Effects of Supplemental Protease and Diet Type on Energy Utilisation and Nutrient Digestibility of Broilers from 9 to 22 Days of Age

Dietary protease supplementation has been observed to improve broiler growth performance and amino acid digestibility (Angel et al., 2011; Fru-Nji et al., 2011). Improvements in broiler energy utilisation have also been observed with supplemental protease (Sorbara, 2009; Freitas et al., 2011). These positive extra-proteinaceous effects may be influenced by age and diet type. In addition, these effects may vary throughout the broiler small intestine. Therefore, an experiment was conducted to evaluate the effects of supplemental protease and diet type on apparent metabolizable energy (AME) and nutrient digestibility in broilers from 9 to 22 d of age.

At hatch, a total of 400 Cobb 500 mixed-sex broilers were obtained from a local hatchery, distributed into 4 large floor pens, and were offered 1 of 4 dietary treatments. At 6 d of age, 336 birds (84 from each of the 4 treatment groups) were weighed and distributed into 56 battery cages (6 birds per cage; 14 replicates per treatment) in a randomised complete block design. Dietary treatments consisted of a 2 × 2 factorial arrangement with diet type (corn- or wheat-based) and protease inclusion (0 or 200 mg/kg) as the main factors. Feed was provided in 2 phases; starter (1 to 14 d of age; crumbles) and grower (15 to 22 d of age; pellets). All diets were formulated to contain phytase (supplemented at 200 mg/kg) and xylanase (supplemented at 200 mg/kg). Excreta and feed intake were collected and recorded from 9 to 11 and 19 to 21 d of age for AME determination, total-tract N and starch digestibility. At 22 d of age, jejunal and ileal digesta contents from 4 birds per cage were collected, pooled, and analysed for Ti, N, starch, and gross energy concentrations for apparent N and starch digestibility and digestible energy (DE).

Diet type influenced (P < 0.05) total-tract N and starch digestibility, and AME from 9 to 11 d of age; and N digestibility and AME from 19 to 21 d of age. Broilers offered corn-based diets had higher total-tract N and starch digestibility coefficients and AME than those offered wheat-based diets. The effect of protease was greater (P < 0.05) for jejunal (N, starch, DE) and ileal (N and DE) digestibility in the corn-based diet compared with the wheat-based diet, resulting in a diet type by protease inclusion interaction. Birds offered the wheat-based diets with and without protease and the corn-based diet with protease exhibited a higher jejunal and ileal N digestibility than those offered the corn-based diet without protease. Additionally, broilers offered the corn-based diet with protease exhibited the highest starch digestibility coefficient (jejunal) and DE (jejunal and ileal) of all treatments. A main effect of protease inclusion (P < 0.05) was also observed to affect ileal starch digestibility; broilers offered diets with protease had a higher digestibility coefficient than those without protease.

These results indicated that both energy utilisation and nutrient digestibility of broilers may be influenced by diet type and protease supplementation. Additional research is warranted to further quantify these effects and the modes of action responsible for these responses.