Scientific report updating the EFSA opinions on the welfare of broilers and broiler breeders. Supporting Publications 2012.EN-295. Sub-report A

The EFSA AHAW panel is requested to develop several scientific opinions concerning animal based measures to assess the welfare of livestock animals. The main objective of this report is to review the broiler welfare literature to identify gaps and potential areas to strengthen and update three SCAHAW and EFSA opinions: i) The welfare of chickens kept for meat production (broilers) (SCAHAW, 2000), ii) Influence of genetic parameters on the welfare and resistance to stress of commercial broilers (EFSA, 2010), iii) Welfare aspects of the management and housing of the grand-parent and parent stocks raised and kept for breeding purposes (EFSA, 2010). The literature review was done by a group of authors and reviewers, under the supervision of an editorial team. A large number of new scientific references are quoted. Regarding the first and oldest opinion, this review presents 47 amended and new conclusions. In addition, it suggests twelve new recommendations and proposes a list of hazards. Especially the paragraphs on behavioural restriction, light, stocking density and environmental enrichment are updated with new information from a large number of new scientific references. Regarding the second opinion, nine new conclusions are proposed. Recommendations of the previous EFSA report are further supported by new information, and one new recommendation is a suggestion to further study the role of incubation conditions on welfare issues such as gait abnormalities, thermal discomfort and ascites. A limited number of new hazards are proposed. Regarding the third opinion, four new conclusions are proposed. Recommendations of the previous EFSA report are also in this case further supported by new information. One new recommendation is a suggestion to further study the impact of management on forced mating behaviour. A couple of new hazards are proposed.

[1]  A. Villagrá,et al.  Evaluation of sludge from paper recycling as bedding material for broilers. , 2011, Poultry science.

[2]  A. Hall.  The Effect of Stocking Density on the Welfare and Behaviour of Broiler Chickens Reared Commercially , 2001, Animal Welfare.

[3]  G. Díaz,et al.  Effect of graded levels of dietary nickel and manganese on blood haemoglobin content and pulmonary hypertension in broiler chickens. , 1996, Avian pathology : journal of the W.V.P.A.

[4]  C. B. Annett,et al.  The impact of nutrient density, feed form, and photoperiod on the walking ability and skeletal quality of broiler chickens. , 2007, Poultry science.

[5]  I. Estevez,et al.  Use of cool perches by broiler chickens. , 2002, Poultry science.

[6]  Linda J. Keeling,et al.  Definition of criteria for overall assessment of animal welfare , 2007, Animal Welfare.

[7]  I. Zulkifli,et al.  The effects of regular visual contact with human beings on fear, stress, antibody and growth responses in broiler chickens , 2002 .

[8]  P. Koene,et al.  Behaviour of fast- and slow growing broilers to 12 weeks of age and the physical consequences , 2003 .

[9]  R. C. Newberry,et al.  Use of pen space by broiler chickens: effects of age and pen size. , 1990 .

[10]  L. Collins,et al.  Non-intrusive tracking of commercial broiler chickens in situ at different stocking densities , 2008 .

[11]  L. Rogers,et al.  Different responses in two strains of chickens (Gallus gallus) in a magnetic orientation test , 2008, Animal Cognition.

[12]  S. Rahimi,et al.  Control of ascites mortality and improved performance and meat shelf-life in broilers using feed adjuncts with presumed antioxidant activity , 2011 .

[13]  T. Morris,et al.  An analysis of the hypothesis that amino acid requirements for chicks should be stated as a proportion of dietary protein , 1999 .

[14]  Davis Nj,et al.  Preferences of growing fowls for different light intensities in relation to age, strain and behaviour , 1999 .

[15]  M. R. Reddy,et al.  Evaluation of Growth, Carcass, Immune Response and Stress Parameters in Naked Neck Chicken and Their Normal Siblings under Tropical Winter and Summer Temperatures , 2011 .

[16]  J. Thaxton,et al.  Stocking density effects on growth performance and processing yields of heavy broilers. , 2005, Poultry science.

[17]  Y.P. Lee,et al.  Daytime behavioural patterns of slow-growing chickens in deep-litter pens with perches , 2007, British poultry science.

[18]  J. L. Campo,et al.  Effects of specific noise and music stimuli on stress and fear levels of laying hens of several breeds , 2005 .

[19]  M. Macleod,et al.  Genotype, dietary manipulation and food allocation affect indices of welfare in broiler breeders , 2004, British poultry science.

[20]  R. Julian,et al.  Right ventricular failure and ascites in broiler chickens caused by phosphorus-deficient diets. , 1986, Avian diseases.

[21]  F. Sirri,et al.  Assessment of a global positioning system to evaluate activities of organic chickens at pasture , 2010 .

[22]  C. M. Wathes,et al.  Aerial emissions from poultry production , 1998 .

