Physiological And Multi-tissue Transcriptional Regulatory Mechanisms Underlie Cold Adaptation In Chickens

Cold stress negatively impacts the production performance,health and welfare of domesticated animals,inducing great economic losses.So it is important to improve the cold tolerance of animals.The aims of the present study were to examine the feasibility to simultaneously improve the cold tolerance and production performance of chickens by crossbreeding,and were to explore the physiological and multi-tissue transcriptional regulatory mechanisms underlying cold tolerance.The Bashang Long-tail(BS),a Chinese indigenous chicken breed,originated from the Bashang region in Hebei province,where the average altitude and the annual mean temperature are 1418 m and 1.9 ℃,respectively.The Rhode Island Red(RIR),a famous dual-purpose breed characterized by hardiness and good performance,is originally developed in Massachusetts and Rhode Island,USA.BS,RIR,and their reciprocal crossbreds(RIR males × BS females,RMBF;RIR females × BS males,RFBM)were used in the present study.The four groups of birds were reared in normal temperature and natural cold environments(Warm vs.Cold)from 19-39 weeks of age.In the warm environment,the mean air temperature was:15-25 ℃ during 19-25 weeks,10-15 ℃ during 26-39 weeks.In the cold environment,the mean air temperature was:10-27 ℃ during 19-25 weeks,0-10 ℃ during 26-29 weeks,-5 to 0 ℃ during 30-35 weeks,and-17.5 to-5 ℃ during 36-39 weeks.In the warm environment,the egg production performance of RIR was greater than RMBF and RFBM,which were greater than BS.In the cold environment,the egg production performance of RIR was lower than BS,which was lower than RMBF and RFBM.Moreover,when the mean air temperature dropped below 0 ℃ in the cold environment,the feed intake and body weight of RIR were dropped drastically,while those of BS were kept increase;those of the crossbreds were dropped,but less severe than RIR.These data indicated that the cold tolerance of BS was greater than RIR,and the cold tolerance and the production performance of the crossbreds were improved.In the cold environment,animals must increase heat production to maintain a constant body temperature,a process depends on hormonal regulation.We analyzed the serum biochemical parameters and cloacal temperature of the chickens.In the cold environment,the cloacal temperature of BS was dropped by 0.28 ℃,and that of crossbreds was dropped slightly,while that of RIR was kept constant.At 37 and 39 weeks of age,the cloacal temperature of BS reared in the cold environment was lower than that of BS reared in the warm environment,while the cloacal temperature of RIR,RMBF and RFBM reared in the cold envieornment were not different from the corresponding birds reared in the warm environment.A lower body temperature reduced heat losses,helping animals to acclimate to cold.BS and the crossbreds had higher serum GLU,T3,T4,FSH and LH levels than RIR after 35 weeks of age in the cold environment;it may be the reason for the greater cold tolerance and egg production performance of BS and the crossbreds.Hypothalamus-pituitary-thyroid axis and hypothalamus-pituitary-ovary axis regulate the metabolism and reproduction,respectively,in animals.We profiled the transcriptomes of the hypothalamus,pituitary,thyroid gland and ovary of BS and RIR,and analyzed transcriptional differences between breeds and transcriptional plasticity induced by temperature changes.The results showed that the corresponding tissues of BS and RIR were different at certain biological processes,indicating genetic heterogeneity which contribute to different cold tolerances;the transcriptional plasticity of corresponding tissues of BS and RIR were also different,suggesting different cold acclimation mechanisms.An alternative splicing event of TPO(encoding thyroid peroxidase)was found in thyroid tissue,the usage of exon 4 and 5 in the cold environment were different from that in the warm environment.We also constructed a multitissue weighted gene co-expression network using the transcriptome data of hypothalamus,pituitary,thyroid gland and ovary.19 gene modules were identified and 567 significant differentially expressed genes were found in all of the gene modules.The present study provide valuable information for future studies to disentangle chicken cold-tolerance mechanisms.