1 Production and utilization of milk 1.1 Introduction Milk is a fluid secreted by the female of all mamalian species, of which there are more than 4000, for the primary function of meeting the complete nutritional requirements of the neonate of the species. In addition, milk serves several physiological functions for the neonate. Most of the non- nutritional functions of milk are served by proteins and peptides which include immunoglobulins, enzymes and enzyme inhibitors, binding or car rier proteins, growth factors and antibacterial agents. Because the nutri tional and physiological requirements of each species are more or less unique, the composition of milk shows very marked inter-species differences Of the more than 4000 species of mammal, the milks of only about 180 have been analysed and, of these, the data for only about 50 species are onsidered to be reliable (sufficient number of samples, representative sampling, adequate coverage of the lactation period). Not surprisingly, the milks of the principal dairying species, i. e cow, goat, sheep and buffalo, and the human are among those that are well characterized. The gross compo- sition of milks from selected species is summarized in Table 1.1; very extensive data on the composition of bovine and human milk are contained in Jensen(1995) 1.2 Composition and variability of milk In addition to the principal constituents listed in Table 1.1, milk contains several hundred minor constituents, many of which, e.g. vitamins, metal ions and favour compounds, have a major impact on the nutritional, technoloy cal and sensoric properties of milk and dairy products. Many of these effects will be discussed in subsequent chapters die tik is a very variable biological fluid. In addition to interspecies rences(Table 1.1), the milk of any particular species varies with the dividuality of the animal, the breed (in the case of commercial dairying species), health(mastitis and other diseases), nutritional status, stage of lactation, age, interval between milkings, etc. In a bulked factory milk supply, variability due to many of these factors is evened out, but some variability will persist and will be quite large in situations where milk1 Production and utilization of milk 1.1 Introduction Milk is a fluid secreted by the female of all mamalian species, of which there are more than 4000, for the primary function of meeting the complete nutritional requirements of the neonate of the species. In addition, milk serves several physiological functions for the neonate. Most of the non￾nutritional functions of milk are served by proteins and peptides which include immunoglobulins, enzymes and enzyme inhibitors, binding or car￾rier proteins, growth factors and antibacterial agents. Because the nutri￾tional and physiological requirements of each species are more or less unique, the composition of milk shows very marked inter-species differences. Of the more than 4000 species of mammal, the milks of only about 180 have been analysed and, of these, the data for only about 50 species are considered to be reliable (sufficient number of samples, representative sampling, adequate coverage of the lactation period). Not surprisingly, the milks of the principal dairying species, i.e. cow, goat, sheep and buffalo, and the human are among those that are well characterized. The gross compo￾sition of milks from selected species is summarized in Table 1.1; very extensive data on the composition of bovine and human milk are contained in Jensen (1995). 1.2 Composition and variability of milk In addition to the principal constituents listed in Table 1.1, milk contains several hundred minor constituents, many of which, e.g. vitamins, metal ions and flavour compounds, have a major impact on the nutritional, technologi￾cal and sensoric properties of milk and dairy products. Many of these effects will be discussed in subsequent chapters. Milk is a very variable biological fluid. In addition to interspecies differences (Table 1.1), the milk of any particular species varies with the individuality of the animal, the breed (in the case of commercial dairying species), health (mastitis and other diseases), nutritional status, stage of lactation, age, interval between milkings, etc. In a bulked factory milk supply, variability due to many of these factors is evened out, but some variability will persist and will be quite large in situations where milk