Abstract
The objective of this study was to evaluate the variance of starch digestibility in broilers individually fed diets without or with supplemental exogenous amylase. A total of 120 d-of-hatch male chicks were individually reared from 5 to 42 d in metallic cages and fed maize-based basal diets or diets containing 80 kilo-novo-α-amylase units/kg (60 birds or replicates per treatment). Beginning on d 7, feed intake, body weight gain, and feed conversion ratio were recorded; partial excreta collection was conducted every Monday, Wednesday, and Friday until 42 d, when all birds were sacrificed for individual collection of duodenal and ileal digesta. Lower feed intake (4,675 vs. 4,815 g) and feed conversion ratio (1.470 vs. 1.508) were observed in amylase-fed broilers during the overall period (7-43 d; P < 0.01), whereas body weight gain was not affected. Amylase supplementation improved total tract starch (TTS) digestibility (P < 0.05) on each day of excreta collection (except for d 28, where no difference was found), averaging 0.982 vs. 0.973 compared to basal-fed broilers from d 7 to 42. Both apparent ileal starch (AIS) digestibility and apparent metabolizable energy (AME(N)) were increased (P <0.05) from 0.968 to 0.976 and from 3,119 to 3,198 kcal/kg, respectively, with enzyme supplementation. Activity of amylase in the duodenum was higher (18.6 vs. 50.1 IU/g of digesta) in supplemented birds. Amylase supplementation led to a reduced coefficient of variation for both TTS (averaged 2.41 vs. 0.92% from 7 to 42 d) and AIS digestibilities (1.96 vs. 1.03%), as well as AME(N) (0.49 vs. 0.35%), when compared to the nonsupplemented group, indicating lower individual heterogenity. An age effect was detected for TTS digestibility, as both groups saw an increase during the first weeks (slightly more pronounced in the supplemented group); older birds (d 30 onwards) presented a lower TTS digestibility compared to ages between 7 and 25 d. In conclusion, amylase supplementation in maize diets for broilers can attenuate individual bird variation for starch and energy utilization by increasing amylase activity and enhancing starch digestibility.