** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** THE NORTHERN FOWL MITE (NFM) IS THE MOST PROBLEMATIC AND ECONOMICALLY COSTLY BLOOD-FEEDING ECTOPARASITE OF LAYING HENS IN THE U.S., RESULTING IN DECREASED WELFARE AND LOST EGG PRODUCTION IN MILLIONS OF EGG LAYING HENS. CURRENT METHODS TO COMBAT THIS ECTOPARASITE ARE LIMITED. THERE IS CONSIDERABLE INDIVIDUAL VARIATION AMONG LAYING HENS IN THEIR ABILITY TO RESIST NFM INFESTATION, WITH INFESTATIONS VARYING AMONG BIRDS OF THE SAME AGE, SEX, AND STRAIN. THEREFORE, IDENTIFYING INDIVIDUAL CHARACTERISTICS THAT CONFER RESISTANCE TO NFM AND THAT ARE HERITABLE HAS THE POTENTIAL TO GREATLY IMPROVE LAYING HEN WELFARE AND SUSTAINABILITY OF THE U.S. EGG INDUSTRY.THE OVERARCHING GOAL OF THIS PROJECT IS TO DEVELOP GENETIC AND GENOMIC STRATEGIES BASED ON INDIVIDUAL HEN CHARACTERISTICS THAT IMPROVE LAYING HEN RESILIENCE AND RESISTANCE TO NFM. THE SPECIFIC OBJECTIVES ARE TO IDENTIFY: 1) INDIVIDUAL BIRD CHARACTERISTICS ASSOCIATED WITH NFM RESISTANCE AND SUSCEPTIBILITY, AND INFESTATION EFFECTS ON HEN PRODUCTIVITY AND WELFARE; AND 2) THE GENOMIC BACKGROUND OF NOVEL TRAITS RELATED TO NFM RESISTANCE AND RESILIENCE AND INVESTIGATE THEIR GENOMIC PREDICTIVE PERFORMANCE. LAYING HENS WILL BE EXPERIMENTALLY INFESTED WITH NFM AND DATA PERTAINING TO HEN WELFARE, BEHAVIOR, INFLAMMATION, SKIN LESIONS AND FEATHER CONDITION WILL BE COLLECTED FROM 20 TO 40 WEEKS OF AGE TO IDENTIFY NOVEL TRAITS ASSOCIATED WITH RESILIENCE AND RESISTANCE TO NFM. THE IMPACTS OF NFM INFESTATION ON HEN PRODUCTIVITY AND EGG QUALITY WILL ALSO BE EXAMINED.THIS PROJECT ADDRESSES THE NIFA-AFRI ANIMAL WELL-BEING PROGRAM AREA PRIORITY OF ADVANCING OBJECTIVE MEASURES OF ANIMAL WELFARE AND SELECTION FOR ANIMAL ROBUSTNESS.