AS WE MOVE TOWARD THE NEXT COUPLE OF DECADES, THE WORLD'S AGRICULTURE WILL FACE ONE OF THE GREATEST CHALLENGES OF ALL TIME: TO PRODUCE ENOUGH FOOD TO FEED THE 9 BILLION PEOPLE THE EARTH WILL HOLD BY 2050. WITHOUT QUESTION, THIS WILL DEMAND THE CONCERTED EFFORTS OF PRODUCERS, RESEARCHERS, AND POLICYMAKERS TO PROVIDE THE EXPERIENCE, TECHNOLOGY, AND LEGAL FRAMEWORK NECESSARY TO ACCOMPLISH SUCH A DIFFICULT ENDEAVOR. AMONG THE DIFFERENT SOURCES OF ANIMAL PROTEIN, BEEF IS THE MOST NUTRIENT DENSE ON A PER CALORIE BASIS, SUPPLYING SEVERAL OF THE ESSENTIAL VITAMINS AND MINERALS WITH A RELATIVELY LOW CALORIC INTAKE PER SERVING.RUMINANTS SUCH AS CATTLE, SHEEP, AND GOATS HAVE A UNIQUE ADVANTAGE OVER NON-RUMINANTS IN TERMS OF NUTRITIONAL PHYSIOLOGY, BECAUSE THEY CARRY MICROORGANISMS IN THEIR GASTROINTESTINAL TRACT (GIT) THAT HOLD THE KEY TO THE DIGESTION OF FIBER. FIBER IS PRESENT IN FORAGES IN THE FORM OF CELLULOSE AND IS THE MOST ABUNDANT COMPLEX CARBOHYDRATE ON EARTH. BY HARBORING MICROORGANISMS IN THEIR GIT, RUMINANTS CAN TAKE ADVANTAGE OF FIBER DIGESTION BY CREATING A SYMBIOTIC RELATIONSHIP BETWEEN THE MICROBES AND THE RUMINANT HOST. THE MICROBES DIGEST THE FIBER AND PRODUCE BY-PRODUCTS KNOWN AS VOLATILE FATTY ACIDS, WHICH ARE IN TURN USED BY THE RUMINANT ANIMAL AS AN ENERGY SOURCE. IN RETURN, THE RUMINANT HOST PROVIDES A GOOD ENVIRONMENT FOR THE MICROORGANISMS AND PLENTY OF FEED TO SUSTAIN THEIR GROWTH. FOR THIS REASON, CATTLE, SHEEP, AND GOATS CAN THRIVE IN ENVIRONMENTS WHERE NO OTHER TYPE OF PRODUCTION SYSTEM CAN TAKE PLACE.NON-RUMINANTS, SUCH AS POULTRY AND SWINE, DO NOT HAVE THE ABILITY TO DIGEST FIBER AND RELY ON THE USE OF GRAIN AND PROTEIN SUPPLEMENTS TO ACHIEVE HIGH PRODUCTION LEVELS, COMPETING DIRECTLY WITH HUMANS FOR THE TYPE OF FEED USED (I.E., PLANT PROTEINS AND CEREAL GRAINS). THUS, RUMINANTS GRAZING IN AREAS WHERE NO CROPS CAN BE GROWN AND NO OTHER LIVESTOCK SPECIES CAN SURVIVE REPRESENT AN EXCELLENT OPPORTUNITY TO MAXIMIZE LAND USE, AND PROVIDE NUTRIENTRECYCLING IN THE FORM OF MANURE.AROUND THE WORLD, THE INITIAL PHASES OF THE BEEF PRODUCTION CYCLE (COW/CALF AND STOCKING SEGMENTS) ARE ALMOST ENTIRELY RELIANT ON THE USE OF FORAGES OR FIBROUS BY-PRODUCTS, AND THIS OFTEN TAKES PLACE ON LAND WHERE NO OTHER PRODUCTION SYSTEM CAN THRIVE. IN PARTICULAR, THE COW/CALF SEGMENT IN FLORIDA TAKES PLACE MOSTLY UNDER NATIVE VEGETATION AND RANGE CONDITIONS, WHICH PROVIDE WILDLIFE HABITAT FOR ENDANGERED AND NON-ENDANGERED SPECIES. THIS CONTRIBUTION OF BEEF CATTLE SYSTEMS IN THE FORM OF ECOSYSTEM SERVICES IS OFTEN OVERLOOKED. ADDITIONALLY, BEEF AND DAIRY CATTLE ARE PARTICULARLY EFFICIENT AT RECYCLING