**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** STATEGICALLY-COATED MAGNETIC NANO-PARTICLES WILL BE USED TO REMOVE DEFECTIVE SPERMATOZOA FROM THE EJACULATE OF BULLS AND FIELD STUDIES WITH THE NANO-PURIFIED SEMEN WILL BE USED TODEMONSTRATED GREATER FERTILITY. LIVESTOCK FERTILITY IS CRITICAL TO THE PRODUCTION EFFICIENCY AND ECONOMIC SURVIVAL OF BEEF AND DAIRY CATTLE PRODUCERS. ARTIFICIAL INSEMINATION (AI) IS USED BY MORE PROGRESSIVE BEEF AND DAIRY PRODUCERS AND IS THE MOST EFFICIENT WAY TO IMPROVE GENETICS OF THEIR CATTLE. SEMEN EJACULATES OF ALL MAMMALS CONTAIN 3 SUBPOPULATIONS OF SPERMATOZOA. THE FIRST SUBPOPULATION CONTAINS SPERM THAT ARE FULLY COMPETENT TO FERTILIZE AN EGG AND AND CREATE A SUCCESSFUL PREGNANCY. THE SECOND SUBPOPULATION (COMPENSABLE SPERM) ARE DEAD OR IMMOTILE SPERM THAT DO NOT COMPETE WITH FERTILIZATION, WHILE THE THIRD POPULATION (UNCOMPENSABLE SPERM) COMPETES WITH FULLY COMPETENT SPERM, BUT DOES NOT RESULT IN PROPER EMBRYONIC DEVELOPMENT AND A SUCCESSFUL PREGNANCY. THUS, REMOVAL OF THE UNCOMPENSABLE SPERM FROM AN EJACULATE BEFORE DILUTION AND FREEZING IMPROVES THE FERTILITY OF THE SEMEN AND DECREASES THE NUMBER OF SPERM THAT NEED TO BE IN THE AI DOSE. THE OBJECTIVES OF THIS PROPOSAL ARE TO EVALUATE REPRODUCTIVE POTENTIAL OF NANO-PURIFIED SPERM FROM BULLS AND DEVELOP NEW BIOMARKER TARGETS FOR NANO-PURIFICATION TECHNIQUES TO FURTHER IMPROVE FERTILITY OF GENETICALLY SUPERIOR SIRES. THIS RESEARCH WILL INCREASE THE NUMBER OF AI DOSES THAT CAN BE OBTAINED FROM EACH EJACULATE AND IMPROVE THE FERTILITY OF AI FOR BEEF AND DAIRY PRODUCERS AND INCREASE OVERALL BEEF AND DAIRY PRODUCTIVITY. INFORMATION LEARNED FROM RESEARCH WILL ALSO CONTRIBUTE TO IMPROVING THE FERTILITY EXAM OF BULLS BY IDENTIFYING THE RELATIVE CONTRIBUTIONSSPECIFIC UNCOMPENSABLE OR SUBFERTILE SPERM HAVE ON FIELD FERTILITY.