Growth performance of male broiler chickens in different growth phases in response to amino acid concentrations in the pre-starter diet

An experiment involving 720 one-day-old male broilers (Ross 308) was conducted to investigate the effects of graded levels of crude protein and standardized ileal digestible (SID) amino acids (AA) on growth performance during the pre-starter period (0 to 7 d), and to compare the subsequent growth performance of birds fed a commercial diet in the later phase (8 to 28 d). On d 1, all birds were individually weighed and allocated to six groups with eight replicate pens (15 birds/pen). Broilers were fed diets containing six different dietary SID AA levels relative to the 90 to 115% requirement for 7 d. From d 8 to 28, birds were fed a commercial diet containing nutrient levels meeting their dietary requirements. The body weight gain (BWG; <italic>p</italic> = 0.044) and gain-to-feed ratio (G:F; p = 0.005) of birds increased quadratically, and feed intake of birds linearly increased with increasing dietary AA concentration during d 0 to 7. Growth performance exhibited linear increases in later phases (<italic>p</italic> &lt; 0.05) until 28 d, except for G:F at 28 d. BWG (p = 0.001) and feed intake (<italic>p</italic> = 0.008) linearly increased compared to the 90% SID AA treatment, whereas G:F was not affected (<italic>p</italic> = 0.088) by dietary treatment. Additionally, feed intake of birds linearly increased (<italic>p</italic> &lt; 0.01) as dietary SID AA concentration increased. Following the transition to a commercial diet, body weight at 14, 21, and 28 d, BWG, feed intake, and G:F linearly increased (<italic>p</italic> &lt; 0.05). Overall, BWG and the growth rate of broilers aged 8 to 28 d also exhibited linear increments (<italic>p</italic> &lt; 0.01) by the dietary AA concentrations in diets during the first week. The study findings confirm the influence of dietary AA concentrations on the growth performance of broilers in the first week after hatch, demonstrating that this impact persists in the later growth stage. Therefore, ensuring sufficient dietary AA intake during the first week of life can enhance performance in later stages of development in broiler chickens.