BY-PRODUCTS OF AGRICULTURE INDUSTRIES THAT ARE NOT SUITABLE FOR CONSUMPTION BY OTHER LIVESTOCK SPECIES. EXAMPLES INCLUDE THE USE OF CITRUS BY-PRODUCTS, DISTILLERS GRAINS (BY-PRODUCT FROM ETHANOL), AND CORN GLUTEN FEED (RESIDUE FROM WET MILLING OF CORN TO PRODUCE HIGH FRUCTOSE CORN SYRUP).UNFORTUNATELY, THIS ADVANTAGE BY RUMINANTS IN TERMS OF THEIR ABILITY TO DIGEST FIBER COMES AT A COST. THE PRODUCTION OF GREENHOUSE GASES SUCH AS CARBON DIOXIDE AND METHANE IS A RESULT OF THE ENTERIC FERMENTATION OF FEEDSTUFFS, AND THOSE GREENHOUSE GASES ARE RELEASED BY CATTLE AS A NECESSARY BYPRODUCT OF THEIR FERMENTATION OF FIBROUS FEEDS. THE "GREENHOUSE EFFECT" OF CERTAIN GASES REFERS TO THEIR ABILITY TO "TRAP" THE HEAT THAT IS GENERATED WHEN THE SUN RADIATION BOUNCES BACK AFTER HITTING THE EARTH'S SURFACE. THAT RADIATION CANNOT ESCAPE, AND THUS INCREASES THE ATMOSPHERIC TEMPERATURE, AFFECTING BIOLOGICAL PROCESSES IN DIVERSE MANNERS. THOSE GASES WITH SUCH CAPACITY TO RETAIN HEAT ARE CALLED GREENHOUSE GASES (GHG), AND THE THREE MOST COMMON GASES ARE CARBON DIOXIDE, METHANE, AND NITROUS OXIDE.THE ABILITY TO PRODUCE METHANE, THE MAIN CONTRIBUTOR OF THE GHG EMITTED BY CATTLE, IS MUCH GREATER IN ANIMALS CONSUMING FORAGE THAN THOSE CONSUMING A HIGH-GRAIN DIET. THUS, SEGMENTS OF BEEF PRODUCTION CHAIN THAT INVOLVE THE USE OF FORAGES AS THE MAIN RESOURCEARE GREATER CONTRIBUTORS IN TERMS OF GHG EMISSIONS. IN THE SOUTHEASTERN UNITED STATES, WHERE APPROXIMATELY 1/3 OF U.S. COWHERD RESIDES, FORAGES ARE THE MAIN FEED RESOURCE USED IN COW/CALF AND STOCKER PRODUCTION SYSTEMS. DESPITE THE SIGNIFICANCE OF THE SE UNITED STATES IN TERMS OF BEEF CATTLE NUMBERS, VERY LITTLE RESEARCH EFFORTS HAVE BEEN DEVOTED TO MITIGATE METHANE EMISSIONS IN FORAGE-BASED SYSTEMS.THE USE OF DIETS WITH HIGH CONCENTRATIONS OF SULFATE OR NITRATE CAN BE ALTERNATIVES TO DECREASE METHANE EMISSIONS AS IT HAS BEEN EVIDENCED IN SOME PREVIOUS STUDIES, SOME OF THOSE CONDUCTED IN OUR LABORATORY. BOTH NITRATE AND SULFATE ARE CHEMICAL ENTITIES THAT CAN OUTCOMPETE THE PROCESS THAT LEADS TO THE FORMATION OF METHANE, IN A CHEMICAL PHENOMENON CALLED REDUCTION. HOWEVER, EXCESS SULFUR IN THE DIETS CAN LEAD TO POOR ABSORPTION OF SOME OF THE MINERALS THAT ARE ESSENTIAL TO MAINTAIN CATTLE HEALTH AND REPRODUCTIVE ABILITY. IF CATTLE WERE ABLE TO RECEIVE A DIET HIGH IN SULFATES, AND AT THE SAME TIME MITIGATE THE EFFECTS THAT HIGH-SULFUR HAS ON MINERAL AVAILABILITY, THE USE OF HIGH SULFUR DIETS COULD BE AN ALTERNATIVE TO MITIGATE METHANE EMISSIONS. FORTUNATELY, SOME FORAGES GROWN IN THE SOUTHEASTERN U.S. CAN BE QUITE HIGH IN SULFUR, NATURALLY PROVIDING AN ALTERNATIVE TO