[23]  J. Feddes,et al.  Broiler performance, body weight variance, feed and water intake, and carcass quality at different stocking densities. , 2002, Poultry science.

[24]  C. Ruiz-Feria,et al.  L-arginine and antioxidant vitamins E and C improve the cardiovascular performance of broiler chickens grown under chronic hypobaric hypoxia. , 2010, Poultry science.

[25]  L. Waldenstedt.  Nutritional factors of importance for optimal leg health in broilers : A review , 2006 .

[26]  W. Dozier,et al.  Broiler responses to reduced-protein diets supplemented with valine, isoleucine, glycine, and glutamic acid , 2010 .

[27]  W. D. Weaver,et al.  Effect of early feed restriction on growth, feed conversion, and mortality in broiler chickens. , 1992, Poultry science.

[28]  E. Russek-Cohen,et al.  Effects of density and perch availability on the immune status of broilers. , 2002, Poultry science.

[29]  M. Christman,et al.  Short- and long-term movement patterns in complex confined environments in broiler chickens: the effects of distribution of cover panels and food resources. , 2010, Poultry science.

[30]  J. Thaxton,et al.  Stocking density and physiological adaptive responses of broilers. , 2006, Poultry science.

[31]  R. Gous,et al.  Welfare-compliant lighting regimens for broilers. , 2010 .

[32]  B. B. Jensen,et al.  Influence of whole wheat and xylanase on broiler performance and microbial composition and activity in the digestive tract. , 2004, Poultry science.

[33]  Andrew Butterworth,et al.  Leg Disorders in Broiler Chickens: Prevalence, Risk Factors and Prevention , 2008, PloS one.

[34]  J. Faure,et al.  Influence of increased environmental complexity on leg condition, performance, and level of fearfulness in broilers. , 2002, Poultry science.

[35]  C. Donnelly,et al.  Environmental and management factors affecting the welfare of chickens on commercial farms in the United Kingdom and Denmark stocked at five densities. , 2005, Poultry science.

[36]  K. Yamazaki,et al.  Footpad dermatitis in broiler chickens in Japan. , 2011, The Journal of veterinary medical science.

[37]  C. Parsons,et al.  The effects of whole grains on nutrient digestibilities, growth performance, and cecal short-chain fatty acid concentrations in young chicks fed ground corn-soybean meal diets. , 2009, Poultry science.

[38]  G. Wang,et al.  Expression analysis of global gene response to chronic heat exposure in broiler chickens (Gallus gallus) reveals new reactive genes. , 2011, Poultry science.

[39]  M. Picard,et al.  Whole cereal grains in broiler nutrition: the come back? , 1998 .

[40]  B. Fairchild,et al.  Footpad dermatitis in poultry. , 2010, Poultry science.

[41]  P. Hemsworth.  Human–animal interactions in livestock production , 2003 .

[42]  R. Marchant-Forde,et al.  Different effects of infrared and one-half hot blade beak trimming on beak topography and growth. , 2010, Poultry science.

[43]  S. Avendaño,et al.  Genetic parameters of feeding behavior traits and their relationship with live performance traits in modern broiler lines. , 2011, Poultry science.

[44]  S F Bilgili,et al.  Effect of light intensity and photoperiod on live performance, heterophil-to-lymphocyte ratio, and processing yields of broilers. , 2007, Poultry science.

[45]  P. Groves,et al.  Incubation can affect broiler leg strength. , 2011 .

[46]  C. G. Reenen,et al.  Strength of preference for dustbathing and foraging substrates in laying hens , 2007 .

[47]  W. B. Roush,et al.  A Review of Lighting Programs for Broiler Production , 2006 .

[48]  S. Gomis,et al.  Influence of dietary nutrient density, feed form, and lighting on growth and meat yield of broiler chickens. , 2007, Poultry science.

[49]  A. Ben David,et al.  Comparative effects of added sodium chloride, ammonium chloride, or potassium bicarbonate in the drinking water of broilers, and feed restriction, on the development of the ascites syndrome. , 1998, Poultry science.

[50]  G. Erf,et al.  Effect of intravenous endotoxin on blood cell profiles of broilers housed in cages and floor litter environments. , 2003, Poultry science.

[51]  S. Yahav,et al.  The effects of feed restriction and ambient temperature on growth and ascites mortality of broilers reared at high altitude. , 2010, Poultry science.

[52]  D. Qujeq,et al.  Effects of supplementation of canola meal-based diets with arginine on performance, plasma nitric oxide, and carcass characteristics of broiler chickens grown at high altitude. , 2011, Poultry science.

[53]  C. Bunchasak.  Role of dietary methionine in poultry production , 2009 .

[54]  V. Ravindran,et al.  Influence of stocking density on the performance, carcass characteristics and selected welfare indicators of broiler chickens , 2004, New Zealand veterinary journal.

