Feather Pecking and Cannibalism in Game Birds

ISSN 1313-3551 (online) doi:10.15547/tjs.2020.04.012

Review INFLUENCING FACTORS LEADING TO DAMAGING BEHAVIOR - FEATHER PECKING AND CANNIBALISM IN GAME BIRDS

S. Nikolov*, D. Kanakov

Department Internal Non-infectious Diseases, Faculty of Veterinary Medicine, Trakia University, Stara Zagora, Bulgaria

ABSTRACT Behavioural disorders, including feather pecking and cannibalism, are a common problem in both domestic and wild birds. Damaging behaviour is polyethiological and is divided into two major groups of factors: extrinsic and intrinsic. Extrinsic factors are those that are not dependent on the species of bird-factors from outside the organism which causes injurious pecking (IP). There are three abiotic groups assigned: nutritional factors (the composition of the ration and nutritional strategies), factors of the environment (light, temperature, sound, and air), and conditions of breeding (density, size, type of system, and enrichment of the conditions of breeding). Intrinsic are the factors that depend on the species of bird – factors coming from the organism and influencing injurious pecking. Seven biotic factors are assigned: social (imitating, sexual, stereotypical and maternal behaviour), sex (male and female sex hormones), age (young and adult), stress (fear, stress and corticosterone), central-nervous (serotonin, dopamine and noradrenaline), hereditary (genotypic and phenotypic manifestation) and immunological. It is important to have an understanding of the influencing factors leading to an onset of injurious pecking in order to successfully control the behavior in game birds bred in captivity.

Key words: damaging behavior, injurious pecking (IP); feather pecking (FP); cannibalism, pheasant, game birds

INTRODUCTION detailed classification of the influencing The main obstacle when breeding game birds factors leading to damaging behavior in game in captivity or a large number of domestic birds. The abiotic and biotic factors are birds in one area is the onset of injurious reviewed as well as the interaction between the pecking (IP) which leads to a decline in their environment and the organism, leading to welfare (1, 2). This results in serious economic stressful situations and dissatisfaction in the losses in many European game farms that birds which unlocks deviations in their breed wild birds in captivity (in an aviary for behavior. release/displacement and shooting). (3, 4) The relevance of the problem is also associated The etiology of feather pecking and with the increased number of wild birds bred cannibalism is multifactorial with two main commercially for game meat production (5-7). groups of factors being involved: extrinsic and Despite the extensive research in the field, this intrinsic (9-11). bird welfare problem is still relevant as far as I.Extrinsic factors. External factors are those the humane treatment of the birds goes (2, 8). that don’t depend on the species of bird – The goal of this review is to provide a factors outside of the organism that causes ______injurious pecking. There are three abiotic *Correspondence to: Slavko Nikolov, Department of Internal Non-infectious Diseases, Faculty of groups assigned: nutritional factors, factors of Veterinary Medicine; Trakia University, Students’ the environment (light, temperature, sound, Campus 6015 Stara Zagora, Bulgaria, GSM: and air), and conditions of breeding (spatial +359897880597, e-mail: [email protected]

