From the Editors: “Mammalian milk: The elixir of life from maternal care to modern dairy production”

Mammals are a unique class of animals where the females have mammary glands to produce milk for the sustenance and maternal care of their offspring. The availability of milk allows a high survival rate of the offspring after birth which is crucial after the great maternal investment on offspring development during the intrauterine period. The synthesis, storage and delivery of milk to the offspring requires development of the mammary gland prepartum and the postpartum production of colostrum and milk. However, not all mammals have developed the same strategy to produce milk and nourish their offspring. This issue of Animal Frontiers “Mammalian milk: The elixir of life from maternal care to modern dairy production” focuses on mammary gland development, colostrum production, genetic selection, metabolism, and the evolution of milk production that have enhanced the modern dairy cow and the dairy industry (Cole et al., 2023; Gross, 2023). The composition of milk differs considerably among species and is perfectly directed to the needs of the respective offspring. Therefore, this issue of Animal frontiers examines lactation in a variety of other species from mice (Höflich et al., 2023) to marine mammals (Avery and Zinn, 2023), from livestock [goats (Castro et al., 2023), horses (Reed and Reiter, 2023), and swine (Grahofer and Plush, 2023] to humans (Neville, 2023) and dogs and cats (Chastant, 2023). Mammary development, the proliferation and differentiation of mammary tissue, begins during the fetal life, increases in intensity during puberty, and is stimulated again during gestation. Mammary gland development and function are described in humans (Neville, 2023) and in various other species (Geiger and Hovey, 2023). Milk is the sole nutrition for the offspring as long as the young is unable to chew and digest feed from environmental sources. Mammary secretions must be ready for consumption by the offspring as soon the birth has taken place and the composition changes during the course of lactation. The first milk (colostrum) contains specific nutritive and non-nutritive constituents which facilitate the transition from intrauterine to parenteral nutrition. The special task of colostrum is the passive immunization of the newborn via its greater content of antibodies to bridge the first weeks of life until the offspring can produce its own antibodies (Baumrucker et al., 2023; Chastant, 2023; Reiter and Reed, 2023). Passive immunization through colostrum is particularly important in ungulate species because the placenta does not allow for the in-utero transfer of antibodies from the mother to the offspring. Colostrum also contains various bioactive hormones, enzymes, and vitamins, which activate growth and development of the newborn (Baumrucker et al., 2023). Importantly, the composition and value of colostrum is influenced by the prepartum nutrition of the dam (Hare et al., 2023). In the mammalian evolution beginning about 200 Mio years ago, initial mammary secretions appeared to have mainly a protective, antimicrobial role, containing antimicrobial enzymes and carbohydrates with greater prebiotic than nutritive effects to protect the offspring. The nutritive value of mammary secretions developed later in evolution. Urashima and his colleagues describe the changes in mammary secretions from high lysozyme and oligosaccharide contents in early mammals to increasing alpha-lactalbumin and abundant secretion of free lactose representing the main carbohydrate source in most modern mammals (Urashima et al., 2023). Important prerequisite of a widely spread milk consumption all over the world past infancy was the development of a lactase persistence (i.e., lactose digestibility) in adult humans (Stock and Wells, 2023). The gained digestibility of lactose allows the consumption of non-fermented milk product throughout the adult life, and can be considered as the basis for the creation of the modern dairy industry in many parts of the world. Through intensive breeding the modern dairy cow produces milk far in excess of the immediate requirements of its own offspring, and milk of dairy cows is an important source of high-quality nutrients for the human. The paper from Baes and her colleagues in Canada (Cole et al., 2023) describes pros and cons of dairy cow breeding for high milk production including risk factors of metabolic and infectious diseases and reproduction problems. From a physiological point of view potential limits of high milk production are analyzed in the paper by Gross (2023). It is our intent that this issue of Animal Frontiers “Mammalian milk: The elixir of life from maternal care to modern dairy production” will serve as the backbone of the 2024 Biology of Lactation in Farm Animals (BOLFA) to be held in Bern Switzerland in August 2024. Dr. Rupert M. Bruckmaier is the head of the Veterinary Physiology of the Vetsuisse Faculty, University of Bern, Switzerland. He has been working on the physiology and endocrinology of lactating ruminants. His work contributed to the knowledge in the field of physiology and biotechnology of milk removal in different species, the metabolism of dairy cows, and the immune response of the mammary gland. Within his interest in mammary gland biology, colostrum secretion and composition has been an important topic to investigate the various immunological, endocrine and further bioactive components in colostrum. During all research activities, he has tried his best to support young scientists for their future career. Dr. Steven Zinn is a professor of Animal Science at the University of Connecticut. He joined the faculty at the University of Connecticut in 1990 after earning his BS degree from Cornell University and his MS and PhD degrees in the laboratory of H. Allen Tucker at Michigan State University. His research is focused on growth physiology and endocrinology in domestic species with an emphasis on maternal nutrition. From 2008 to 2013, Dr. Zinn was Editor-in-Chief of the Journal of Animal Science and is a founding member and the inaugural Editor-in-Chief of Animal Frontiers from 2011 to 2013. He served as President of ASAS from 2017 to 2018, was named an ASAS Fellow in 2015, and received the ASAS Morrison Award in 2021.

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