[55]  M. Türkyılmaz.  The Effect of Stocking Density on Stress Reaction in Broiler Chickens during Summer , 2008 .

[56]  S. Kestin,et al.  Effects of age and stocking density on leg weakness in broiler chickens. , 2000, Poultry science.

[57]  W. Bessei,et al.  The influence of stocking density on the behaviour of featherless and normally-feathered broilers under hot ambient temperature. , 2010 .

[58]  F. Levenez,et al.  Effects of stocking density on the growth performance and digestive microbiota of broiler chickens. , 2011, Poultry science.

[59]  I. Muchnik,et al.  Early warning indicators for hock burn in broiler flocks , 2010, Avian pathology : journal of the W.V.P.A.

[60]  R. Kwakkel,et al.  Heat stress and feeding strategies in meat-type chickens , 2011 .

[61]  W. Bessei,et al.  The effect of locomotor activity and weight load on bone problems in fast and slow growing chickens. , 2009 .

[62]  Linda J. Keeling,et al.  Neighbourhood analysis as an indicator of spatial requirements of broiler chickens , 2011 .

[63]  X. Manteca,et al.  Stocking density and stress induction affect production and stress parameters in broiler chickens , 2009, Animal Welfare.

[64]  G. Rottinghaus,et al.  A sudden death syndrome induced in poults and chicks fed diets containing Fusarium fujikuroi with known concentrations of moniliformin. , 1997, Avian diseases.

[65]  K. Schwean-Lardner,et al.  Impact of daylength on behavioural output in commercial broilers , 2012 .

[66]  B. Ventura.  Effects of barrier perches and stocking density on the behavior, space use, and leg health of the domestic fowl (Gallus gallus domesticus) , 2009 .

[67]  P. Lewis,et al.  Photoperiodic responses of broilers. I. Growth, feeding behaviour, breast meat yield, and testicular growth , 2009, British poultry science.

[68]  F. Sirri,et al.  Survey of chicken rearing conditions in Italy: effects of litter quality and stocking density on productivity, foot dermatitis and carcase injuries , 2008, British poultry science.

[69]  S. Vestergaard,et al.  Relationships between leg disorders and changes in the behaviour of broiler chickens , 1999, Veterinary Record.

[70]  P. Hemsworth,et al.  Human factors affecting the behaviour and productivity of commercial broiler chickens , 2000, British poultry science.

[71]  D. Burt,et al.  Overlap of quantitative trait loci for early growth rate, and for body weight and age at onset of sexual maturity in chickens. , 2011, Reproduction.

[72]  M. Gulay,et al.  Effect of Stocking Density on Chick Performance, Internal Organ Weights and Blood Parameters in Broilers , 2011 .

[73]  J. Hess,et al.  Effect of bedding type and transient wetness on footpad dermatitis in broiler chickens , 2011 .

[74]  E. Erdem,et al.  Influence of lighting periods and stocking densities on performance, carcass characteristics and some stress parameters in broilers , 2008 .

[75]  J. Feddes,et al.  Growth performance, carcass characteristics, and the incidence of ascites in broilers in response to feed restriction and litter oiling. , 1999, Poultry science.

[76]  S. Yahav,et al.  Improvement of cold resistance and performance of broilers by acute cold exposure during late embryogenesis. , 2011, Poultry science.

[77]  S. Kestin,et al.  A note on the effects of perches and litter substrate on leg weakness in broiler chickens. , 2000, Poultry science.

[78]  I. Estevez,et al.  Effects of barrier perches and density on broiler leg health, fear, and performance. , 2010, Poultry science.

[79]  N. Imaeda.  Influence of the stocking density and rearing season on incidence of sudden death syndrome in broiler chickens. , 2000, Poultry science.

[80]  C. Phillips,et al.  The effects of color and intensity of light on behavior and leg disorders in broiler chickens. , 1997, Poultry science.

[81]  P. Kettlewell,et al.  Temperature gradients in trailers and changes in broiler rectal and core body temperature during winter transportation in Saskatchewan , 2010 .

[82]  M. Dawkins,et al.  The Effect of a ‘Freedom Food’ Enrichment on the Behaviour of Broilers on Commercial Farms , 2001, Animal Welfare.

[83]  R. Çibik,et al.  The influence of different lighting programs, stocking densities and litter amounts on the welfare and productivity traits of a commercial broiler line. , 2010 .

[84]  I. Duncan,et al.  The importance of rest in young domestic fowl , 2007 .

[85]  J. Hutchinson,et al.  The effects of selective breeding on the architectural properties of the pelvic limb in broiler chickens: a comparative study across modern and ancestral populations , 2010, Journal of anatomy.

[86]  P. Koene,et al.  Walking behaviour of heavy and light broilers in an operant runway test with varying durations of feed deprivation and feed access , 2007 .