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NIKOLOV S., et al. parameters, type of system and enrichment of placement of proteins from animal sources the conditions of breeding). (fish flour, meat, and bone flour or sources of milk proteins, vit. B12) lowers the onset of 1.Nutritional factors: These factors play a injurious pecking (23). Meanwhile, the content key role in the potential development of of plant proteins in the ration has a negative feather pecking (FP) as the specific way of effect on birds since they contain feeding is strongly connected with cannibalism phytoestrogens which increase the plasma in birds (12, 13). concentrations of estradiol and cause the 1.1 Composition of the ration: It is known behavior of feather pecking and cannibalism that the composition of the ration influences (23). damaging behavior in birds (14-16). The 1.1.2 Content of minerals: High levels of nutritional deficit stimulates injurious pecking magnesium in the bird ration lower injurious in game birds (5, 6), in the exploitation of pecking tendencies (1). Severe feather pecking domestic birds it can increase feather pecking has an increase in cases of nutritional deficit of and cannibalism (1). The amount of protein, magnesium in the ration (17). The element zinc minerals, energy values, and fibers can has a positive influence on the feathering and influence heavy feather pecking (8). the levels of injurious pecking in birds (1, 20, 1.1.1 Content of proteins and amino acids. 24). The addition of zinc to the ration when The nutritional deficit of raw protein and there is a deficit significantly improves the essential amino acids leads to an increase in condition of the feathering (15, 25). The damaging behavior in birds which results in content of sodium in the diet influences the poor condition of the feathers and higher condition of the feathering and increases the mortality caused by cannibalism (13, 17). activity of the birds as well as injurious - Raw protein: Diets with low content of pecking (1). It is proven that high levels of proteins are connected to an increase in feather selenium are the reason for aggression and pecking and higher mortality rates attributed to higher mortality from cannibalism between cannibalism (13, 18). Diets with an increased adult pheasants as well as a higher mortality content of proteins (casein, gelatine, liver rate in embryos (26). flour, blood flour, soy oil flour, cotton seed, 1.1.3 Content of fibers and roughages: The and others) have a positive effect on the addition of fibers to the diet or feeding feathering and lower injurious pecking (12, roughages can significantly lower injurious 17). pecking in birds (27, 28). When there’s a lack - Amino acids: The sulfur-containing amino or insufficiency of non-starch polysaccharides acids such as methionine and cysteine have an (NSP) the birds acquire them through eating important role in the development of the feathers (29), meaning the levels of feather feathers (18) which is connected to the picking and cannibalism increase (1). A frequency of injurious pecking (19). Ruffled or number of studies confirm that the high inappropriately grown feathers (abnormal content of NSP in the ratio of birds is useful feathering) encourage the behavior of feather for the prevention of injurious pecking (13). pecking and even cannibalism (17). More Providing roughages (green clover and beech important is the role of the aromatic amino leaves) in pheasants (30) or grass, beets, acids: tryptophan (TRP), phenylalanine (PHE) carrots in chickens lowers injurious pecking and tyrosine (TYR) which are precursors for (31). the synthesis of monoamine neurotransmitters 1.1.4 Energy content: The energy content in (serotonin and dopamine) and catecholamines the ration can also influence injurious pecking (noradrenaline) which are responsible for the (13). The increase of energy content in the regulation of injurious pecking in birds (10) – ration increases the reception of energy and reviewed in factors of CNS. Additional leads to higher mortality from cannibalism and placement of the amino acids lysine (17) and a significant worsening of the feathering (18). arginine (20) also supports the improvement of Rations with low energy content increase the feathering and lowers the levels of feather consuming behavior and the amount of pecking and cannibalism in pheasants and gray consumed forage which lowers the possibility partridges (21, 22). of feather pecking development or cannibalism - Value of origin of the protein source: The (14). replacement of animal protein with one of plant origin increases the frequency of feather pecking and cannibalism. (12, 17). Additional

