Quantifying carbon fluxes in pigs at different production stages: Intake, excretion, and retention.

A detailed understanding of how dietary carbon (C) is partitioned between excretion, gaseous emissions, and retention is essential for integrating C into current nutrient accounting frameworks, thereby bringing nutrient losses and gas emissions within a single standardized system. To support such integration, the present study aimed to construct C balance models for weaned pigs, grower-finisher pigs, and sows using extant prediction equations and established constants to estimate dietary C input and C outputs via excreta, gas emissions, and retention in body tissues. Predicted C balances showed variable agreement across production stages, with comparatively closer agreement observed in grower-finisher pigs. Estimates of C intake and C output via exhalation were generally consistent with reported values, whereas predictions of fecal, urinary, and enteric CH4 outputs showed greater deviation, indicating areas requiring further refinement. Overall, the models developed in this study offer a conceptual framework for incorporating C into a unified nutrient accounting system. The present study demonstrates the feasibility of combining existing equations to estimate C flows at the animal level, while also highlighting key uncertainties and data gaps that need to be addressed in future research.