Maternal care is essential to optimally support survival of the offspring. During evolution of mammalian species, different phenotypes have evolved in relation to gestation length, number, size, and maturation stage of the offspring at parturition, as well as colostrum and milk composition. The aim of the present review is to describe relationships between placental function and colostrum and milk composition in different mammalian species. Species covered in this article include humans, rabbits, rodents (rat and mouse), carnivores (cats and dogs), and a variety of ungulate species (cattle, sheep, goats, pigs, and horses). Species-specific aspects are elucidated with a special focus on the transfer of passive immunity. In this regard, the structure and thus the capability of the placenta to transport immunoglobulins from maternal to fetal circulation in utero dictates the necessity of the passive transfer of immunity via colostrum. Consequently, species with exclusive postpartal transfer of immunity such as in all ungulate species have greater immunoglobulin G concentrations in colostrum than species with a prepartal transfer in utero, where especially immunoglobulin A with its local immune function in the gastrointestinal tract is present in colostrum (e.g., rabbit and human). In terms of the nutritional purpose, suckling frequency is an important factor determining the gross composition of colostrum as well as in the mature milk of these species. Milk of nidicolous animals with long intervals in-between suckling events contains more fat than milk of nidifugous animals with constant access to their mother. However, the importance of colostrum and milk consumption for newborn animals and human babies goes beyond nutrition and the transfer of immunity. Numerous bioactive components such as growth factors, hormones, and oligosaccharides are enriched in colostrum and transition milk, which support the development of the intestinal tract and local immune system.
Keywords: colostrum; mammals; mammary gland; placenta; transfer of passive immunity.
During evolution of mammalians, intrinsic strategies and components of maternal care during the transition from pregnancy to lactation have evolved into a broad variety in gestation length, number, size, and maturation stage of the offspring at parturition, and colostrum and milk composition. The original purpose of immuno-protective glandular secretions is still conserved in many mammalian species, where colostrum, that is, the very first milk obtained after parturition, contains the greatest amounts of immunoglobulins, leukocytes, lysozyme, lactoferrin, oligosaccharides, etc. Apart from its nutritive function, bioactive components in colostrum and milk support the development of gastrointestinal structures and intestinal microflora. Depending on the placentation type and intrauterine transfer of immunoglobulins, the survival of the neonate depends more or less on the passive transfer of immunoglobulins via colostrum. The aim of the present review is to describe relationships between placenta function and colostrum (and milk, respectively) composition in different mammalian species. Special attention is paid to the transfer of passive immunity from the dam to the offspring.
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