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NIKOLOV S., et al. 1.2 Nutritional strategies: feathering (41) and they also influence the 1.2.1 Changes in the ration: It is known that activity of injurious pecking (35). birds are very sensitive towards sudden 2.2 Temperature factor: Providing an changes in their ration (11, 32). Changes in the appropriate zone of thermal comfort is an ration increase injurious pecking (28, 33) and important component of the welfare of birds vent pecking (34). and lowers the behavior of feather pecking (11, 1.2.2 Physical form of the forage and size of 16). Low as well as high temperatures lead to the pieces: The physical form of the forage thermal stress and the birds develop injurious being fed (mash, crumbs, or pellets) and the pecking (32, 37). distribution of particles in the ration of the 2.3 Sound factor: The connection between birds can influence the behavior of feather sound and stress in birds (11, 37) has been pecking due to changes in the time needed to proven in means of different waves of sound consume the forage (11, 31). Feeding with dust leading to various behavioral reactions on their form forages such as mash lowers injurious behalf (35). Strong mechanical noise leads to pecking while feeding with granulated forage negative effects in birds; causes stress and in increases the frequency of damaging behavior after effect the development of injurious (9, 14). pecking (9, 36). 2.4 Air factor: Good ventilation and quality of 2. Factors of the environment: The air in the breeding areas are significant for the interaction between the abiotic factors such as welfare of the birds (8, 42). Poor ventilation of light, temperature, sound and air quality can air leads to a buildup of harmful gases. When significantly influence the development of there is an increase in the concentration of damaging behavior (15, 35). Factors of the carbon dioxide (16), hydrogen sulphide, or environment can create stressful situations for ammonia the damaging behavior increases (35, the birds because they are much more sensitive 39). Mechanical pollution and dusting in the than humans to changes in the environment air of breeding areas are also a factor leading (16, 36). That way birds try to overcome the to injurious pecking (37, 42). unfortunate conditions and they resort to injurious pecking as a way of coping (11, 37). 3. Factors of breeding conditions/ homing 2.1 Light factor: Contrary to humans that climate: The homing climate is of great have trichromacy vision birds have importance for the development of feather tetrachromatic color vision and are capable of pecking and cannibalism in birds. It depends perceiving the UV part of the light spectrum on the parameters of the area and the division (9, 36). Birds are highly sensitive to light and between the birds, the type of breeding system its parameters: light intensity, duration of the and environment enrichment (available photoperiod, and wavelength. They can bedding, perch stands, types of drinkers and influence injurious pecking (38, 39). feeders and aerated breeze blocks (13, 38, 39). 2.1.1 Intensity of light: Overexposure to light/ 3.1 Spatial parameters and division of the the higher light intensity increases the feather birds: The characteristics of the limited areas pecking behavior and cannibalism in birds (9, such as density of breeding and size of the 35). On thecontrary low intensity of light group can significantly change the way birds lowers injurious pecking (16, 36). cooperate between each other and how they 2.1.2 Photoperiod: Breeding in conditions of use the resources they’ve been given (16, 43) permanent (24 hour) light day of newly which includes the free space and size of the hatched chickens significantly increases confinement (44). injurious pecking in adult age (8, 40). The 3.1.1 Density of breeding: The density of normal photoperiod which can be achieved by breeding is the main factor that influences the use of dark brooder significantly decreases injurious pecking in game birds (5, 6, 30). The injurious pecking in birds. Those way active higher density of breeding increases injurious chickens can be divided from inactive chickens pecking. (9, 32) (36). 3.1.2 Size of the group: The size of the group 2.1.3 Wavelength: The specific wavelength in has a significant influence on cannibalism in the color spectrum – red and blue light (11) as pheasants (4, 30). Feather pecking and forms well as UV light influences the behavior of of cannibalistic behavior are most commonly feather pecking and cannibalism (38, 39). They seen in birds bred in large groups (10, 13). The change the perception of the birds towards smaller size of the group and usage of colors, details and reflective capabilities of the conventional and furnished cages are

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NIKOLOV S., et al. connected to lower levels of injurious pecking we observe a decrease in productivity and compared to the big sized bird groups typical higher mortality: feather pecking, cannibalism for free systems of breeding – look at the types and an increase in the manifestation of fear of breeding systems (43, 45). (47). That stands as well for pheasants bred in 3.1.3 Usage of free space: The bigger access conventional cages which show behavioral to a free area or a prolonged period on the disturbances: aggression, cannibalism and outside severely reduces injurious pecking in higher mortality (7, 50). birds (44, 46). 3.3 Enrichment of the environment: An 3.1.4 Influence between spatial parameters: alternative way to prevent damaging behavior The three factors are in correlation since in birds is the enrichment of the environment density is a direct consequence of change in (11, 12). the size of the group or the size of the 3.3.1 Influence of the feeders and drinkers: confinement which makes it harder to The type of feeding device and the way food is determine the individual influence of every provided highly influences the bird’s behavior factor leading to injurious pecking on its own (27). Birds that have access to operating, (36, 44). The bigger number of birds limits the hanging or segmented mechanical feeders possibility of movement and spreading of the develop a high sense of competitiveness and individuals (32) which contributes to the usage disappointment in the feeding which leads to of less free space while in small groups it is the injurious pecking (16). Using a mixed type opposite (46). Breeding of birds in high density feeder lowers the feeding competitiveness and with little space and a big number of birds damaging behavior (36). Satisfying the water increases the possibility of birds interacting needs and hydration of the birds is an with each other (11). The small confinements important moment because it can onset with low density and a small number of birds injurious pecking (11). Usage of drinkers from use the area and activity in the most balanced the bell type increases feather pecking (34, 43). way which lowers feather pecking and Nipel drinkers decrease injurious pecking in cannibalism most effectively (44). birds (9). 3.2 Type of breeding system: A base for good 3.3.2 Availability of bedding/ nutritional welfare of the birds is to have them placed in substrate: Ensuring that there is a substrate conditions that are specific for each individual with a good quality is important for the welfare species, as close as possible to their natural of birds and makes the job of the bird breeders habitat (7, 47). Breeding of birds in closed easier (11, 51). It is widely acclaimed that the spaces (cage or no cage), outside (aviary cages feathering is in better condition when there is with a yard) or in bio farms and the way they bedding available because it allows the normal are managed directly interferes with the behavior of digging and bathing in it (8, 16). development of damaging behavior (32, 38, Making bedding available in young age 40). significantly decreases injurious pecking in 3.2.1 Systems of free breeding in a closed adult age (9, 17). An increase in injurious confinement: Feather pecking is seen in all pecking in adult birds is seen in cases of lack systems of bird breeding (12, 36) but is a main of bedding at an early age (28) or limiting its problem in free living systems (43, 48) where amount (38). the pecking birds have access to a large 3.3.3 Influence of bird perches: Providing an number of potential victims and the culprits adequate and timely access to perches is can’t be easily identified (45). important for birds in connection to feather 3.2.2 Systems of free breeding outside: pecking and cannibalism (40, 47). The perches Breeding outside and the duration of time in help with the development of the skeleton and the sun (33) can influence the onset of muscles and also make movement easier injurious pecking (36, 39). The placement of (increase activity) for the birds and encourage natural or superficial covers over the bird their natural behavior (7). Perches also aviary in birds bred outside lowers the onset of increase the amount of used vertical space and feather pecking (46). their presence ensures the possibility of escape 3.2.3 Systems of conventional cage breeding: from unwanted social engagements or In cage breeding where the size of the group is unfortunate conditions of the environment (11, smaller the order of hierarchy is more stable 32). and problems with feather pecking develop 3.3.4 Influence of aerated breeze blocks: less (45, 49). In domestic birds bred in a Enrichment of the environment through the conventional cage system with higher density placement of aerated breeze blocks lowers the 380 Trakia Journal of Sciences, Vol. 18, № 4, 2020

