An investigation was undertaken to manipulate the embryonic growth and post hatch gain by in ovo injection of amino acids (AA) and dietary supplementation of critical essential AA during successive starting (0-3 wk) and finishing (3-6 wk) growth phases. In ovo injection of amino acids with either 22 mm needle at broad end or 11 mm needle at narrow end had no adverse effect on hatchability. In ovo injection with 0.5% of total egg amino acids on 14th d of incubation had 73 g higher live weight gain at 6th wk of age as compared to un-injected control. In ovo injection of specific Aas i.e. combination of Glycine + Proline, Leucine + Isoleucine + Valine and Threonine + Glycine + Serine AA had higher chick weight, body weight and better immune response at 3rd wk of age. In ovo injection of amino acid did not affect the growth of immune organs, digestive organs and percent carcass yield. The diets formulated on digestible AA had higher body weight and improved feed conversion efficiency than total AA basis. There was no difference in the body weight and FCR of the bird fed 100 and 115% AA of NRC (1994) translated to 3000 kcal ME/kg rather than 3200 kcal as specified by NRC (1994). The performance of the birds was also not affected by feeding diets with or without animal protein, when the balances of amino acids were met by supplementing the synthetic amino acids. The economic return was higher in low levels of dietary amino acids. Amino acid levels did not affect the immune response and weight of immune organ. Digestive organ weights were higher in all vegetable meal than fishmeal based diets and in low AA and low ME diets. Cell mediated immune response was higher in low level of AA, while humoral immune response was higher in high energy diets. Low AA and high-energy diets accrued more fat deposition, while breast yield was higher in 115% AA. Breast yield was influenced by AA levels of the diet, whereas ME levels had no effect on the cut-up yields. Nitrogen retention was improved on manipulation of limiting amino acids to 115% of requirement, whereas dietary energy levels did not affect N retention and N loss. The daily requirement of CP, ME, Lys, Met and Thr for maintenance and live weight gain during starting period were 5.56 g, 216 kcal, 216 mg, 88 mg and 199 mg/W0.75 kg and 288 mg, 3.23 kcal, 15 mg, 10.5 mg and 10 mg/g gain, respectively. Based on the weight gain during 0-3 wk period, the requirement of Lys, Met and Thr were predicted as 1.17, 0.75 and 0.86% of the diet, respectively and the ideal ratio of those AA were 100:64:72. The daily requirement of CP, ME, Lys, Met and Thr for maintenance and live weight gain during finishing period were 13.02 g, 129.5 kcal, 588 mg, 238 mg and 699 mg/W0.75 kg and 182 mg, 3.92 kcal, 8.6 mg, 3.8 mg and 1.8 mg/g gain, respectively. The requirement of Lys, Met and Thr were predicted as 1.00, 0.42 and 0.67% of the diet, respectively based on the weight gain during 0-3 wk period and the ideal ratio of those AA were 100:42:67. Feeding standard has been developed for both starting and finishing period based on the predicted values, which will be suitable for tropical conditions like India. The study envisaged future scope for identification of specific amino acid(s) manipulating growth of embryo and digestive organs and as immunomodulator and production of designer chicks having nutritive and therapeutic value.
