Table 3. Effect of different content on protein intake and nitrogen utilization of male Pekin ducks for 21 days after hatching1)

Item Dietary protein content (%) SEM p-value
15 17 19 21 23 25
Protein intake (g)
 Day 7 5.55e 6.49d 7.69c 8.09b 9.04a 9.36a 0.202 0.001
 Day 14 14.63f 16.34e 19.28d 20.20c 21.83b 24.83a 0.498 0.001
 Day 21 22.29f 25.70e 28.91d 30.96c 34.24b 35.77a 0.703 0.001
 Day 1–21 14.16f 16.18e 18.63d 19.75c 21.71b 23.32a 0.46 0.001
Nitrogen retention (g)
 Day 1–21 36.92c 38.50b 39.87a 40.87a 40.57a 39.84a 0.258 0.001
Nitrogen excretion (g)
 Day 1–21 10.65f 15.85e 22.72d 25.49c 32.36b 38.52a 1.383 0.001
Each value is the mean of 6 replicates (12 birds per cage).
Means in the same row with different superscripts differ in the level of crude protein content (p < 0.05).