DECREASE METHANE EMISSIONS. OUR LABORATORY HAS INVESTIGATED THE EFFECTS OF BISMUTH SUBSALICYLATE AS A FEED ADDITIVE TO BIND EXCESS DIETARY SULFUR AND MITIGATE THE NEGATIVE EFFECTS ON CATTLE, OBTAINING SOME PROMISING IN VITRO RESULTS. IN ADDITION, THE SAME IN VITRO RESULTS WERE USED TO TEST THE POTENTIAL OF NITRATES TO MITIGATE ENTERIC METHANE EMISSIONS, WHILE PROVIDING A SOURCE OF PROTEIN TO THE ANIMAL. THIS IS POSSIBLE BECAUSE NITRATE CAN BE USED BY THE RUMINAL MICROORGANISMS TO SYNTHESIZE PROTEIN THAT IN TURN IS USED BY THE RUMINANT TO MEET THEIR GROWTH AND MAINTENANCE NEEDS. HOWEVER, THE EFFECTS OF NITRATES AND BISMUTH SUBSALICYLATE COMBINED HAS NEVER BEEN STUDIED IN VIVO IN BEEF CATTLE.THUS, THE SPECIFIC OBJECTIVES OF THIS STUDY ARE:TO DETERMINE THE EFFECTS OF BSS IN COMBINATION WITH NITRATE ON IN VIVO RUMINAL FERMENTATION, METABOLISM, MICROBIAL ECOSYSTEM, AND ENTERIC CH4 PRODUCTION WHEN FEEDING A LOW-QUALITY FORAGE DIET. WE HYPOTHESIZE THAT FEEDING BSS AND NITRATES MAY REDUCE ENTERIC H2S AND CH4 PRODUCTION WITHOUT NEGATIVELY AFFECTING RUMINAL FERMENTATION AND METABOLISM.ASSESS THE EFFECT OF BSS IN COMBINATION WITH NITRATE ON PERFORMANCE OF GROWING CATTLE CONSUMING A LOW-QUALITY, HIGH-S, FORAGE-BASED DIET. WE HYPOTHESIZE THAT CATTLE CONSUMING LOW-QUALITY, HIGH-S DIETS SUPPLEMENTED WITH BSS AND NITRATES WILL PRESENT GREATER PERFORMANCE AND IMPROVED MINERAL STATUS THAN THOSE WITHOUT BSS AND NITRATES.ASSESS THE EFFECT OF BSS IN COMBINATION WITH NITRATE ON PERFORMANCE OF FEEDLOT CATTLE CONSUMING A HIGH-GRAIN DIET WITH INCLUSION OF HIGH-SULFUR BYPRODUCTS. WE HYPOTHESIZE THAT FEEDLOT CATTLE CONSUMING A HIGH-GRAIN DIET SUPPLEMENTED WITH BSS AND NITRATES WILL PRESENT GREATER PERFORMANCE THAN THOSE WITHOUT BSS AND NITRATES.THE EXPECTED RESULTS FROM THIS STUDY ARE THAT NITRATE AND BISMUTH SUBSALICYLATE MAY PROVIDE AN ALTERNATIVE TO DECREASE GREENHOUSE GAS EMISSIONS BY CATTLE CONSUMING HIGH-FORAGE DIETS. ADDITIONALLY, THE INCLUSION OF NITRATES AS A SUPPLEMENT WOULD IMPROVE THE NUTRITIONAL STATUS OF CATTLE BY INCREASING THE PROTEIN SUPPLY, RESULTING IN INCREASED GROWTH PERFORMANCE.THE ANTICIPATED IMPACT OF THIS PROJECT IS EVIDENCED BY THE POTENTIAL OF DECREASING THE NEGATIVE EFFECTS OF HIGH SULFUR DIETS, WHICH HAS BEEN ESTIMATED TO COST THE U.S. BEEF INDUSTRY AN ANNUAL $7.4 MILLION, CONSIDERING ONLY THE EFFECTS ON HIGH-GRAIN DIETS. BECAUSE METHANE IS BOTH AN ENVIRONMENTAL POLLUTANT AND AN ENERGY LOSS TO CATTLE, MITIGATING METHANE EMISSIONS SHOULD ENHANCE THE PRODUCTION EFFICIENCY OF RUMINANTS, LEADING TO IMPROVEMENTS IN THE EFFICIENCY OF CONVERSION OF GRASS OR FIBROUS BYPRODUCTS INTO ANIMAL PROTEIN.