Mammary gland from lactating cows responded additively to individual essential amino acids in casein synthesis rate

Dairy cattle only capture about 25% of dietary N in milk protein, with the remainder being excreted. By coordinating AA supply with demand, mammary cells reduce recycling of AA to the splanchnic tissues, thereby increasing efficiency. Several essential AA regulate the rate of synthesis of casein by altering the phosphorylation state of intracellular signaling proteins that affect the activity of initiation (eIF) and elongation (eEF) factors (Appuhamy et al., 2012). Therefore, supplementing the specific AA that exert the most influence on pathways controlling eIF and eEF should allow a reduction in CP supply to the animal, which will increase post-absorptive efficiency and reduce N excretion. The objective of this study was to determine the quantitative responses in milk protein synthesis to individual essential AA in mammary tissue.