[87]  I. Estevez,et al.  Use of space in the domestic fowl: separating the effects of enclosure size, group size and density , 2008, Animal Behaviour.

[88]  K. Azad,et al.  Effect of Chronic Heat Stress on Performance and Oxidative Damage in Different Strains of Chickens , 2010 .

[89]  F. Robinson,et al.  Effects of increasing photoperiod length on performance and health of broiler chickens. , 1991, British poultry science.

[90]  H. Howland,et al.  Diurnal illumination patterns affect the development of the chick eye , 2000, Vision Research.

[91]  E. Decuypere,et al.  The Broiler Breeder Paradox: ethical, genetic and physiological perspectives, and suggestions for solutions , 2010, British poultry science.

[92]  J. Guy,et al.  Effect of enrichment with Pecka-Blocks™ on the behaviour and feather condition of commercially-reared broilers , 2003 .

[93]  Y. Wang,et al.  Effect of atmospheric ammonia on growth performance and immunological response of broiler chickens. , 2010 .

[94]  B. Svihus,et al.  Effect of feeding whole cereals on performance, starch digestibility and duodenal particle size distribution in broiler chickens , 2002, British poultry science.

[95]  W. Bessei.  Welfare of broilers: a review , 2006 .

[96]  P. Hemsworth,et al.  Behavioural responses to humans and the productivity of commercial broiler chickens , 1994 .

[97]  S. Lea,et al.  Adaptation by learning: its significance for farm animal husbandry , 2007 .

[98]  J. Thaxton,et al.  Role of ascorbic acid in chicks exposed to high environmental temperature. , 1985, Journal of applied physiology.

[99]  H. M. Edwards.  Effects of thiuram, disulfiram and a trace element mixture on the incidence of tibial dyschondroplasia in chickens. , 1987, The Journal of nutrition.

[100]  H. Gunnink,et al.  Pilotstudie naar welzijnsaspecten van kammen dubben bij hanen van legrassen = Pilot study welfare implications of dubbing combs of cockerels of Leghorn parent stock , 2011 .

[101]  H. M. Edwards.  Efficacy of several vitamin D compounds in the prevention of tibial dyschondroplasia in broiler chickens. , 1990, The Journal of nutrition.

[102]  P. Sørensen,et al.  Feed and strain effects on the use of outdoor areas by broilers , 2003, British poultry science.

[103]  I. Estevez,et al.  Behavior of the domestic fowl in the presence of vertical panels. , 2001, Poultry science.

[104]  M. Rezaei,et al.  The Effect of Intermittent Lighting Schedule on Broiler Performance , 2005 .

[105]  R. Baines,et al.  Water consumption in broiler chicken: a welfare indicator , 2007 .

[106]  M. Koci,et al.  Maternal antibody transfer to broiler progeny varies among strains and is affected by grain source and cage density. , 2011, Poultry science.

[107]  M. Groenen,et al.  The use of blood gas parameters to predict ascites susceptibility in juvenile broilers. , 2010, Poultry science.

[108]  I. Estevez,et al.  Economic and welfare benefits of environmental enrichment for broiler breeders. , 2008, Poultry science.

[109]  N. Sellier,et al.  Heritability of digestibilities and divergent selection for digestion ability in growing chicks fed a wheat diet. , 2004, Poultry science.

[110]  J. Sibley,et al.  Influence of bedding material on footpad dermatitis in broiler chickens , 2009 .

[111]  C. Nicol,et al.  Development of spatial memory in occlusion-experienced domestic chicks , 2004, Animal Behaviour.

[112]  E. Decuypere,et al.  Is the mechanisation of catching broilers a welfare improvement? , 2006, Animal Welfare.

[113]  I. Estevez,et al.  Influence of vertical panels on use of space by domestic fowl. , 2001, Applied animal behaviour science.

[114]  A. Valros,et al.  Development of perching behaviour in chicks reared in enriched environment , 2006 .

[115]  A. Mujahid.  Nutritional Strategies to Maintain Efficiency and Production of Chickens under High Environmental Temperature , 2011 .

[116]  R. Jones.  Environmental enrichment: the need for practical strategies to improve poultry welfare. , 2004 .

[117]  D. Denbow,et al.  Utilization of phytate phosphorus and calcium as influenced by microbial phytase, cholecalciferol, and the calcium: total phosphorus ratio in broiler diets. , 1997, Poultry science.

[118]  C. Donnelly,et al.  Chicken welfare is influenced more by housing conditions than by stocking density , 2004, Nature.

[119]  D Berckmans,et al.  Effects of different target trajectories on the broiler performance in growth control. , 2008, Poultry science.

[120]  W. Bessei,et al.  Bone development and activity in chickens in response to reduced weight-load on legs , 2002 .

[121]  S. Kestin,et al.  Meal feeding is more effective than early feed restriction at reducing the prevalence of leg weakness in broiler chickens. , 1999, Poultry science.

