Historical perspectives of lactation biology in the late 20th and early 21st centuries

The latter half of the 20^th century and the first half of the 21^st century will be recognized as the “Golden Age” of Lactation Biology. This period corresponded with the rise of systemic , metabolomic, molecular and genomic biology. It opens with the discovery of the structure of DNA and ends with the sequencing of the complete genomes of humans and all major domestic animal species including the dairy cow. This included the ability to identify polymorphisms in the nucleic acid sequence which can be tied to specific differences in cellular, tissue and animal performance. Prior to this period classic work using endocrine ablation and replacement studies identified the mammary gland as an endocrine dependent organ. In the early 1960’s the development of radio-immuno and radio-receptor assays permitted the study of the relationship between endocrine patterns and mammary function. The ability to measure nucleic acid content of tissues opened the door to study of factors regulating mammary growth. The development of high speed centrifugation in the 1960’s allowed separation of specific cell organelles and their membranes. The development of transmission and scanning electron microscopy permitted the study of the relationship between structure and function in the mammary secretory cell. The availability of radioactive isotopes opened the doors to the study of metabolic pathways and end products of metabolism. The development of concepts regarding the coordination of metabolism to support lactation integrated our understanding of nutrient partitioning and homeostasis. The ability to produce recombinant molecules and organisms permitted enhancement of lactation in farm animal species and the production of milk containing proteins of value to human medicine. These discoveries and others contributed to a vastly increased dairy farm productivity in the U.S. and world-wide. This review will include the discussion of the thought leaders and laboratories who labored in these fields to produce the harvest of knowledge we enjoy today.