Divergent selection for shape of growth curve in Japanese quail. 5. Growth pattern and low protein level in starter diet.

1. The effect of crude protein (CP) concentration in starter diet (259 or 216 g CP and 11.7 MJ ME/kg, fed from 0 to 21 d of age) on postnatal growth pattern (from hatching to 70 d of age) was analysed in Japanese quail lines divergently selected for high (HG) and low (LG) relative gain of body weight (BW) between 11 and 28 d of age, and constant BW at 49 d of age. 2. Males and females of both lines fed on the low CP diet showed a transient BW retardation between 7 and 28 d of age, and 7 and 35 d of age, respectively, when compared with their counterparts receiving the standard CP diet. 3. Although the negative effect of low CP concentration on growth rate was observed in both lines, a lower tolerance of young HG vs. LG quail to the reduction of CP level in food was evident from their (i) stronger BW retardation at 14 d of age (16 vs. 7%), (ii) more delayed onset of compensatory growth (21 vs. 7 d of age) and (iii) greater prolongation of the acceleration growth phase (3 vs. 1 d of age) following insufficient dietary CP. 4. The line differences in early growth rate were accompanied by significant differences in food intake. The LG line consumed more food than the HG line on both CP diets and consumption was not influenced by food quality. In contrast, HG quail reduced food intake with the decrease of dietary CP concentration. On both CP diets, this was associated with a higher body fatness of LG vs. HG quail. 5. The protein-deficient food could thus represent an important factor contributing to the selection advantage of developmentally accelerated genotypes during the selection for high BW in young age categories.