Effects Of Keel Fracture On Behavior, Welfare, Production Performance And Bone Quality Of Laying Hens

In modern intensive laying hen production systems,due to the increasing attention to the welfare of laying hens,European Union have banned the traditional cage-raised hens from 2012.Therefore,the furnished cage and non-cage systems have become main raised-model of laying hens.Unfortunately,with the transfer of laying hens from traditional cages to furnished cages and noncage systems,laying hens still face many welfare and health problems,of which the keel damage(keel fracture and deviation)is among the most prevalent.The incidence of keel damage varies among different laying systems,ages and breeds.Therefore,the aim of this study is to assess the relationships between keel fracture and behavior,welfare,keel bone quality and orexin system of Lohmann white laying hens in individually furnished cage,and supply the existing knowledge base for the effect of keel fracture on laying hens.Experiment 1: To investigate the effect of keel fracture on behavior,welfare,production performance and egg quality of laying hens,a total of 90 healthy Lohmann white laying hens,17 weeks of age at the onset of the experiment,were used in this study and housed in individually furnished cage.The behaviors were observed for 2 consecutive days at 22,27,32,37 and 42 weeks(per 5 weeks)of age,and record the total numbers of egg production,dirty egg,broken egg and feed intake of keel fractured and normal laying hens before the next palpation,respectively.Following each behavioral observation,the hens of keel fracture and normal were marked based on whether keel fracture occurred by palpation.After each palpation,10 laying hens of keel fracture and normal were randomly selected,respectively,as focal animals to assess their welfare and determinate egg quality.The results showed that the incidence of keel fracture was increased with the increase of age of laying hens.Compared to normal laying hens,the sitting and standing behavior were significantly increased(p < 0.05),feeding,walking,perching and jumping behavior were significantly decreased of keel fractured laying hens(p < 0.05).There were no significantly changes in drinking,preening,comforting,cage pecking and nesting behavior between keel fractured and normal laying hens(p > 0.05).During experiment period from 27 to 42 weeks of age,the egg production rate,body weight,eggshell strength,thickness and weight were decreased(p < 0.05),broken-egg rate and duration of tonic immobility were increased for laying hens of keel fracture compared to normal hens(p < 0.05).Keel fracture had no significant effect on the dirty-egg rate,egg shape index,protein height,Haugh units,feather quality,claw toe and foot pad health(p > 0.05).Experiment 2: To investigate the effects of keel fracture on keel bone quantity,stress response and orexin system of laying hens.A total of 90 healthy Lohmann white laying hens,17 weeks of age at the onset of the experiment,were used in this study and housed in individually furnished cage.The hens of keel fracture and normal were recorded based on whether keel fracture occurred at 22,27,32,37 and 42 weeks(per 5 weeks)of age by palpation,respectively.Following the palpation at 42 weeks of age,we randomly selected 10 laying hens from keel fractured and normal groups,respectively,as focal animals to collect serum,brain,liver,bone and muscle tissues,and then determinate the activity of bone metabolism indexes,the content concentration of 30 mineral elements and the expression of heat shock proteins(Hsps),inflammatory factors,orexin and orexin receptor genes.The results showed that keel fracture can increase the content of osteocalcin(OC)and the activity of alkaline phosphatase(ALP)in serum and keel bone,the content of corticosterone in serum,and the activity of tartaric acid resistant phosphatase(TRACP)in keel bone(p < 0.05).Keel fracture also caused significant increase in the concentration of Li,B,K,Cu,As,Se,Sn,Hg and Pb elements(p < 0.05),and decrease in that of Na,P and Ca elements in keel bones(p < 0.05).The m RNA expression levels of Hsp60,Hsp70 and Hsp90 and protein levels of Hsp70 and Hsp90 were markedly increased in brain and liver tissues of keel fractured laying hens compared with that of normal hens(p < 0.05).There was no difference in the m RNA expression of i NOS in liver and TNF-α in muscle between keel fractured and normal laying hens(p > 0.05).The expression levels of other inflammatory factors(TNF-α,NF-κBp65,i NOS,PTGEs,COX-2,IL-1β)in brain,liver and muscle tissues of keel fractured hens were significantly higher than that of normal laying hens(p < 0.05).The protein expression levels of i NOS and COX-2 in liver,NF-κBp65,i NOS and COX-2 in brain of keel fractured laying hens were markedly higher than that of normal laying hens(p < 0.05).Otherwise,compared to normal laying hens,the expression levels of orexin and orexin receptors(ORX,ORXR1,ORXR2)m RNA in brain,liver and muscle of keel fractured laying hens were significantly increased(p < 0.05).Therefore,keel fracture could cause stress and inflammatory responses to laying hens,alter keel bone quality and inhibit the activity of orexin system.In conclusion,keel fracture may cause pain and fear for hens,lead to the increase in sitting and standing and decrease in feeding and activity behaviors,and reduced production performance and external egg quality.In addition,keel fracture also altered the activity of osteoblasts and osteoclasts,and the concentration of mineral elements,induced stress and inflammation responses,and inhibited the expression of orexin and orexin receptor genes.