalities are frequently reported as increased (e.g., in Muscovy duck and turkey studies), while injurious pecking and wounds/injuries show mixed increases, decreases, and no differences, particularly in studies on turkeys. Physiological stress indicators show both increases and decreases across species. The main text should be consulted for full details.
Figure 6c Long description
Figure 6c is an effect direction plot listing 49 studies (author, year, species) with a single “Mortality” outcome column. Species include Bobtail quail, Chicken (the majority), Guinea fowl, Japanese quail, Muscovy duck, and Turkey. Symbols indicate findings: green downward triangle = decreased mortality, red upward triangle = increased mortality, grey double-headed arrow = no significant difference. Across the 49 studies: 24 report decreased mortality (mostly chickens, plus bobtail quail, Japanese quail, and turkey studies), 21 report no significant difference (chickens, Japanese quail, Muscovy duck, and turkey studies), and 4 report increased mortality (Ben-Mabrouk 2023, McDonald 1956, Pescatore 1988 in chickens; Laganá 2011 in Japanese quail). Overall, decreased mortality is the most commonly reported finding, followed by no difference, with increased mortality reported least often. The main text should be consulted for full detail.
Effect of beak trimming on welfare indicators
Among the 175 studies included according to the inclusion criteria, 120 reported one or more outcome parameters selected for further analyses based on domains of welfare, namely behaviour, morphology, physiology, and mortality (Table 2). The results extracted from these 120 studies are depicted in ED plots (Figure 6a–c).
Beak abnormalities
Out of 24 studies investigating abnormalities in beak histology or sensory traits (15 in chickens, 9 in other species), 17 (71%) reported deviations in beak-trimmed birds compared to control, and 7 studies (29%) reported no beak abnormalities (Figures 6a and b).
Physiology
Physiological stress indicators (CORT and/or L/H ratio) were investigated in 14 studies (8 in chickens, 6 in other species). Respectively, these studies reported a decrease (4; 29%), no effect (6; 42%) or an increase (4; 29%) in stress indicators in beak-trimmed birds compared to the control (Figures 6a and b).
Behaviour
Preening was investigated in 22 studies (17 in chickens, 5 in other species). Of these, 8 (36%) reported a decrease, 10 (46%) reported no effect, and 4 (18%) reported an increase in preening in beak-trimmed birds compared to the control. Environmental pecking was investigated in 24 studies (17 in chickens, 7 in other species). Respectively, 16 studies reported a decrease (67%), 7 no effect (29%), and 1 study reported an increase (4%) in environmental pecking observed in beak-trimmed birds compared to control birds. Gentle pecking was reported in 12 studies (11 in chickens, 1 in turkeys), of which 4 (33%) showed an increase, 5 (42%) showed no effect, and 3 (25%) showed a decrease in this behaviour for beak-trimmed birds. Eight studies (5 in chickens, 3 in other species) investigated beak and head-related behaviours that may be indicative of pain. Of these, 4 (50%) reported a decrease, 3 (38%) reported no effect and 1 (12%) reported an increase of these behaviours. Injurious pecking was reported in 17 studies (11 in chickens, 6 in other species). Of these, 5 (29%) reported a decrease, 9 (53%) reported no effect and 3 (18%) reported an increase in injurious pecking. Eleven studies investigated wounds and injuries caused by pecking (4 in chickens, 7 in other species). Of these, 8 (73%) reported a decrease, and 3 (27%) reported no effects of beak trimming on wounds and injuries. Fear-related behaviours were investigated in 12 studies (10 in chickens, 2 in other species), mostly during standardised fear tests, such as the open field test or tonic immobility test. Of these, 3 (25%) reported an increase, 6 (50%) reported no effect and 3 (25%) reported a decrease in fear-related behaviours in the beak-trimmed birds compared to control (Figure 6a and b).
Mortality
Out of 49 studies investigating mortality caused by pecking injuries, 25 (51%) showed a decrease, 20 (41%) showed no effect, and 4 (8%) showed an increase in mortality in the beak-trimmed birds compared to the control (Figure 6c).
Discussion
The aim of this systematic review was to provide a thorough overview of available evidence on the effects of beak trimming on behaviour, physiology, morphology and mortality of commercially used poultry species. We chose these domains to focus on more than just mortality and production traits, and rather relate the findings to animal welfare, which comprises both physical and mental well-being (Arndt et al. Reference Arndt, Goerlich and Van Der Staay2022).
