Despite much promise in agriculture — for example, in the engineering of a high proportion of essential amino acids into staple food proteins — the first example of a tailored enzyme being introduced into crop plants (to produce stearate and increase the proportion of unsaturated fatty acids in seed oil) has only recently taken place. Enzymes are used increasingly as supplements to animal feeds to aid the digestion of celluloses and the release of phosphorus from phytic acids. The increasing prominence of engineered phytases is a response to concerns over bovine spongiform encephalopathy (BSE) and the shunning of traditional bone-meal sources of phosphorus