** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** EGGS ARE AN AFFORDABLE, HIGH-QUALITY PROTEIN SOURCE PRODUCED BY THE COMMERCIAL LAYING HEN INDUSTRY. LIKE ALL SECTORS OF AGRICULTURE, THIS INDUSTRY FACES CHALLENGES SURROUNDING WAYS TO INCREASE FOOD PRODUCTION TO MEET THE NEEDS OF A GROWING GLOBAL POPULATION IN AN ENVIRONMENTALLY SUSTAINABLE AND ECONOMICALLY VIABLE MANNER. ONE WAY THE LAYING HEN INDUSTRY HAS TRIED TO MEET THIS CHALLENGE IS BY EXTENDING FLOCK PRODUCTION CYCLES TO INCREASE THE TOTAL NUMBER OF EGGS LAID PER HEN FROM ABOUT 320 AT 72 WEEKS OF AGE TO 500 AT 100 WEEKS OF AGE. THESE LONG-LIFE LAYERS ALLOW FOR DECREASED CARBON FOOTPRINT AND INCREASED PROFITABILITY ON A PER EGG BASIS, SINCE THE 18-WEEK PERIOD WHEN THE BIRDS ARE RAISED PRIOR TO WHEN EGG PRODUCTION STARTS IS A SMALLER FRACTION OF THE FLOCK'S LIFE. LAYING HENS PRODUCE ABOUT ONE EGG EVERY 24 HOURS ONCE THEY REACH SEXUAL MATURITY, A PROCESS INVOLVING DAILY MOBILIZATION OF CALCIUM AND PHOSPHORUS STORES FROM BONE FOR USE IN EGGSHELL FORMATION. AS HENS GET OLDER, THEY BECOME LESS EFFICIENT AT USING THESE MINERALS FOR EGGSHELL FORMATION AND BONE REMODELING, LEADING TO OSTEOPOROSIS, INCREASED INCIDENCE OF BONE FRACTURES, KEEL DEFORMITIES, AND REDUCED EGG QUALITY FROM THINNING SHELLS. AS A RESULT, MANAGING HENS THROUGH AN EXTENDED PRODUCTION CYCLE LEADS TO CHALLENGES INVOLVING THE AFOREMENTIONED WELFARE AND ECONOMIC CONCERNS. OUR OVERALL HYPOTHESIS IS THAT THE DYNAMIC CHANGES THAT OCCUR DURING THE 24H EGG FORMATION CYCLE WILL CHANGE FROM THE ONSET OF EGG PRODUCTION, THROUGH THE PEAK EGG LAYING PERIOD, AND INTO EXTENDED PRODUCTION. THE HENS ARE EXPECTED TO BECOME LESS EFFICIENT AT ABSORBING AND UTILIZING CALCIUM AND PHOSPHORUS FOR BONE AND EGGSHELL FORMATION AS THEY AGE. WE FURTHER HYPOTHESIZE THAT DIETARY SUPPLEMENTATION WITH A MORE ACTIVE FORM OF VITAMIN D3, ALPHA D3, WILL IMPROVE MINERAL UTILIZATION FOR BONE AND EGGSHELL FORMATION, ULTIMATELY ENHANCING ANIMAL WELFARE AND EGG QUALITY DURING EXTENDED PRODUCTION. THIS PROJECT WILL IDENTIFY KEY BIOLOGICAL SYSTEMS AND PROCESSES ASSOCIATED WITH LAYING HEN UTILIZATION OF CALCIUM AND PHOSPHORUS FOR EGGSHELL AND BONE MINERALIZATION. IT WILL FURTHER EVALUATE HOW THESE SYSTEMS AND PROCESSES CHANGE WITH AGE AND ARE INFLUENCED BY DIETARY SUPPLEMENTATION WITH A MORE BIOLOGICALLY ACTIVE FORM OF VITAMIN D3. THE MECHANISMS TO BE STUDIED ARE ASSOCIATED WITH ACTIONS OF HORMONES REGULATING MINERAL UTILIZATION BY IMPORTANT TISSUES THAT INCLUDE SHELL GLAND, KIDNEY, INTESTINE, AND LIVER. PARAMETERS ASSOCIATED WITH EGGSHELL QUALITY AND BONE HEALTH WILL ALSO BE EVALUATED. IN ADDITION, THE IMPACT OF FEEDING ALPHAD3 ON BIOLOGICAL PROCESSES, EGGSHELL PARAMETERS, AND BONE CHARACTERISTICS WILL BE DETERMINED. IT IS EXPECTED THAT IMPORTANT PROCESSES AND TISSUES ASSOCIATED WITH MINERAL UTILIZATION WILL BE IDENTIFIED, AND THESE PROCESSES WILL INVOLVE METABOLISM OF DIETARY VITAMIN D3, HORMONAL SIGNALING, AND MINERAL UPTAKE AND TRANSPORT. THE IMPACT OF AGE AND SOURCE OF DIETARY VITAMIN D3 WILL ALSO BE DETERMINED.,TOGETHER, RESULTS FROM THIS PROJECT WILL ELUCIDATE FUNDAMENTAL BIOLOGICAL PROCESSES REGULATING LAYING HEN CALCIUM AND PHOSPHORUS HOMEOSTASIS AT THE CELLULAR, TISSUE, AND WHOLE-BIRD LEVEL AND IDENTIFY NOVEL BIOMARKERS FOR IMPROVED EGGSHELL AND SKELETAL STRENGTH. FURTHER, THEY WILL REVEAL WHICH OF THE SYSTEMS CHANGE MOST SUBSTANTIALLY WITH AGE AND COULD CONTRIBUTE TO THE REDUCTION IN EFFICIENCY OF CALCIUM AND PHOSPHORUS UTILIZATION FOR BONE AND EGGSHELL FORMATION IN OLDER HENS, MAKING THEM KEY TARGETS FOR STRATEGIES TO IMPROVE BOTH EGGSHELL QUALITY AND HEN SKELETAL WELFARE DURING EXTENDED LAY. SUCCESSFUL DEVELOPMENT AND IMPLEMENTATION OF SUCH STRATEGIES WOULD SUBSTANTIALLY IMPROVE CONSUMER PERCEPTION OF THE LAYING HEN INDUSTRY AS WELL AS INCREASE THE NUMBER OF SALABLE EGGS RESULTING FROM EACH PRODUCTION CYCLE. BOTH OF THESE OUTCOMES WILL ALLOW FOR IMPROVED EFFICIENCY AND SUSTAINABILITY OF EGG PRODUCTION THAT WOULD BE PASSED ON TO THE CONSUMER IN THE FORM OF A REDUCED COST FOR POULTRY PRODUCTS.