NIKOLOV S., et al. onset of injurious pecking in birds (9). It stereotypical behavior is significantly higher in encourages the natural pecking of the ground males compared to female pheasants. The and dulling of the beak which strongly higher percentage of stereotypical behavior in influences damaging behavior (28, 36). pheasants is monitored in the early hours (peaking at 12 h) while in males the level of II. Intrinsic factors. Intrinsic factors are those stereotypical behavior is mainly found at 13 h that depend on the bird – factors of the (50). Also even a minimal onset of organism that influence injurious pecking. stereotypical behavior leads to injurious Seven groups of biotic factors fall into the pecking (49). category: social, sex, age, stress, central 1.4 Influence of maternal behavior on the nervous, hereditary, and immunological. newly hatched: The conditions during which 1. Behavioral/social factors: Behavioral the eggs were hatched as well as the period of characteristics of the individuals lead to a incubation and early history of life can have variety of interactions between birds in their serious consequences on the behavioral social group which leads to damaging development of young birds (40). It has been influence (16, 40). proven that chickens raised by a hatcher hen 1.1 Social training (imitating behavior): have lower mortality rates due to feather Social training allows behavioral innovations pecking and cannibalism (8). Chickens raised to spread fast among the population and that by a hatcher hen are less scared and have way the adaptation towards different higher social motivation in adult age (40). environments and unpredictable conditions is Taking away the mothering care from young made easier (51). Birds can change their birds can have serious consequences: a higher behavior through social transfer (imitating one onset of injurious pecking (8). It is interesting another) while they watch other individuals that birds that have undergone stress in young from their species (12). At first injurious age have higher prevalence to develop feather pecking is done by a small number of birds in pecking behavior in adult age (57). the group but it is easily spread (17). It is confirmed that social training makes it easier 2. Sex factors: Significant differences have and faster for onsets of feather pecking (19) been proven between the two sexes in relation and cannibalism in domestic and game birds to to the prevalence for injurious pecking; male develop (52). individuals are less likely to develop feather 1.2 Sexual behavior: Pecking of female pecking behavior than females (12). It is pheasants from male individuals during mating determined that the presence of a cock in the is a form of aggressive behavior (50). The act herd of hens is a factor which lowers feather of mating during the day is influenced by the pecking (46). A higher onset of pecking and cycle of egg laying because mating decreases cannibalism between male pheasants has been around the period of laying (53). Pheasants and observed (3, 50). quails usually lay their eggs in the afternoon 2.1 Sex hormones: Steroid hormones – (compared to domestic chickens which lay estrogens and androgens have a great impact eggs in the morning) so the act of mating is in on the behavior and injurious pecking in birds the morning and early evening (54). The speed (1). The female sex hormones increase feather of mating is increased in the evening (19 h) pecking and cannibalistic behavior in birds which is at the same period of time as the act (12). A counter tendency of influence over of cannibalism from the male to the female he feather pecking and cannibalism in birds is had mated with. Different models of observed with male sex hormones although it aggressive behavior have been observed in the decreases egg production (8). Low doses of females during the day and their culmination is testosterone lower injurious pecking but in at the same time (19 h) and is connected to high doses as well as in combination with cannibalism (50, 53). estradiol they are significantly increased (12). 1.3 Stereotypical behavior: Stereotypical It is proven that testosterone increases the behavior is developed in unpredictable aggressive and sexual behavior in domestic situations in which the individual doesn’t have chickens (17). control over the environment and that leads to 2.2 The role of sex hormones on disappointment or dissatisfaction (55). Feather embryogenesis: The yolk of the egg contains pecking has characteristics similar to significant amounts of steroid hormones such obsessive-compulsive disorder in humans as estrogens and androgens (1) which can have (trichotillomania) and mice (56). The level of a longstanding effect on the development of

