Effects of 500 and 1000 FTU/kg phytase supplementation of maize-based diets with two tiers of nutrient specifications on performance of broiler chickens

• The utilisation of phytase in maize-based broiler diets was evaluated.
• Diets contained two tiers of reduced nutrient specifications.
• Both standard and elevated phytase inclusions recovered growth performance.
• Both standard and elevated phytase inclusions recovered nutrient utilisation.
• Both standard and elevated phytase inclusions recovered mineral retention.

Starter, grower and finisher maize-based diets (Diets A) were formulated to marginal nutrient specifications and offered to broilers from 1 to 14, 15 to 27, and 28 to 40 days post-hatch, respectively. Nutrient specifications were reduced (Diets B) and offered to broilers without and with 500 FTU/kg phytase; specifications were further reduced to create a second tier of reduced nutrient specifications (Diets C) without and with 1000 FTU/kg phytase. The study was conducted using 240 male Ross 308 chicks with each of the 5 treatments consisting of 8 replicates of 6 birds per replicate. Growth performance was monitored during each phase of the grow-out period, mineral retentions were determined in the grower phase and nutrient utilisation in the finisher phase. Apparent digestibility coefficients of nitrogen were determined in the proximal jejunum, distal jejunum, proximal ileum and distal ileum in broilers at 40 days post-hatch. In addition, N digestion rates (Knitrogen) were determined. Over the 40-day feeding period, declining nutrient specifications decreased weight gains in broilers offered non-supplemented diets from 2721 (Diets A) to 2627 (Diets B) and 2525 g/bird (Diets C) and increased FCR from 1.551 to 1.577 and 1.605 in the corresponding diets. The differences in weight gain (7.20%) and FCR (3.48%) between Diets A and Diets C were significant (P < 0.05). From 1 to 40 days post-hatch, phytase improved weight gain in broilers offered diets B by 11.8% (P < 0. 001) and those offered diets C by 13.4% (P < 0. 001) and both treatments outperformed diets A (P < 0. 001). Phytase enhanced FCR in chicks offered diets C by 3.80% (1.544 versus 1.605, P < 0.05). Phytase supplementation of diets B increased AMEn by 0.23 MJ (P < 0.05). Phytase supplementation of diets C increased AME by 0.41 MJ (P < 0.001), AME:GE ratios by 2.62% (P < 0.001) and N retention by 5.4 percentage units (P < 0.001). Phytase enhanced retentions of calcium, phosphorus, and sodium in both diets B and C (P < 0.001). Phytase supplementation of diets B improved (P < 0.01) apparent digestibility coefficients of nitrogen at four small intestinal sites with increases ranging from 79.9% (proximal jejunum) to 11.3% (distal ileum) culminating in an increase (P < 0.01) in N digestion rates (Knitrogen) of 64% from 2.59 to 4.24 × 10−2 min−1. Phytase supplementation of diets C increased N digestibility in the distal ileum by 7.63% (P < 0.001) and N digestion rates by 35% from 3.65 to 4.91 × 10−2 min−1 (P < 0.01). In conclusion, standard (500 FTU/kg) and elevated (1000 FTU/kg) phytase inclusions in diets with reduced nutrient specifications have the capacity to enhance performance of broilers and compensate for these reductions.