Effect of beak trimming on welfare indicators
To assess welfare, we recommend the combination of observations, focusing both on external and animal-based welfare indicators. The latter can be divided into domains, such as behaviour (as a proxy for the mental state), morphology (health, physical injuries) and physiology (mortality, indicators of the physiological response to stressors; Tiemann et al. Reference Tiemann, Fijn, Bagaria, Langen, Van Der Staay, Arndt, Leenaars and Goerlich2023). For our descriptive synthesis, we therefore selected studies that reported on one or more outcome parameters that we categorised as either beneficial or harmful to animal welfare, according to our definition (Arndt et al. Reference Arndt, Goerlich and Van Der Staay2022), resulting in a subset of 120 out of the original 175 included records. The goal was to include a multitude of variables to reflect the complex concept of welfare, which goes beyond production and mortality. SFP has multiple causes and consequences, which ideally should be evaluated on an individual level, as population means may not be sufficiently informative to identify causes. Animal personality, thus individual differences, have been acknowledged as modifying factors in farm animals (Finkemeier et al. Reference Finkemeier, Langbein and Puppe2018), and in the case of injurious pecking, the aetiology may differ for perpetrators and victims. Interestingly, while FP clearly has a genetic component (Iffland et al. Reference Iffland, Wellmann, Schmid, Preuß, Tetens, Bessei and Bennewitz2020), the individual consistency of being a feather pecker or a victim was shown to be low in laying hens (Daigle et al. Reference Daigle, Rodenburg, Bolhuis, Swanson and Siegford2015).
Surprisingly, beak morphology was one of the understudied aspects within the context of identifying consequences of beak trimming. Yet, within the literature some suggest that – often permanent, e.g. as reported by Schwean-Lardner et al. (Reference Schwean-Lardner, Annett-Christianson, Rajendram and Classen2016) – beak abnormalities can be caused by beak trimming. However, the method and severity of trimming should be taken into account, as infrared trimming has been suggested to induce less-negative results compared to hot blade (Glatz & Underwood Reference Glatz and Underwood2020). Most abnormalities related to altered nerve fibres in the beak tip. As described in the Introduction, the beak represents a sensitive morphological feature in avian species, which emphasises the, possibly underestimated, impact of a mutilation. In combination with the altered head- and beak-related behaviours to avoid painful stimuli (Gentle Reference Gentle2011), these findings may indicate both acute and prolonged pain in beak-trimmed poultry. Moreover, the animals may be limited in the expression of their normal behavioural repertoire, though the studies included in this review did not show a clear direction of effect. The three studies that investigated the effects of beak trimming on ectoparasite load, all reported a higher abundance of lice and/or mites in beak-trimmed laying hens (Mullens et al. Reference Mullens, Chen and Owen2010; Chen et al. Reference Chen, Haith and Mullens2011; Vezzoli et al. Reference Vezzoli, Mullens and Mench2015). While the performance of the (preening) behaviour itself might not be affected by beak trimming (e.g. Sandilands & Savory Reference Sandilands and Savory2002), an intact beak is likely important for the removal of ectoparasite infestations.
Relatively few studies considered physiological traits while studying the effects of beak trimming. The majority of studies investigating physiological indicators of stress reported no effect of beak trimming on corticosterone or the heterophil: lymphocyte ratio, though a related meta-analysis cautiously suggests an increase in corticosterone in layer hens beak-trimmed with a hot blade (Gallina et al. Reference Gallina, Canozzi, Molinari, De Oliveira Júnior, Bianchi, Moreira, Olsson, Da Silva Pires, Sanchez and Peripolli2025). Although the role of glucocorticoids as an indicator of compromised welfare is complex, changes in concentrations can be informative indicating an acute physiological stress response or even chronic changes (Tiemann et al. Reference Tiemann, Fijn, Bagaria, Langen, Van Der Staay, Arndt, Leenaars and Goerlich2023). While we did not analyse the details of the included studies on the method and timing of, e.g. corticosterone measurements in relation to the beak trimming event, this aspect is crucial for the interpretation and may have added to the variation in our results. Beak trimming may induce an acute stress response due to the handling, restriction and potential acute pain. In the usual hatchery processing, however, beak trimming is only one stressor that chicks are exposed to; multiple transport moments, sorting and sexing, vaccination, conveyer belts, and handling all pose challenges to the adaptive capacity of young animals with potential long-term consequences (Adcock Reference Adcock2021). The procedures at commercial hatcheries have previously been linked to SFP and diminished welfare in layer chickens (Hedlund & Jensen Reference Hedlund and Jensen2021, Reference Hedlund and Jensen2022).