[122]  O. Halevy,et al.  The effect of a green and blue monochromatic light combination on broiler growth and development. , 2004, Poultry science.

[123]  B. L. Nielsen,et al.  Effects of qualitative and quantitative feed restriction on the activity of broiler chickens , 2003 .

[124]  V. Ravindran,et al.  Performance and welfare of broilers as affected by stocking density and zinc bacitracin supplementation , 2006 .

[125]  L. Facchin,et al.  Social dispersal by domestic chicks in a novel environment: reassuring properties of a familiar odourant , 2002, Animal Behaviour.

[126]  H. H. Kristensen,et al.  Ammonia and poultry welfare: a review , 2000 .

[127]  C. Phillips,et al.  International approaches to the welfare of meat chickens , 2011 .

[128]  P. Sørensen,et al.  Effect of short fasts on the development of tibial dyschondroplasia in chickens. , 1987, The Journal of nutrition.

[129]  H. Classen,et al.  Photoperiodic effects on performance and leg abnormalities in broiler chickens. , 1989, Poultry science.

[130]  Kei-ichi Tanaka,et al.  The Effects of Intermittent Lighting on Activity of Broiler Chickens , 1998 .

[131]  A. Butterworth,et al.  Measuring and Auditing Broiler Welfare , 2004 .

[132]  P. Hocking,et al.  On-farm assessment of environmental enrichment for broiler breeders , 2006, British poultry science.

[133]  G. Archer,et al.  The effect of light intensity on the behavior, eye and leg health, and immune function of broiler chickens. , 2009, Poultry science.

[134]  J. McLean,et al.  Welfare of Male and Female Broiler Chickens in Relation to Stocking Density, as Indicated by Performance, Health and Behaviour , 2002, Animal Welfare.

[135]  M. Katanbaf,et al.  Primary broiler breeding--striking a balance between economic and well-being traits. , 2010, Poultry science.

[136]  A. Boostani,et al.  Comparison of The Effects of Several FeedRestriction Periods to Control Ascites onPerformance, Carcass Characteristics andHematological Indices of Broiler Chickens , 2010 .

[137]  J L Purswell,et al.  Effect of ambient temperature and light intensity on physiological reactions of heavy broiler chickens. , 2010, Poultry science.

[138]  F. Tuyttens,et al.  Measuring thirst in broiler chickens , 2009, Animal Welfare.

[139]  Prevalence of wet litter and the associated risk factors in broiler flocks in the United Kingdom , 2006, Veterinary Record.

[140]  H. L. Classen,et al.  Day length affects performance, health and condemnations in broiler chickens. , 2004 .

[141]  L. Keeling,et al.  Reduction in feather pecking and improvement of feather condition with the presentation of a string device to chickens , 2005 .

[142]  J. Thaxton,et al.  Stocking density effects on male broilers grown to 1.8 kilograms of body weight. , 2006, Poultry science.

[143]  F. Sirri,et al.  Welfare of broiler chickens , 1996, Animal Welfare.

[144]  M. Picard,et al.  Effects of the Starter Diet, Light Intensity, and Essential Amino Acids Level on Growth and Carcass Composition of Broilers , 2005 .

[145]  Irenilza de Alencar Nääs,et al.  Ambiência aérea em alojamento de frangos de corte: poeira e gases , 2007 .

[146]  J. Ayo,et al.  Behavioral and rectal temperature responses of Black Harco pullets administered vitamins C and E and transported by road during the hot-dry season , 2010 .

[147]  I. Estevez,et al.  Access to Barrier Perches Improves Behavior Repertoire in Broilers , 2012, PloS one.

[148]  J. H. Smith,et al.  Relationships among mineral balance in the diet, early growth manipulation, and incidence of tibial dyschondroplasia in different strains of meat type chickens. , 1989, Poultry science.

[149]  David Sainsbury,et al.  Poultry Health and Management: Chickens, Turkeys, Ducks, Geese and Quail , 1992 .

[150]  C. Arnould,et al.  In Ovo Olfactory Experience Influences Post‐hatch Feeding Behaviour in Young Chickens , 2010 .

[151]  R. Tengerdy,et al.  Effect of vitamin E and A on humoral immunity and phagocytosis in E. coli infected chicken. , 1977, Poultry science.

[152]  Patrice Perny,et al.  Overall assessment of animal welfare: strategy adopted in Welfare Quality® , 2009, Animal Welfare.

[153]  Ç. Yenisey,et al.  Brooding temperatures for chicks acclimated to heat during incubation: effects on post-hatch intestinal development and body weight under heat stress , 2010, British poultry science.

[154]  W. Guenter,et al.  Abdominal fat deposition and sudden death syndrome in broilers: the effects of restricted intake, early life caloric (fat) restriction, and calorie: protein ratio. , 1984, Poultry science.

