With the rising atmospheric CO2, crops will assimilate more carbon. Yields will increase in terms of carbohydrates while diluting the content of protein and minerals in compound pig feed, calling for an altered formulation with more protein and less carbohydrate crops to maintain its nutritional value. Using crop response data from CO2 exposures in a linear modeling of feed formulation, we apply a consequential life cycle assessment (cLCA) to model all of the environmental impacts and socio-economic consequences that altered crop yields and chemical composition at elevated CO2 levels have on feed formulation, targeting altered amino acid contents rather than overall protein. An atmospheric CO2 of 550 µmole mole−1 gives rise to a 6% smaller demand for land use for pig feed production. However, feed produced at this CO2 must include 23% more soymeal and 5% less wheat than at present in order to keep its nutritional value. This counteracts the yield benefit. The monetized environmental cost of producing pig feed, where sunflower and soy contribute the most, equals the direct feed price in both scenarios. If external costs were internalized, honoring the Rio Declaration, feed prices would double. In contrast, the future composition of pig feed will increase the direct price by only 0.8%, while the external cost decreases by only 0.3%.