Mortality decreased in beak-trimmed birds compared to controls in more than half of the studies, however, a comparable number of studies reported no effects of beak trimming on mortality and several even showed an increase in deaths and culls. The studies reporting a lack of effect on mortality covered mostly chickens, but also Guinea fowl, quail, ducks and turkeys. These results indicate beak trimming not to be universally reducing mortality rates thereby weakening the main argument in favour of such intervention. Mortality, however, is often universally reported, more details on the causes of death, e.g. directly related to the trimming procedure or due to other factors, would aid the interpretation of this outcome. Nevertheless, alternative solutions for the mitigation of causes of mortality due to SFP urgently need to be found.
Preening, environmental pecking and gentle pecking were selected as indicators of a positive state of welfare, relating to comfort behaviour, exploration and social interaction. Of these variables, environmental pecking seemed to be most prominently affected by beak trimming. Exploring the environment is an important biological function of the beak. Studies that reported a decrease in exploration behaviour in the beak-trimmed group address the lack of clarity as to whether the reduction in this behaviour is caused by chronic pain, or by the systematic experience of functional losses during beak use (Van Liere Reference Van Liere1995; Hartcher et al. Reference Hartcher, Tran, Wilkinson, Hemsworth and Cronin2013). Only a small number of studies specifically investigated pain-related behaviours, such paucity perhaps due to the applied selection criteria. A recent review on the recognition and assessment of pain in avian species reported similar changes in behaviour following beak trimming in chickens and turkeys, as well (Mikoni et al. Reference Mikoni, Guzman, Fausak and Paul-Murphy2022). Options to minimise pain through analgesia seem limited (Alfirevich et al. Reference Alfirevich, Keshavarzi, Sandilands and Small2025), while the refinement of beak trimming method (e.g. infrared at an early age) seems to have led to improvements (Guatteo et al. Reference Guatteo, Levionnois, Fournier, Guémené, Latouche, Leterrier, Mormède, Prunier, Servière, Terlouw and Le Neindre2012). The method of beak trimming was not used as a predictor of study outcomes in the ED plots due to the large variation in outcome parameters, resulting in a small number of studies per parameter. A recent review investigating the differences between hot blade and infrared trimming in the Australian layer industry concluded that infrared beak trimming seems to be a less painful procedure than hot blade trimming, although the occurrence of adverse effects of the trimming procedure is highly dependent upon the severity of trimming (Glatz & Underwood Reference Glatz and Underwood2020). Our results indicate that studies on beak trimming using the hot blade technique are becoming less prevalent, supporting the trend towards infrared as a less invasive method. Of course, the reality observed in practice may not reflect these recent research trends. A further investigation of the relationship between the application of different techniques, the beak-trim variant and the severity of welfare consequences, is surely warranted (Gallina et al. Reference Gallina, Canozzi, Molinari, De Oliveira Júnior, Bianchi, Moreira, Olsson, Da Silva Pires, Sanchez and Peripolli2025). More insight into this relationship would aid policy-makers to regulate the refining of methods to minimise pain and negative consequences of beak trimming. In addition, mitigating the pain of beak trimming through analgesia should be considered as routine treatment (Guatteo et al. Reference Guatteo, Levionnois, Fournier, Guémené, Latouche, Leterrier, Mormède, Prunier, Servière, Terlouw and Le Neindre2012).
