Two experiments were carried out to determine the nutritional requirement of calcium for broilers in growing (22 to 42 days), and finishing (43 to 53 days) phases. Three hundred and sixty Avian Farm broiler chicks (180 from each sex) were used in both trails. The first experiment lasted 21 days and the second one, 10 days. A completely randomized design was used in both experiments, with six treatments, six replications and 10 birds per experimental unity (five males and five females). Two basal diets were formulated to meet the birds nutritional requirements, except for the calcium, that remained deficient at the level of 0.16%. The basal diets in each experiment were supplemented with 0.0, 0.25, 0.50, 0.75, 1.00, and 1.25% calcium from calcium carbonate, resulting in the levels of 0.16, 0.41, 0.66, 0.91, 1.16 and 1.41% of calcium, and the treatments were used to estimated the calcium requirements of broilers. At the end of each experiment, 72 birds were sacrificed by cervical dislocation for the purpose of determining the tibia breaking strength and tibia obtained calcium and ash. Weight gain, feed:gain ratio, tibia calcium contents (percentage and gram), tibia breaking strength (kgf), ashes contents in the tibia (percentage and gram) were the evaluated variables. The calcium requirements were estimated using the quadratic regression model. According to the biological values observed for the chickens were suggested the calcium requirements estimates of 1.02 and 1.01% for broilers from 22 to 42 and 43 to 53 days old, respectively. However, according to the tibia breaking strength, the calcium requirement suggested for broilers from 22 to 42 and 43 to 53 days old would be 1.28 and 1.18% respectively.
calcium requirements; performance; bones; broiler chicks
