Ideal amino acid ratios for sows can be affected by several factors such as the number of fetuses, the number of mammary glands, and stage of gestation for gestating sows and the number of nursing piglets, the number of lactating mammary glands, and maternal tissue mobilization for lactating sows. Earlier work at University of Illinois showed that maternal tissue mobilization contributes large amounts of essential amino acids to milk production and mammary gland growth. However, contributions of threonine and leucine from maternal tissue mobilization are relatively smaller than other essential amino acids. This indicates that a sow with extensive tissue mobilization (first and second parity sows as examples) would require more threonine and leucine than a sow with minimal tissue mobilization (i.e., multiparous sows as examples) during lactation. Ideal amino acid ratios among Lys:Thr:Leu:Val:Arg can change from 100:59:115:77:72 to 100:75:128:78:22 as contributions of amino acids from tissue mobilization increases. Previous work at Texas Tech University and North Carolina State University showed that amino acid uses for fetal and mammary tissue accumulations increase by 19 to 24 fold after d 70 of gestation which increases amino acid needs for sows during late gestation. Moreover, fetal and mammary tissues accrete more leucine and arginine than other essential amino acids increasing needs of leucine and arginine during late gestation when fetal and mammary tissue growth mostly occurs. Increase in the number of fetuses and mammary glands would also increase maternal needs for leucine and arginine. Ideal amino acid ratios among Lys:Thr:Leu:Val:Arg can change from 100:79:88:65:89 to 100:71:95:66:98 as gestation progresses with fetal and mammary tissue growth. Considering dynamic changes in ideal protein for sows, a phase feeding has been suggested for gestating sows whereas a parity feeding has been suggested for lactating sows. It has been difficult to practice phase feeding and parity feeding in sow farms because of limitations with existing feeding systems. Recent advances in feeding systems with multiple feed lines or with abilities of delivering different rations within a barn could allow considering dynamic changes of ideal protein in feeding sows during gestation and lactation.