[155]  M. Choct,et al.  Nutrient utilization and functionality of the anterior digestive tract caused by intermittent feeding and inclusion of whole wheat in diets for broiler chickens. , 2010, Poultry science.

[156]  L. Keeling,et al.  Resting or hiding? Why broiler chickens stay near walls and how density affects this , 2010 .

[157]  I. Halle,et al.  Influence of Temperature Manipulation during the Last 4 Days of Incubation on Hatching Results, Post-Hatching Performance and Adaptability to Warm Growing Conditions in Broiler Chickens , 2011 .

[158]  Christopher M. Wathes,et al.  Light, Vision and the Welfare of Poultry , 2003, Animal Welfare.

[159]  R. Else,et al.  High litter moisture alone is sufficient to cause footpad dermatitis in growing turkeys , 2007, British poultry science.

[160]  P. Ferket,et al.  Dietary calcium and phosphorus effects on broiler performance and the incidence of sudden death syndrome mortality. , 1995, Poultry science.

[161]  B. L. Nielsen,et al.  Splitting the scotoperiod: effects on feeding behaviour, intestinal fill and digestive transit time in broiler chickens , 2011, British poultry science.

[162]  M. Y. Shim,et al.  Effects of incubation temperature on the bone development of broilers. , 2011, Poultry science.

[163]  A. Idowu,et al.  Growth response, nutrient and mineral retention, bone mineralisation and walking ability of broiler chickens fed with dietary inclusion of various unconventional mineral sources. , 2011, Journal of animal physiology and animal nutrition.

[164]  Z. Niu,et al.  Effects of different levels of vitamin E on growth performance and immune responses of broilers under heat stress. , 2009, Poultry science.

[165]  R. Cooper,et al.  The impact of L-NAME and L-arginine chronic toxicity induced lesions on ascites--pulmonary hypertension syndrome development in broiler chickens. , 2011, Collegium antropologicum.

[166]  I. H. Çerçi̇,et al.  Impact of stocking density and feeding regimen on broilers: performance, carcass traits and bone mineralisation , 2011 .

[167]  R. C. Newberry,et al.  Use of visual cover by domestic fowl: a Venetian blind effect? , 1997, Animal Behaviour.

[168]  C. J. Mirocha,et al.  Fusarium-Induced Osteochondrosis (Tibial Dyschondroplasia) in Chickens , 1982, Veterinary pathology.

[169]  C. Arnould,et al.  Emotions and cognition: a new approach to animal welfare , 2006, Animal Welfare.

[170]  J. Hess,et al.  Effect of light intensity on live performance and processing characteristics of broilers. , 2008, Poultry science.

[171]  Trever G. Crowe,et al.  Effect of light intensity on broiler behaviour and diurnal rhythms , 2012 .

[172]  R. Fleming.  Nutritional factors affecting poultry bone health , 2008, Proceedings of the Nutrition Society.

[173]  J. Malmkvist,et al.  Proportion of insoluble fibre in the diet affects behaviour and hunger in broiler breeders growing at similar rates. , 2011, Animal : an international journal of animal bioscience.

[174]  C. Savory.  The relationship between food and water intake and the effects of water restriction on laying brown leghorn hens , 1978 .

[175]  I. Estevez.  Density allowances for broilers: where to set the limits? , 2007, Poultry science.

[176]  M. Elferink.  Genetic variation in the chicken genome: insights in selection , 2011 .

[177]  J. Garner,et al.  Dustbathing by broiler chickens: a comparison of preference for four different substrates , 2004 .

[178]  A. Butterworth,et al.  Dehydration and Lameness in a Broiler Flock , 2002, Animal Welfare.

[179]  W. Bessei,et al.  Effect of locomotor activity on bone development and leg disorders in broilers , 1998 .

[180]  Cécile Cornou,et al.  Automatic detection of deviations in activity levels in groups of broiler chickens – A pilot study , 2011 .

[181]  H. M. Edwards,et al.  The role of calcium and phosphorus in the etiology of tibial dyschondroplasia in young chicks. , 1983, The Journal of nutrition.

[182]  Irenilza de Alencar Nääs,et al.  Estimativa de bem-estar de frango de corte em função da concentração de amônia e grau de luminosidade no galpão de produção , 2007 .

[183]  Jean-Marie Aerts,et al.  Modelling the dynamic activity of broiler chickens in response to step-wise changes in light intensity , 2006 .

[184]  B. L. Nielsen,et al.  Breast blisters in groups of slow-growing broilers in relation to strain and the availability and use of perches , 2004, British poultry science.

[185]  Y. Zhang,et al.  Fine-mapping of quantitative trait loci for body weight and bone traits and positional cloning of the RB1 gene in chicken. , 2011, Journal of animal breeding and genetics = Zeitschrift fur Tierzuchtung und Zuchtungsbiologie.

