According to Gary Cromwell, the landmark discoveries in swine nutrition over the past century include:
1. The recognition of protein quality, which has led to estimates of the amino acid content of feedstuffs, specific requirements, synthesis and use of crystalline amino acids in diets, and the concept of amino acid balance in diet formulation.
2. The development of the soybean crop from insignificant proportions to the major source of high quality protein for swine rations.
3. Studies in mineral nutrition and especially the determination of calcium and phosphorus requirements.
4. The discovery of vitamins, their isolation and synthesis, and studies which led to estimates of their requirements of pigs.