Evaluation of body calcium and phosphorus composition of the Cobb 700 genotype during growth

1. The amount of calcium and phosphorus in the empty, feather-free bodies of Cobb 700 breed males and females was measured from hatch to 15 weeks of age.2. A four-phase ad libitum feeding programme was used to feed 400 chicks of each sex. Feeds contained commercial levels of calcium and phosphorus which met or exceeded the requirements for energy, protein and amino acids. All birds were weighed weekly. Ten birds per sex were sampled at 0, 7, 14, 28, 42, 56, 70, 84 and 105 d of age. Defeathered birds were minced, freeze-dried and then analysed for protein, ash, calcium and phosphorus content.3. Amounts of Ca in males and females at 105 d averaged 54 and 37 g, respectively, and 105 d P content in males and females averaged 35 and 27 g, respectively. The allometry of ash, Ca and P with empty, feather-free body protein was assessed. Ash was isometric with body protein, while an allometric exponent greater than 1 was established for Ca and P with body protein.4. The allometric models and means for Ca and P relative to body protein were compared with models and means found in the literature. Comparison of the Ca/protein ratios with previous data suggested that modern broilers may not reach their potential bone mineral deposition with current dietary guidelines, even when growth rates were maximised.5. Theoretical allometric relationships between Ca and P in bone and bone-free body and body protein have now been proposed. The allometric relationship between Ca and P and empty, feather-free body protein offers a suitable way to model the growth of these minerals in the broiler body.