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NIKOLOV S., et al. the brain and the behavior of the bird embryo mental instability and increase in the levels of (58). The collection of hormones in the yolk is feather pecking in adult age (12). a mechanism with which the mother can adapt the development of her offspring to the current 5. Factors of the central nervous system: conditions of the environment (8). The The nervous system regulates the behavior in hormonally mediated effects of the mother are birds directly and the neurohumoral regulates important for the development of injurious injurious pecking (1, 15). The behavioral pecking in the offspring (1). The effect of characteristics connected to the strong testosterone in eggs speeds up the development susceptibility to damaging behavior and the of the chickens and makes them more influence of stress are determined by aggressive and competitive than the others differences in neurophysiology and the birds’ (59). temperament (57), meaning the serotonin (61, 65, 66), dopamine systems (67, 68) and 3. Age factor: The level of onset of feather noradrenaline (8, 12, 64) which have cause- pecking depends on the age of the birds (9, effect connection to the onset of feather 38). In young age the lighter form of feather pecking and cannibalism (69). pecking dominates (48). It serves as learning 5.1 Influence of serotonin (5-HT): The behavior and is a form of social contact (28). serotonin activity plays a key role in the The heavy forms of feather pecking and physiological characteristics of injurious cannibalism develop in adult age which leads pecking (10, 65). The division of serotonin to worse feathering in birds in adult age (15, fibers in the bird brain controls the influence of 29). serotonin (5-HT) over fear and social behavior (62, 66, 69). It is proven that 5-HT has an 4. Factors of fear and stress: Unfortunate important role in the response to stress conditions can lead to stress in birds (10, 51). situations in chickens during manipulations or The high sensitivity towards stress comes from moving to an unknown environment (11, 68). high levels of fear (9). The behavioral 5.2 Influence of dopamine: Dopamine characteristics of lone individuals or different conduction of nervous impulses in the brain species of birds towards manifestations of fear also has a key role in the neurophysiological and stress also play a role in the development characteristics of injurious pecking (12, 67). of feather pecking and cannibalism (1) in Dopamine improves the capability of coping turkeys (60) and ducks (61). Fear is the with fear and stress and leads to lower feather probability of the individual being easily pecking levels (1, 70). Bird individuals are scared (17). Birds who demonstrate higher different from each other as far as dopamine levels of fear resort to feather pecking behavior synthesis in the CNS goes. Those that manifest (12). A connection between fear and injurious more feather pecking have lower plasma levels pecking of feathers has been determined (62). of dopamine in their blood (64, 65, 68). Birds Feather pecking can increase the sense of fear that manifest injurious pecking have less and on the contrary fear can also be a precursor dopamine receptors or the receptors are to feather pecking development (9). It is blocked which leads to an increase in pleasure proven that different market lines of hens are gained by feather pecking (11). different as far as fear levels, sensitivity to 5.3 Influence of noradrenalin (NA): stress and aptitude to heavy feather pecking go Catecholamines have an important role in (62). some behavioral pathology in bird species (8, - Hormone of stress (corticosterone): The 12). It is determined that when birds influence of stress hormones and more manifesting injurious pecking are a subject of specifically corticosterone is significant for the stress they respond with a higher plasma levels development of injurious pecking as well as of NA (65) in comparison to those with lower feather pecking and cannibalism in birds (1). levels of feather pecking which respond to The increase of plasma concentration of stress with lower levels of NA (64). corticosterone increases feather pecking and cannibalism in birds (63). It is determined that 6. Genetic/ hereditary factors: Differences in the levels of main corticosterone are higher in feather pecking levels, quality of the feathering birds demonstrating more injurious pecking and mortality from cannibalism between (64, 65). Adding corticosterone to the forage of different populations are determined by the growing birds leads to simulation of chronic genetic fund of birds (15, 71). Feather pecking stress and leads to lower growth rate, increase is inherited in the offspring as a “hereditary

