AFRC Institute for Grassland and Animal Production, Hurley, near Maidenhead, Berks SL6 5LR, UK

Keywords: mammary gland; cell culture; insulin-like growth factors; epidermal growth factor

Production of colostrum and milk in adequate quantities is essential for the survival of the young of most mammals. Preparation of the mammary gland for lactation takes place throughout fetal and post-natal life and results from many complex interactions. It involves the transformation of the gland from an epithelial anlagen in the fetus, through formation of a branched tubular structure to the fully developed lobulo-alveolar gland which has acquired the differentiated capacity to produce milk proteins, fat and sugar and, by milk ejection, to deliver these to the suckling. Mammary development has been reviewed extensively (see Cowie et al. , 1980; Mepham, 1983; Knight, 1984; Tucker, 1987, for recent reviews and further references).

The yield of the mammary gland is determined by numbers