Changes in the plasma concentrations of free amino acids in relation to egg formation in the hen.

I. The changes occurring in the free amino acids of the plasma of laying hens in relation to egg formation have been investigated in fed and starved hens in three experiments, each with eight birds. 2. The mean concentrations of most amino acids and of the totals were higher at night than in the morning. 3. In general, egg formation was associated with increases in the concentrations of nonessential and decreases in the concentrations of essential amino acids. Cystine and glutamic acid tended to behave like the essential amino acids. 4. After 40 h starvation seven amino acids, particularly serine, histidine and lysine, increased in concentration and only three, proline, ornithine and arginine, decreased significantly. 5 , When eight cocks were injected with oestrogen most of the amino acids increased in concentration. The essential amino acids (with the exception of phenylalanine), serine, proline, cystine and ornithine showed the greatest increases. 6 . The results are discussed in relation to the possibility that the voluntary food intake of hens may be influenced by changes in the plasma levels of one or more essential amino acids associated with the synthesis of egg albumen. Arginine appeared to be the only amino acid that might possibly fulfil this role. 7. It was concluded that investigations of changes in the free amino acids of hen plasma are unlikely to provide a useful approach to a study of the amino acid requirements or the nutritive value of particular proteins for egg production.