Effect of Quantity of Dietary Calcium on Maintenance of Bone Integrity in Mature White Leghorn Male Chickens

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Abstract
Two experiments of 28 and 20 weeks duration, respectively, were conducted to determine the effect of level of dietary calcium on bone integrity in mature White Leghorn male chickens. A purified type diet containing blood fibrin to supply protein was fed. The diet was pelleted to improve acceptability. The blood fibrin was found to be the principal source of dietary calcium. In the second experiment, the fibrin was washed with an EDTA solution, thereby reducing the total dietary calcium from 0.03 to 0.0035%. In the first experiment the calcium-phosphorus ratio was 1.5:1 but in the second all diets contained 0.1% phosphorus. Plasma calcium was significantly reduced by low calcium intake but plasma phosphorus was reduced only in the first experiment when dietary phosphorus was also low. Blood alkaline phosphatase varied inversely with dietary calcium in both experiments. Hydroxyproline values, however, varied directly with the level of dietary calcium in experiment 1 but were not affected by dietary calcium in experiment 2. Bone ash, calcium and phosphorus were decreased by the low calcium diet only when dietary phosphorus was also low. Otherwise bone mineral was maintained even at 0.0035% dietary calcium, but between 0.025 and 0.05% were needed for normal plasma calcium and alkaline phosphatase. The results of a 47Ca balance experiment indicated that the calcium requirement of adult White Leghorn male chickens was 0.028% of the diet. This was equivalent to 7.98 mg calcium per kilogram weight daily. When daily calcium intake was less than this, bone mineral was retained tenaciously.