study was conducted to evaluate the
effects of dietary protein level and protein digestibility
on the growth performance and carcass characteristics
of broilers from 1 to 35 d of age. Broiler chickens (n =
320) were fed 4 different ideal protein-balanced, isocaloric
diets in a 2 × 2 factorial design with 2 levels of
protein [high protein (HiPro; 20 and 18% or 200 and
180 g/kg) and low protein (LoPro; 18 and 16% or 180
and 160 g/kg) on d 1 to 14 and d 15 to 35, respectively]
and 2 levels of protein digestibility [high digestibility
(HiDig) and low digestibility (LoDig); approximately
85% and 80% CP digestibility, respectively]. The Hi-
Dig diets were formulated using soybean meal and
fishmeal, whereas the LoDig diets used wheat distillers
dried grains with solubles and meat and bone meal
as the primary protein sources. The standardized ileal
digestibility (SID) values of the wheat distillers dried
grains with solubles and meat and bone meal (56.5 and
72.0% SID for lysine, respectively) were measured before
the experiment to improve the accuracy of the diet
formulations. During the starter phase, the interaction
was significant for ADG; birds fed the LoPro-LoDig
diet grew slower than birds fed the other 3 diets (P <
0.05). During the grower phase, the interaction was significant
for ADFI; birds fed the LoPro-LoDig diet had
the lowest ADFI compared with those fed the other 3
diets. The interaction between protein level and digestibility
was significant for the SID of most of the AA
and was significantly higher for birds fed the HiPro-
HiDig diet compared with those fed the other 3 diets.
Total breast meat yield was significantly higher in birds
fed the HiPro diets than in those fed the LoPro diets,
whereas birds fed the HiDig diets had significantly
more abdominal fat than those fed the LoDig diets.
The results suggest that low-protein diets can support