It has been established that lactose is the major osmole in the milk of many mammalian species, and hence that the amount of water secreted is approximately proportional to the amount of lactose secreted. It is envisaged that reduction of the amount of lactose synthesised would allow a reduction of the amount of water in milk. This thesis studied the regulation of lactose synthesis in the mammary glands of goats by altering the flux of glucose and other intermediates of lactose synthesis. The consequent effects were determined by measuring the levels of various metabolites in milk. The mechanism of the reduction of milk yield brought about by twenty-four hour fasting in goats was explored by looking for perturbations in some of these parameters measured. Also, known differences between certain bovine genetic groups in water secretion were investigated by measurements in milk of trace metabolites involved in lactose synthesis. It was intended to further substantiate the paradigm that availability of glucose within mammary secretory cells of ruminants normally regulates lactose synthesis during midlactation. This widely held belief has not been supported by this research.