Response of broiler chicks to essential and non-essential amino acid supplementation of low crude protein diets

A study was conducted to evaluate individual and combined responses of broiler chicks to non-essential crystalline amino acid supplementation of a low crude protein starter diet. Five-hundred-and-forty Ross 508-day-old male chicks were placed in 90 Petersime battery cages (6 chicks/cage). Birds were fed a pre-starter diet from placement until day 5 formulated to meet or exceed NRC (National Research Council, 1994. Nutrient Requirements of Poultry. 9th ed. (revised). National Academy Press, Washinngton, DC) recommendations. They were subsequently fed dietary treatments from 5 to 21 days of age. Treatments consisted of a control diet (220 g/kg CP), a low crude protein (180 g/kg) diet supplemented with l-Lys, dl-Met, l-Thr, and l-Ile, six treatments composed of individual additions of Gly, l-Ala, l-Asp, l-Glu, l-Pro or l-Leu to the low crude protein diet, and the low crude protein diet with the combined supplementation of the aforementioned amino acids. At day 13, the control and low crude protein diet supplemented with all the non-essential amino acids resulted in chicks with higher BW gain and feed conversion than all other treatments. At day 21, supplementation with Gly, Leu or Asp to the low crude protein diet resulted in similar BW gain of chicks fed the control diet. Supplementation with Gly or Leu to the low crude protein diet resulted in similar feed conversion to that of chicks fed the control diet. Feed intake was unaffected by dietary treatments. Chicks fed the low crude protein diet or the low crude protein diets supplemented with individual amino acids, except Leu, had lower blood plasma uric acid concentration than chicks fed the control. Nitrogen retention was lowest with the control diet. Results indicate that when feeding chicks a starter-phase diet reduced by 4% points in crude protein, there is additional need for non-essential nitrogen.