Estimation of human-edible protein conversion efficiency, net protein contribution, and enteric methane production from beef production in the United States.
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A model was developed to estimate beef's contribution toward meeting human protein requirements using a summative model of net protein contribution (NPC) and methane production. NPC was calculated by multiplying the ratio of human-edible protein (HeP) in beef to the HeP in feedstuffs by the protein quality ratio (PQR). PQR describes the change in biological value of HeP that occurs when plant-derived HeP is converted to beef. An NPC > 1 indicates that the production system is positively contributing to meeting human requirements; systems with NPC < 1 reduce the net protein available to meet human requirements. Scenarios were arranged as a 2 2 factorial with two sets of dietary inputs and two sets of production parameters. Dietary inputs represented either inputs used in a previous report estimating HeP (previous diet; PD) or inputs more representative of conventional beef production systems (current diet; CD). Production parameters were either drawn from previous reports (previous parameters; PP) or chosen to characterize current industry standards (current parameters; CP). The HeP conversion efficiency (HePCE) for current industry diets and production parameters (CDCP) (kg HeP yield/kg HeP input) was greatest in the cow-calf sector (2,640.83) compared with stocker (5.22) and feedlot (0.34), and other scenarios followed a similar trend. In addition, the entire production system had an HePCE of 0.99 for CDCP; the previous model diets and production parameters (PDPP) scenario estimated HePCE to be 0.46, and other scenarios were in between. For the CDCP scenario, 56%, 10%, and 34% of the HeP were produced in the cow-calf, stocker, and feedlot sectors; PDPP was similar (59%, 13%, and 28%, respectively). PQR averaged 3.04, 3.04, and 2.64 for cow-calf, stocker, and feedlot sectors, respectively, indicating each sector enhances the biological value of the HeP fed. The NPC was greatest for the cow-calf sector (8,794), followed by the stocker and feedlot sectors (8.85 and 0.23, respectively). The entire beef value chain had a PQR of 2.68 and NPC ranged from 1.01 to 3.11, which correspond to PDPP and CDCP, respectively. Overall, 3.05 kg of CH4 were produced per kilogram HeP for CDCP and 2.58 for PDPP, with the cow-calf sector being greater than the feedlot sector (4.53 vs. 0.94 kg CH4/kg HeP, CDCP). Our results suggest that each individual beef sector and the entire value chain produce more high-quality HeP than is consumed in production. Accordingly, beef is a net contributor to meeting human protein requirements.