The large number of studies in which behavioural changes were observed due to the trimming procedure, either in preening, environmental pecking, gentle pecking, and beak-head-related behaviours, indicate that beak trimming causes both short- and long-term behavioural changes in poultry. In total, 17 of 175 studies investigated the occurrence of injurious pecking. The body of research suggests that beak trimming mostly alleviates the symptoms of injurious pecking, but the underlying causes persist, and therefore animal welfare is still threatened, taking coping and adaptation into account (Arndt et al. Reference Arndt, Goerlich and Van Der Staay2022). While causal factors that have been identified lead to a multifactorial situation (Rodenburg et al. Reference Rodenburg, Van Krimpen, De Jong, De Haas, Kops, Riedstra, Nordquist, Wagenaar, Bestman and Nicol2013; van Staaveren & Harlander 2020), the development of SFP is still not well understood, and calls for further investigation. In light of recent developments geared towards sustainable and welfare-oriented animal agriculture, more efforts need to be made to meet the needs of the animals to prevent injurious behaviours. Further, preserving the animals’ physical appearance is key in enabling support of the expression of their biological needs. The provisioning of environmental enrichment as well as selection during breeding has the potential to drastically reduce SFP and feather damage but needs to be combined with other management strategies in order to be successful (van Staaveren et al. Reference Van Staaveren, Ellis, Baes and Harlander-Matauschek2021).
Study characteristics
During data extraction, it was noted that reporting of experimental details could be improved, e.g. the location of beak trimming, the method of beak trimming (e.g. hot blade or infrared), or the age at which the procedure took place were not consistently reported. This lack of information impedes comparison of studies and their outcome. Plausibly, general assumptions made on common practices explain this lack of reporting.
As we did not restrict our literature search to a certain timeframe, included studies were performed from 1956 up to 2025. Historical developments surely are of importance when synthesising welfare-related outcomes, as beak trimming techniques, husbandry, and breeds have evolved considerably during this timeframe. For example, in recent years, infrared trimming is gradually replacing hot blade trimming, as infrared techniques may lead to less negative impact on the bird (Glatz & Underwood Reference Glatz and Underwood2020).
Regarding the study populations, the number of animals per study varied widely, ranging from histological observations in two birds to studies involving 34 commercial flocks of more than 100,000 birds. This variation likely reflects the goal of investigating both fundamental aspects of beak trimming on the individual bird, as well as studying the impact of beak trimming under applied conditions. The inclusion of a high number of farms in applied research is positive, as differences in management and breed are shown to be factors in the emergence of SFP. These studies, however, are mostly correlative, and due to the large variation in husbandry, causal factors are difficult to identify. More experimental studies are needed, testing interventions to prevent the emergence of SFP in commercial husbandry, aligning with the trend to ban mutilations in farmed animals; aspects to be investigated are adapting the housing conditions to better match the birds’ behavioural needs, taking species-specific biology into account, investigating gene × environment effects, and the impact of stress-inducing procedures. While they continue to exist, procedures such as beak trimming require continuous refinement.
The study population also reveals that the majority of publications were focused on birds kept for egg production. As SFP usually emerges around age of maturation (Van Hierden et al. Reference Van Hierden, Korte, Ruesink, Van Reenen, Engel, Koolhaas and Blokhuis2002), it is rarely a problem in broiler chicks raised for meat production who never reach maturity. In the parental stocks (referred to as broiler breeders), however, SFP is an issue yet was only investigated by two studies. Chickens were the most represented study species, though SFP is also shown by other poultry species, such as turkeys, quail, ducks, Guinea fowl, and pheasants. The ubiquitous existence of injurious behaviour, despite diverging biological and ecological features of the different species, poses the question of a common conflict between the husbandry and biological needs of the respective species, an aspect that deserves further investigation.
Study limitations
While systematic review methodology provides a structured process to evidence synthesis, including several measures to reduce bias, our work has some limitations. Although we identified a large number of studies, the high variability in their characteristics and outcomes made a meta-analysis unfeasible. As a result, no numerical estimate of the magnitude of the effect and heterogeneity of the evidence can be given, and publication bias could not be assessed. Instead, we summarised the evidence based on the reported direction of effect and created ED plots for visualisation. This combination was deemed most suitable to assess whether there is any evidence of an effect, in the absence of consistent outcomes reported across studies. However, the results should be interpreted with care, as this methodology is under development and does not account for effect sizes (Thomson & Thomas Reference Thomson and Thomas2013; Boon & Thomson Reference Boon and Thomson2021). Due to the large variation between studies, several aspects remain to be investigated in more detail. The welfare consequences of beak trimming depend on the method used (e.g. infrared being an improvement compared to cautery methods), the severity of trimming (how much of the beak is actually removed), the age at which birds are trimmed (preventive after hatch or at a later age during a pecking outbreak), the age at which outcomes are measured (acute vs chronic), breed/hybrid, and husbandry conditions. Deeper exploration of the relationship between outcomes and age would be a valuable addition to this body of evidence, and we invite further analyses on our dataset (Supplementary File S1).