[186]  M. R. Reddy,et al.  Interaction between dietary calcium and non-phytate phosphorus levels on growth, bone mineralization and mineral excretion in commercial broilers , 2006 .

[187]  G. Sönmez,et al.  Effects of different management factors on broiler performance and incidence of tibial dyschondroplasia , 2005, British poultry science.

[188]  K. Reiter.  Behaviour and welfare of broiler chicken , 2006 .

[189]  J. Berk.  [Effect of litter type on prevalence and severity of pododermatitis in male broilers]. , 2009, Berliner und Munchener tierarztliche Wochenschrift.

[190]  P. Koene,et al.  Eating behaviour, and preprandial and postprandial correlations in male broiler and layer chickens , 2003, British poultry science.

[191]  Inma Estevez,et al.  Analysis of the movement and use of space of animals in confinement: the effect of sampling effort , 2006 .

[192]  I. Duncan,et al.  Feeding motivation on the incidence of floor eggs and extraneously calcified eggs laid by broiler breeder hens , 2011, British poultry science.

[193]  D. Bastianelli,et al.  Genetic parameters of digestibility of wheat- or corn-based diets in chickens , 2010 .

[194]  J. Faure,et al.  Effects of increasing environmental complexity on the physical activity of broiler chickens , 2002 .

[195]  R.Bryan Jones,et al.  Fear and adaptability in poultry: insights, implications and imperatives , 1996 .

[196]  P. Lewis,et al.  Photoperiodic responses of broilers. II. Ocular development , 2009, British poultry science.

[197]  Z. Song,et al.  Stocking density affects the growth performance of broilers in a sex-dependent fashion. , 2011, Poultry science.

[198]  C. Whitehead,et al.  Effectiveness of dietary 25- and 1-hydroxycholecalciferol in combating tibial dyschondroplasia in broiler chickens. , 1996, British poultry science.

[199]  D. Broom,et al.  Number of flocks on the same litter and carcase condemnations due to cellulitis, arthritis and contact foot-pad dermatitis in broilers , 2010, British poultry science.

[200]  I. Estevez,et al.  Effects of density on perching behavior of broiler chickens. , 2001, Applied animal behaviour science.

[201]  Sacit F. Bilgili,et al.  The Effects of Photoperiod Length, Light Intensity, and Feed Energy on Growth Responses and Meat Yield of Broilers , 2006 .

[202]  Faure,et al.  Early locomotor behaviour in genetic stocks of chickens with different growth rates. , 2000, Applied animal behaviour science.

[203]  J. D. Lund,et al.  Influence of light-dark schedules and stocking density on behaviour, risk of leg problems and occurrence of chronic fear in broilers , 2002, British poultry science.

[204]  Z. Nikousefat,et al.  Effect of vitamin E in heat-stressed poultry , 2011 .

[205]  S. Leeson,et al.  Effect of arginine:lysine ratios and source of methionine on growth and body protein accretion in acutely and chronically heat-stressed broilers. , 2006, Poultry science.

[206]  N. Stickland,et al.  Muscle specific differences in the regulation of myogenic differentiation in chickens genetically selected for divergent growth rates , 2011, Differentiation; research in biological diversity.

[207]  D. Berckmans,et al.  Application of a fully automatic analysis tool to assess the activity of broiler chickens with different gait scores , 2010 .

[208]  M. T. Prieto,et al.  Effects of auditory and physical enrichment on 3 measurements of fear and stress (tonic immobility duration, heterophil to lymphocyte ratio, and fluctuating asymmetry) in several breeds of layer chicks. , 2011, Poultry science.

[209]  R. Wideman,et al.  Methylglyoxal and pulmonary hypertension in broiler chickens. , 2011, Poultry science.

[210]  Ian Paul McCarthy,et al.  The relationship between physical activity and leg health in the broiler chicken , 2010, British poultry science.

[211]  E. Russek-Cohen,et al.  Effect of Perches and Stocking Density on Tibial Dyschondroplasia and Bone Mineralization as Measured by Bone Ash in Broiler Chickens , 2003 .

[212]  J. Garner,et al.  Effect of sand and wood-shavings bedding on the behavior of broiler chickens. , 2005, Poultry science.

[213]  L. Douglass,et al.  Using artificial cover to reduce aggression and disturbances in domestic fowl , 2002 .

[214]  J. Moyle,et al.  Mating behavior in commercial broiler breeders: Female effects , 2010 .

[215]  F. Gao,et al.  Effects of dietary glutamine and gamma-aminobutyric acid on performance, carcass characteristics and serum parameters in broilers under circular heat stress , 2011 .

[216]  F. Pol,et al.  Risk factors for foot-pad dermatitis in chicken and turkey broilers in France. , 2002, Preventive veterinary medicine.

