Greenhouse-gas emissions of beef finishing systems in the Southern High Plains

Abstract

Greenhouse gases (GHG) have been implicated in global warming and climate change. While life cycle assessments (LCA) and GHG studies have been conducted for numerous agricultural commodities, there has been little effort to estimate GHG (CO2, N2O, and CH4) from beef finishing systems of the Southern High Plains (SHP) region, which produces approximately 30% of the United States beef. The objective of this research was to quantify the carbon footprint of five beef-finishing systems using a dynamic, systems-based model that calculated CO2e emissions attributable to both animal gain and manure management. The systems consisted of native grass pasture (NGP, System 1); native grass pasture with feedyard finishing (NGP-FY, System 2); wheat pasture with feedyard finishing (WP-FY, System 3); feedyard-only (FY, System 4); and native grass pasture, wheat pasture, and feedyard finishing (NGP-WP-FY, System 5). Although rarely used, the NGP was included as a baseline. Variables in the model and associated management decisions were based on feed type, nutritional content, feed source, and hauling distance. The starting point of the model was a weaned steer (250 kg) and the endpoint was a steer which would grade “choice” (28% body fat) or 30 months in age, whichever came first. Overall CO2e kg−1 gain decreased when cattle were fed high-quality diets and were intensively managed for production in the shortest time possible. The FY produced the desired carcass in the shortest time with the lowest cumulative emissions. The FY also had the highest average daily gain, lowest dry matter and water intake, as well as manure production. Net GHG emissions from FY were 4.84 kg CO2e kg−1 gain (1799 kg CO2e animal−1). Net GHG emissions from NGP-FY, WP-FY, NGP-WP-FY, and NGP were 1.62, 1.81, 2.08, and 3.69 times that of FY, respectively. These results suggest that intensive feeding and management of beef cattle in the FY system result in the lowest overall CO2e emissions to produce a mature steer. Consequently, feeding systems that include native grass and wheat pasture have proportionately larger amounts of CO2e emissions.