Effects on chick growth of adding glycine, proline, glutamic acid or diammonium citrate to diets containing crystalline essential amino acids

Synopsis

Purified diets, designed to supply a balanced sufficiency but not excess of essential amino acids, were supplemented with glycine, glutamic acid, proline or diammonium citrate (DAC) and fed to broiler chicks from the 7 d stage. Slow growth was obtained unless the diet was supplemented with 1 % L‐proline, confirming other work which suggests that proline should be reclassified as an essential amino acid for the chick. Increasing the level of glycine in the diet from 1 ‐o to 1 ‐6% did not result in a marked growth response.

Adding 11–07% DAC to the diet gave a significant growth response and a significant increase in the plasma level of amino acids. The utilisation of DAC was equivalent to that of an isonitrogenous supplement of glutamic acid in one experiment, but was significantly poorer than that of glutamic acid in another.

A significant linear regression of live‐weight gain on nitrogen intake was derived (r = 0–8582): growth was better on a practical than on any of the purified diets used but was in close accordance with this relationship. Partition of the nitrogen intake into intakes of the various nitrogenous components gave more precise correlations. Use of intakes of essential amino acids, DAC, glutamic acid, proline and added glycine explained over 90% of the variance; use of essential amino acids, glutamic acid and proline explained over 83% of the variance.