**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** PASTURED COW-CALF SYSTEMS ARE RESPONSIBLE FOR AN ESTIMATED 70% OF ALL GREENHOUSE GAS (GHG) EMISSIONS IN BEEF PRODUCTION, MAINLY IN THE FORM OF METHANE THROUGH ENTERIC FERMENTATION.WITH A NATIONAL GOAL TO REDUCE GHG EMISSIONS BY 50% BEFORE THE YEAR 2030, A HIGH VALUE HAS BEEN PUT ON GHG MITIGATION STRATEGIES FOR PREVIOUSLY UNDEREXPLORED AGRICULTURAL SECTORS. COW-CALF PRODUCTION IS RESPONSIBLE FOR GENERATING TREMENDOUS AMOUNTS OF METHANE AND IS ONE OF THESE UNDEREXPLORED AGRICULTURAL SECTORS. A CLEAR RELATIONSHIP BETWEEN PARASITE CONTROL AND IMPROVED ANIMAL PERFORMANCE HAS BEEN ESTABLISHED PREVIOUSLY BUT HOW IT RELATES TO GHG PRODUCTION REMAINS POORLY UNDERSTOOD, ESPECIALLY FOR COW-CALF PRODUCTION. THIS PROJECT WILL DEFINE HOW PARASITES ALTER GHG EMISSIONS IN COW-CALF SYSTEMS AND CORRELATE PARASITE LOAD WITH ANIMAL PERFORMANCE.TO CHARACTERIZE THIS IMPORTANT RELATIONSHIP, WE WILL MEASURE WEIGHT GAIN, STRESS BIOINDICATORS THROUGH BLOODWORK, AND GHG EMISSIONS THROUGH A SULFUR HEXAFLUORIDE SYSTEM IN COW-CALF PAIRS THAT HAVE BEEN ADMINISTERED ONE OF FOUR PARASITICIDAL TREATMENT REGIMES: 1) HORN FLY AND GUT NEMATODE CHEMICALCONTROL TREATMENT, 2) HORN FLY-ONLY CHEMICAL CONTROL TREATMENT, 3) GUT NEMATODE-ONLY CHEMICAL CONTROL TREATMENT, 4) NO CHEMICAL CONTROL TREATMENT. WEIGHT GAIN WILL BE MEASURED MONTHLY ALONG WITH COAT THICKNESS, BLOOD CHEMISTRY, AND SULFUR HEXAFLUORIDE CANNISTERS ATTACHED TO ANIMALS WILL BE COLLECTED DAILY AND MEASURED FOR METHANE AND SULFUR HEXAFLUORIDE CONCENTRATIONS. HORN FLIES WILL BE COUNTED ON ANIMAL SIDES USING DIGITAL PHOTOGRAPHY GUT NEMATODES WILL BE QUANTIFIED BY FECAL EGG COUNTS COLLECTED FROM ANIMALS.PARASITE PHENOLOGY WILL BE MEASURED IN A NUMBER OF WAYS. FIRST, ANIMAL BEHAVIORS SIGNIFYING HEAVY HORN FLY LOAD WILL BE MEASURED BY DEFENSIVE BEHAVIORS SUCH AS SIDE LICKS, TAIL FLICKS, HEAD THROWS, LEG STOMPS, AND BELLY KICKS. TO DETERMINE PHENOLOGY, IMMATURE HORN FLIES AND NEMATODES WILL BE SAMPLED WEEKLY FROM AT LEAST 20 FRESH MANURE PATS BY FLOATATION. HORN FLY LARVAE AND PUPAE ARE EASILY IDENTIFIED BY MORPHOLOGICAL MARKERS. NEMATODE IMMATURES WILL BE IDENTIFIED MOLECULARLY TO SPECIES USING STANDARD MOLECULAR BARCODING TECHNIQUES.THE ULTIMATE GOAL OF THIS PROJECT IS TO BETTER UNDERSTAND THE ROLE PARASITES PLAY IN METHANE PRODUCTION IN COW-CALF PRODUCTION. BY UNDERSTANDING THIS HOST-PARASITE RELATIONSHIP BETTER, PRODUCERS WILL ULTIMATELY GAIN SOLUTIONS TO METHANE REDUCTION THAT WILL FUTURE-PROOF THEM FROM CARBON TAXES LEVIED AGAINST AGRICULTURAL PRODUCTION AND SIMULTANEOUSLY IMPROVE PROFITABILITY BY RAISINGHEALTHIER ANIMALS (AS A RESULT OF LOW PARASITE LOAD). AN OVERALL REDUCTION IN METHANE PRODUCTION IN COW-CALF SYSTEMS CONTRIBUTES TO THE GOAL OF OVERALL CARBON REDUCTION BY THE UNITED STATES BY 2030.