Application and alternatives
Injurious behaviour of animals in commercial husbandry is a widespread phenomenon. For example, in pigs, tail biting is a welfare problem and the discussion surrounding the docking of tails (i.e. the removal of the tail of piglets at a very young age; Nordquist et al. Reference Nordquist, van der Staay, van Eerdenburg, Velkers, Fijn and Arndt2017), shows parallels to the challenges regarding beak trimming in poultry. In both cases, the underlying causes leading to the emergence of injurious behaviour are complex and call for further research, as sustainable and non-invasive solutions are missing to date (Fijn et al. Reference Fijn, van der Staay, Goerlich and Arndt2020). Both the determinants for being a victim or a perpetrator need to be identified, as birds that perform SFP likely suffer from compromised welfare as well. Injurious pecking at conspecifics may be a coping strategy to deal with (unfulfilled) behavioural needs (Cronin & Glatz Reference Cronin and Glatz2020), early adversity (De Haas et al. Reference De Haas EN, Edgar, Riber, Estevez, Ferrante, Hernandez, Kjaer, Ozkan, Dimitrov, Rodenburg and Janczak2021), and/or the result of neurological or physiological imbalances (De Haas et al. Reference de Haas EN, Kjaer, Jensen and Guererro-Bosagna2024). The dilemma regarding mutilations of animals remains, balancing the welfare and integrity of the individual animal vs the health of the flock. With this review, we emphasise the importance of measurements on an individual level, such as beak deformations or changes in behaviour which might indicate diminished welfare due to beak trimming.
Alternative solutions to prevent pecking injuries and mortality are being investigated, though mostly in chickens. It is possible to genetically select against the behaviour itself, resulting in high and low FP lines (Kjaer Reference Kjaer2009), supporting the notion that SFP has a genetic component, and some breeds or hybrids may be more prone to developing this behaviour. However, selection on low occurrence of FP behaviour may negatively affect productive parameters, thus, to be adapted by the commercial industry, economic interests need to be come under consideration (e.g. Su et al. Reference Su, Kjaer and Sørensen2006). Moreover, given that SFP had a genetic predisposition in commercially bred laying hens, even the most optimal housing conditions may not prevent the behaviour from occurring.
Studies investigating behavioural and physiological traits in different FP lines indicate differences in fear-related behaviours and coping style (Van Der Eijk et al. Reference Van Der Eijk, Lammers, Li, Kjaer and Rodenburg2018), and in hormones related to stress physiology (Korte Reference Korte1997). As perinatal exposure to stressors in management and husbandry may influence the development of SFP, further research on early life adversities is needed (De Haas et al. Reference De Haas EN, Edgar, Riber, Estevez, Ferrante, Hernandez, Kjaer, Ozkan, Dimitrov, Rodenburg and Janczak2021). Hatchery processing has been shown to elicit a stress response with potential long-term effects in chickens (Hedlund et al. Reference Hedlund, Whittle and Jensen2019). Other poultry species, such as turkeys, might undergo several invasive procedures during early life, such as the removal of toenails or snoods, which are typically performed without analgesia, while likely inducing pain (Alfirevich et al. Reference Alfirevich, Keshavarzi, Sandilands and Small2025). To refine husbandry procedures, interventions, such as light during incubation or enrichment during the juvenile phase are being tested, in addition to nutrition (e.g. Kliphuis et al. Reference Kliphuis, Manet, Goerlich, Nordquist, Vernooij, Van Der Brand, Tuyttens and Rodenburg2023). The use of dark-brooders, large heating plates with curtains mimicking some aspects of maternal care, show promise in helping reduce the risk of SFP (e.g. Jensen et al. Reference Jensen, Palme and Forkman2006). Despite the robust positive effects, however, the translation into commercial practice is largely lacking (Sirovnik & Riber Reference Sirovnik and Riber2022).
