Changes in the concentrations of the minor constituents of goat's milk during starvation and on refeeding of the lactating animal and their relationship to mammary gland metabolism.

1. Changes in the concentrations of the minor constituents of goat's milk were observed during 48 h starvation and on refeeding. 2. The concentrations of hexose phosphate and UDP-hexoses increased during starvation and decreased on refeeding. 3. The concentrations of phosphoenolpyruvate and glycerate 3-phosphate decreased during starvation and increased on refeeding. 4. Isocitrate:2-oxoglutarate increased during starvation and decreased on refeeding. 5. Changes in the minor constituents of milk can be explained in terms of the metabolic changes occurring in the mammary gland during starvation. It is proposed that changes in the concentrations of these metabolites in milk reflect changes in their concentrations in the cytosol or Golgi vesicles of the mammary gland.