Effect of low-protein diets with crystalline amino acid supplementation on egg production, blood parameters and nitrogen balance in laying Japanese quails

A total of 120 Japanese quails were randomly distributed into six dietary groups to evaluate the effect of low-crude protein (CP) diet supplemented with crystalline amino acids on productive and reproductive performance, blood parameters and nitrogen (N) balance. Treatments consisted of six different diets: a control diet (20% CP), a low-CP (16%) diet supplemented with threonine (Thr), valine (Val) and tryptophan (Trp), three low-CP diets supplemented with individual Thr, Val or Trp, and a low-CP diet supplemented with all aforementioned amino acids. None of the growth traits examined were influenced either by dietary treatments or by egg production (P > 0.05). The highest fertility percentages (88.2%) were observed in quails fed the low-CP diet without crystalline amino acids supplementation followed by low-CP diet supplemented with Val (86.2%), whereas the highest hatchability (from fertile eggs) percentage was observed in quails fed low-CP diet plus Trp. Egg shell percentages from quails fed the control diet were higher (P < 0.05) compared to other dietary treatments during the whole feeding period. Yolk percentage was decreased (P < 0.01) with the low-CP diet supplemented with amino acids. Blood protein and ammonia levels were decreased (P < 0.05) by reducing the dietary CP level or by supplementing amino acids to the low-CP diet. Reducing the CP level in the diet with amino acids supplementation in laying quails decreased the daily N excretion (P < 0.05). It is concluded that reducing the CP level in a diet supplemented with crystalline amino acids supports reproductive performance in quails, and is a valuable strategy for decreasing feeding cost and mitigating ammonia emission.