The complex interplay between early life experiences, fearfulness, coping style and SFP needs to be studied in more detail before genetic selection can be applied on a large scale, to avoid other negative consequences for the welfare of the animals.
Next to behaviour, beak shapes that are less damaging can also be selected for. Recent research shows there is a natural variety in beak shapes among commercial laying hens, which has the potential to reduce pecking damage, given that changes in beak shape do not entail negative consequences for the behaviour and welfare of the bird (Struthers Reference Struthers2023). Long-term blunting of the beak by providing abrasive material, such as pumice, has been investigated as another alternative to trimming (Fiks-van Niekerk & Elson Reference Fiks-van Niekerk and Elson2005). This method has been shown to reduce feather damage in quails without any observed negative effects (Taskin & Camci Reference Taskin and Camci2017). However, the use of a blunting feeder was not effective in the reduction of cannibalism in laying hens (Struthers et al. Reference Struthers, Buchynski, Chew, Gomis, Herwig, Shynkaruk and Schwean-Lardner2022) or turkeys (Grün et al. Reference Grün, Damme, Müller, Sommer, Schmidt, Erhard and Bergmann2021). The effectiveness of the intervention appears to be linked to a variety of aspects, such as the attractiveness and the type of abrasive material. Important to note is that alternatives to beak trimming, which aim at changing the animals’ physical appearance, such as blunting and genetic selection on beak shape, continue to ignore the underlying causes of injurious pecking and are therefore merely alternative strategies for ‘damage control’.
Animal welfare implications
Despite beak-trimming methods having undergone refinement in recent years, the procedure not only leads to acute pain and stress but may also affect welfare in the long term, although detailed conclusions were difficult to draw from the heterogenous dataset. We defined welfare as the ability to cope and adapt to reach a state that the individual perceives as positive, and our results indicate that beak trimming has effects on both physical and behavioural parameters, with potential negative consequences for the mental state of the individual. Of major concern should be that severe feather pecking emerges in a wide range of poultry species kept under commercial conditions. Notably, the consequences of omitting beak trimming, in the current husbandry systems, needs urgent evaluation and suggestions for alternatives. To safeguard welfare of both the individual and the flock, more effort should be taken to understand the causes of SFP, and potential species differences.
Conclusion
This review provides an extensive overview on the effects of beak trimming on behaviour, physiology, beak abnormalities, and mortality of several commercially kept poultry species. Beak trimming seems to contribute to a reduction of risk of the consequences of SFP, although not universally, especially as welfare-supporting behaviours may also be impacted simultaneously. Given the large variation in the included studies, both in the methods and timing of beak trimming, and the assessment of outcome parameters, conclusions need to be drawn cautiously, even although the need to alleviate the impact of interventions such as beak trimming in the poultry sector, remains apparent. While refinement of techniques is taking place, e.g. omitting hot blade in favour of infrared trimming, identification of the complex interplay between causal factors of SFP (e.g. genetics, husbandry) is urgently needed. Several countries have banned this practice altogether, calling for an objective overview of the consequences of omitting beak trimming in terms of animal welfare, ethics, and economics. An important task for the scientific community is to further investigate the underlying causes of SFP, identify husbandry interventions that may lead to, or prevent SFP, and to suggest improvements for the welfare of the various poultry species kept for commercial purposes.
Supplementary material
The supplementary material for this article can be found at http://doi.org/10.1017/awf.2026.10113.
Acknowledgements
The authors would like to thank Shannon Douglas and Loes Markus for their help in the data extraction, Jary Weerheijm and colleagues at the Utrecht University library for their assistance in retrieving the literature, and Sean Smith for running the RoB reporting AI. Finally, we thank Victoria Sandilands, the anonymous reviewer, and the editorial board for their constructive comments on the manuscript.
Funding statement
This work was financially supported by the ZonMw program ‘More knowledge with fewer animals (MKMD, the Netherlands)’, project number 114024151. This work was financially supported by the ZonMw program ‘More knowledge with fewer animals (MKMD, the Netherlands)’, project number 114024151.
Competing interests
None.
Declaration of AI-assisted technologies in the writing process
The authors did not use AI tools during the preparation or revision of the manuscript. The authors independently verified the relevant literature, reviewed and edited all manuscript content, and take full responsibility for the final published article.
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