New research in npj Sustainable Agriculture finds that most life cycle assessments of farmed animal products leave out the mined mineral supplements added to feed. In a review of 109 LCAs, 64 percent excluded minerals entirely, and the omission was worst in aquaculture at 84 percent. That can understate the carbon footprint of meat, dairy, eggs, and farmed seafood, since mined phosphorus and zinc carry far higher embedded emissions per tonne than typical feed crops. Using a single proxy like limestone hides real differences across species. Laying hens need about four times more calcium than pigs, and farmed fish often need iron that cattle do not. The authors estimate that phosphorus supplements alone could add nearly 72 million tonnes of CO2 equivalent per year in US feedlots and another 164,000 tonnes for Norwegian salmon farming. They call for better data sharing from feed and mineral suppliers, plus more realistic proxies in LCA databases.
