Lactational Performance and Milk Composition in Relation to Duration of Pregnancy and Lactation

The dynamic changes that occur in milk composition associated with duration of lactation have been recognized for over a century as documented in several early publications some dating back to 1874 (1–3). In the mid 1900s Macy (4) reviewed 1500 publications on milk composition from many countries and selected 268 papers based on “the characteristics of subjects, methods of collecting samples, analytical techniques, diet and environmental factors”. From the data surveyed, they compiled a table of composite values for more than 50 components in human milk at three lactational stages: colostrum, representing one to five days postpartum; transitional milk, representing days six to ten postpartum; and mature milk, representing day 15 to 15 months postpartum. Since that time and particularly since the mid 1970s, a plethora of information on milk composition has emerged providing further characterization of important biological components in human milk and knowledge of those factors which are associated with alterations in the composition and volume of human milk produced by the average healthy lactating woman (Table 1).