Genome-wide Association Study Of Heat Stress’s Physiological Indicators In Chinese Holstein Population

Heat stress has a series of unfavourable effects on high producing lactating Holstein cow,which are associated with physiological changes including increased core body temperature,respiration rates,sweating,and endocrine system changes.Heat stress also cause significant declines in feed intake,milk production,fertility,and health problems.Simply counting only milk production declining heavy economic losses could be found in dairy industry.With the concept of balanced breeding,it’s necessary to improve heat tolerance in dairy cattle and will breed better adapted dairy herds to future climates.For conventional breeding,it is crucial to understand the population genetic parameters of the target traits first,then association study can be implemented to screen genetic markers which may be used in marker-assisted selection.Therefore,in this study,we targeted on heat stress physiological indicators: rectal temperature(RT),respiratory score and drooling score for dairy cows during heat stress.The main contents and results of our research are as follows:1.The data included rectal temperature,respiratory score and drooling score records from 12,541 lactating Holstein cows in Beijing area.A multiple-trait animal model was used to evaluate RT,respiratory score and drooling score,including estimating variances component,genetic parameters,and predicting breeding values.We also analysed the genetic trends and genetic correlation among RT respiratory score and drooling score.Results showed the estimated heritability of heat stress physiological indicators were 0.062-0.117,which is low and moderate,while the estimated repeatability were 0.657-0.773 as well as genetic correlation were 0.662-0.843 which is moderate and high.The three physiological indicators would be a recommended quantified indicator for heat stress response for dairy cattle.2.Though there is no directly selection for the three physiological indicators in dairy cows,the trends of physiological indicators EBVs in Beijing area of dairy cows born from 1990 to 2017 were increasing.It suggests that the breeding system targeting on genetics used in hot environment should pay attention to indicators responsed to heat stress and lay the foundation of differential breeding strategy to decrease the losses cause by heat stress.3.The genome-wide association study(GWAS)using the software Farm CPU was carried out on 2,598 Holstein cows with RT respiratory score and drooling score EBVs as phenotype.Results showed that fifteen SNPs were significant at genomic level(α=0.5).These SNPs were located in twelve different chromosomes and 19 genes were found near to those SNPs(within 300kb).The function of CLCX13、SLBP and PRKCE are related to immunity reproduction and lipid metabolism respectively.Those genes could be candidate genes of heat stressThis research targeted on directly indicators of physicological response to heat stress in dairy cattle.For the first time,we divided the genetic parameters of respiratory score and drooling score and implemented GWAS to detect genetic markers associated to related to response to heat stress in Chinese Holstein population.Therefore,our research provide theoretical parameters to establish a breeding scheme to improve heat tolerance in dairy through genetic selection.