Interaction between dietary calcium and non-phytate phosphorus levels on growth, bone mineralization and mineral excretion in commercial broilers

An experiment was conducted to study the interaction between the levels of dietary calcium (Ca) and non-phytate phosphorus (NPP) on growth, bone mineralization and mineral excretion in commercial broilers. Day-old Vencob female broiler chicks (n = 720) were distributed into 144 stainless steel battery brooders, five birds in each. Four levels each of Ca (6, 7, 8 and 9 g kg(-1)) and NPP (3, 3.5, 4 and 4.5 g kg(-1)) were fed in a factorial design through a maize-soya basal diet. Levels of maize, dicalcium phosphate and oyster shell powder were adjusted to obtain the desired levels of Ca and NPP. Each diet was fed ad libitum to chicks in 9 battery brooders from day 1 to 42 days of age. Body weight gain, feed intake and tibia breaking strength were depressed (P < 0.01) and leg abnormality score increased with increase in level of Ca at lower levels of NPP (3 and 3.5 g kg-' diet) at 14, 28 and 42 days of age. These ill effects were alleviated by reducing the levels of Ca to the minimum levels tested. Tibia breaking strength and tibia ash content in broilers fed the lowest levels of Ca and NPP (6 and 3 g kg(-1), respectively) were similar to those fed diets with highest level of these minerals (9 and 4.5 g kg(-1), respectively) in diet. Excretion of Ca, P and Fe was lower in broilers fed the lowest levels of minerals (6 g Ca and 3 g NPP kg(-1)) compared to the higher levels. The requirements of Ca and NPP for perfon-nance and bone mineralization were predicted using surface regression analysis. Increase in the level of Ca and NPP above the minimum levels tested did not further improve the variables studied. Based on the data, it could be concluded that levels of 6g Ca and 3.75 g NPP kg(-1) diet would be adequate for commercial broilers from day 1 to 42 days of age. (c) 2006 Elsevier B.V. All rights reserved.