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NIKOLOV S., et al. factor” (8, 48). There is a significant that don’t develop injurious pecking have difference between the genetic origin of the quick and transient behavioral and birds connected to the quality of feathering, physiological changes with less negative skin lesions and cannibalism (16, 57). effects of weight gain, organ development and Molecular studies show that the genetic fund internal temperature when exposed to of feather pecking is poligenius (72) while immunological stress-LPS immunological cannibalism and aggression in a combination probe (15, 60). Birds with high levels of can be influenced by one or a few main genes feather pecking have a more turbulent response (73, 74). to an immunological probe and a smaller 6.1 Genotypic manifestation (QTL-genome number of white blood cells after vaccination region): Feather pecking in certain breeds of (43, 76). egg laying hens (48, 74) is connected to genome regions (QTL) which are responsible CONCLUSION for behavior (15). QTL regions are connected Unbalanced and deficit feeding especially in to complicated behavioral traits of feather terms of aromaaminoacids (TRP, PHE, TYR) pecking and cannibalism and the genes for fear and non-starch polysaccharides (NSP) in the and anxiety in birds (1). The suggestive locus ration have a significant impact in the etiology QTL is identified in mild feather pecking cases of injurious pecking. The abiotic factors (light, in young individuals and in heavy feather temperature, sound and air) have a role in pecking case in adults (73). The presence of damaging behavior, the unfortunate factors of these additive genetic effects is the base of the environment cause stressful situations in feather pecking behavior determined through birds and as a coping mechanism they develop hereditary traits (71). injurious pecking. The conditions of breeding, 6.2 Phenotypic manifestation – the the spatial parameters and the enrichment of importance of pigmentation of the the environment are very important for the feathering: The condition of the feathering is birds because they give the opportunity for connected to genome regions QTL identical close contact and a variety of interactions with gene (PMEL17) for “white-dominant” between them which includes damaging color (2, 72). Pigmentation of the feathers as a behavior. The behavioral characteristics of hereditary sign has a significant influence on individuals lead to different relationships the risk of turning the bird into a victim between birds in their social group which lead because the pigmented individuals are more to poor social motivation and dissatisfaction sensitive to injurious pecking than whites (8, which onsets injurious pecking. On the other 48). The higher frequency of feather pecking is hand heredity, the individuality of the type of examined from pigmented towards white birds nervous system – transmissions of impulses in which is due to the fact that there is a bigger the brain (5-НТ, DA, NA), the immune contrast between the dark feathers and light reactivity and stress (corticosterone) regulate skin (12, 74). injurious pecking in individual birds. The connection between extrinsic and intrinsic 7. Immunological factors: A connection factors is significant and they can’t be between immune reactivity and stress in birds interpreted on their own and independently with damaging behavior – feather pecking and from one another. cannibalism has been proven (9, 75). Phenotypic and genotypic onsets of heavy REFERENCES feather pecking have a connection to the 1. Rodenburg, T.B., M.M. van Krimpen, I.C. immune system. Birds that manifest more de Jong, E.N. de Haas, M.S. Kops, B.J. injurious pecking have higher levels of specific Riedstra, R.E. Nordquist, J.P. Wagenaar, humoral immunity (75, 76). There are M. Bestman and C.J. Nicol, The prevention significant differences between the populations and control of feather pecking in laying of birds demonstrating injurious pecking and hens: identifying the underlying principles. their physiological response to regulation from Worlds Poultry Science Journal: 69, 361– the adrenal glands and the immune system 373, 2013. (63). The birds are exposed to endotoxins 2. Jensen, P., Genetics and genomics of (different antigens) in the air, forage, water, animal welfare. In: Mench, J.A. (Ed.), feces and vaccines and their effect is different Advances in Agricultural Animal Welfare. according to the dosage, time of exposure and Science and Practice, Elsevier, Oxford. pp. overall condition of the individual (75). Birds 25-48, 2018.

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