HOW DO MANAGEMENT DECISIONS IMPACT THE SUSTAINABILITY OF UPPER MIDWEST BEEF CATTLE GRAZING?

The conversion of grass to beef is less efficient than the process of converting feed to human-edible protein in nonruminants, although ruminal fermentation does allow for the utilization of complex carbohydrates. This has resulted in the cattle industry receiving increased attention due to its perceived high carbon (C) footprint. While ruminants have evolved to fill the niche of converting human inedible carbohydrates into usable end-products for growth, this process results in considerable greenhouse gas (GHG) emissions as byproducts of the reticulo-rumen fermentation process. Life Cycle Assessments have shown that the grazing sector of the cattle industry, cow-calf and stocker cattle, may be responsible for 70 to 80% of the industry’s total C footprint. Therefore, research is needed to explore the soil-plant-animal interrelationships and generate data to provide management recommendations to producers to improve the C footprint of their operation. As it relates to agriculture, sustainability has three legs that must be met addressed to improve its sustainability: 1) social- the strategy must maintain social license to operate, 2) environmental- the strategy must reduce negative environmental consequences, and 3) economic- producers must remain economically viable. This dissertation examines how management decisions impact grazing beef cattle through two of the three legs of sustainability: environmental and economic sustainability. The literature review focuses on the role on enteric methane on the C footprint of the beef industry, as this topic “keeps the lights on” in many laboratories due to increased consumer concern about the industry’s C footprint. However, key nutritional abatement strategies that goes beyond enteric methane are management decisions that improve the efficiency of ruminal fermentation. Matching cows to the production environment is a critical management decision, as selecting cows too small or too large would result in an inefficient utilization of the forage base. This idea is explored chapter 2, modeling the biological and economic output of a Michigan beef herd. We conducted a backwards looking enterprise budget analysis and forward-looking net present value analysis on the Lake City AgBioResearch Center Red Angus herd to determine what size cow best fits the present production environment. We found that as cow size increased, within the range of cow body weights of 430.83 to 634.92 kg, calculated net returns per unit of land decreased by $10.27/ha. The last two chapters compare environmental tradeoffs between two different forage mixtures grazed by beef cattle: a biologically diverse, mixed-specie pasture (COMP), and a simple binary mixture of alfalfa:orchardgrass (SIMP). The hypothesis was that the COMP mixture would have reduced enteric methane production, increased forage productivity due to the diversity of the mixture, and greater soil C accumulation. Both treatments performed similarly in animal performance, soil GHG fluxes, and soil organic C and total N stocks. Animals grazing COMP mixtures tended to have lower enteric CH4 emissions compared to SIMP, but there was no difference in emission intensity across three grazing seasons. This project serves to supplement the dearth of literature comparing a simple and diverse forage mixture. More research on the long-term performance of the diverse and simple forage mixtures and the utilization of new technologies such as eddy covariance flux towers will help provide a more robust examination on the environmental tradeoffs between forage mixtures than the methodologies utilized in this experiment.