Bone Strength of Height-Restricted Broilers as Affected by Levels of Calcium, Phosphorus, and Manganese

Three experiments were conducted to determine the effects of certain dietary minerals on humerus breaking strength of broilers grown for 7 weeks in colony cage floor pens 30 cm high or grown in regular floor pens. Data were also collected on tibia strength in the first two experiments. The following dietary factors were involved: Experiment 1 consisted of three diets with increasing amounts of calcium (Ca) and phosphorus (P) but constant Ca:P ratio of 1.3:1.0; Experiment 2 comprised four diets with different P levels but with Ca constant at .9%, causing the Ca:P ratio to vary from 1.8:1.0 to .8:1.0; Experiment 3 was made up of six diets with three increasing levels of Ca and P but a constant Ca:P ratio of 1.3:1.0 and two manganese levels in a factorial arrangement. Data from all three experiments showed humerus breaking strength for broilers grown in regular floor pens to be significantly greater than for those grown in colony cage floor pens. No significant difference was found in tibia strength due to pen type. In Experiment 1, tibia and humerus breaking strengths increased as dietary Ca and P increased. In Experiment 2, humerus breaking strength maximized with dietary P at .7 and .9%. In the final experiment, varying manganese (Mn) caused no statistically significant differences in humerus breaking strength. There was some evidence that high Mn levels may interfere with Ca and P absorption or utilization when these minerals are at low levels. These data show slight improvements can be made in humerus strength of height-restricted birds by increasing dietary Ca and P provided a Ca:P ratio of approximately 1.3:1.0 is maintained.