[217]  B. Danuser,et al.  Respiratory symptoms in European animal farmers. , 2001, The European respiratory journal.

[218]  R. C. Newberry,et al.  Broiler chickens: a tolerant social system? , 1997 .

[219]  A. Omar,et al.  Physiological responses of 3 chicken breeds to acute heat stress. , 2011, Poultry science.

[220]  W. Bessei,et al.  Effect of whole wheat and feed pellets distribution in the litter on broilers' activity and performance. , 2011 .

[221]  J. Thaxton,et al.  Interactive effects of ammonia and light intensity on hematochemical variables in broiler chickens. , 2008, Poultry science.

[222]  Olsson,et al.  Night-time roosting in laying hens and the effect of thwarting access to perches. , 2000, Applied animal behaviour science.

[223]  R. Freire,et al.  Minor beak trimming in chickens leads to loss of mechanoreception and magnetoreception. , 2011, Journal of animal science.

[224]  F. Proudfoot,et al.  EFFECT OF DIETARY CATION-ANION BALANCE AND CALCIUM CONTENT ON GENERAL PERFORMANCE AND INCIDENCE OF LEG ABNORMALITIES OF BROILER CHICKENS , 1987 .

[225]  T G Crowe,et al.  Effect of light intensity on broiler production, processing characteristics, and welfare. , 2010, Poultry science.

[226]  M. Toghyani,et al.  Assessment of growth performance, immune responses, serum metabolites, and prevalence of leg weakness in broiler chicks submitted to early-age water restriction , 2011, Tropical Animal Health and Production.

[227]  J. Buyse,et al.  Effects of dietary supplementation of methionine and its hydroxy analog DL-2-hydroxy-4-methylthiobutanoic acid on growth performance, plasma hormone levels, and the redox status of broiler chickens exposed to high temperatures. , 2011, Poultry science.

[228]  H. Bovenhuis,et al.  Selection strategies for body weight and reduced ascites susceptibility in broilers. , 2005, Poultry science.

[229]  W. Stricklin,et al.  Use of horizontal and angled perches by broiler chickens , 2000 .

[230]  B. Kemp,et al.  High eggshell temperatures during incubation decrease growth performance and increase the incidence of ascites in broiler chickens. , 2011, Poultry science.

[231]  E. Decuypere,et al.  Comparison of bruises and mortality, stress parameters, and meat quality in manually and mechanically caught broilers. , 2005, Poultry science.

[232]  A. Gupta,et al.  Ascites syndrome in poultry: a review , 2011 .

[233]  L. Keeling,et al.  Using motivation to feed as a way to assess the importance of space for broiler chickens , 2011, Animal Behaviour.

[234]  F. Sirri,et al.  Foot dermatitis and productive traits in broiler chickens kept with different stocking densities, litter types and light regimen , 2007 .

[235]  W. Bessei,et al.  Effect of stocking density of broilers on temperature in the litter and at bird level. , 2000 .

[236]  A. Prasad,et al.  Role of dietary zinc in heat-stressed poultry: a review. , 2009, Poultry science.

[237]  F. Tuyttens,et al.  Stocking density effects on broiler welfare: identifying sensitive ranges for different indicators. , 2009, Poultry science.

[238]  J. Jarp,et al.  Factors associated with mortality in Norwegian broiler flocks. , 2002, Preventive veterinary medicine.

[239]  Christl A. Donnelly,et al.  Forced to crowd or choosing to cluster? Spatial distribution indicates social attraction in broiler chickens , 2006, Animal Behaviour.

[240]  I. D. Boer,et al.  Space needs of broilers , 2011, Animal Welfare.

[241]  V. Sandilands,et al.  Assessing leg health in chickens using a force plate and gait scoring: how many birds is enough? , 2011, Veterinary Record.

[242]  T. Yaqub,et al.  Single or combined effects of mannan-oligosaccharides and probiotic supplements on the total oxidants, total antioxidants, enzymatic antioxidants, liver enzymes, and serum trace minerals in cyclic heat-stressed broilers. , 2011, Poultry science.

[243]  S. Avendaño,et al.  The structure of feeding behavior in commercial broiler lines selected for different growth rates. , 2009, Poultry science.

[244]  J. B. Kjaer,et al.  Feeding activity in groups of newly hatched broiler chicks: effects of strain and hatching time. , 2010, Poultry science.

[245]  W. Verbeke,et al.  Economic impact of decreasing stocking densities in broiler production in Belgium. , 2011, Poultry science.

[246]  J. Palermo-neto,et al.  Heat stress impairs performance parameters, induces intestinal injury, and decreases macrophage activity in broiler chickens. , 2010, Poultry science.

[247]  R. Lacey,et al.  A Review of Literature Concerning Odors, Ammonia, and Dust from Broiler Production Facilities: 4. Remedial Management Practices , 2004 .