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Two experiments were conducted to evaluate the calcium availability of 5 samples of ground limestone for chicks and laying hens. The first study employed broiler chicks to 4 weeks of age with body weight and bone ash as criteria of calcium availability. Regression analyses of the bone ash data showed a linear relationship between dietary calcium level and percent bone ash (fat-free, dry weight basis). A comparison of the slopes of the calculated regression lines showed that the percent calcium availability of the ground limestone samples varied from 73.3% to 109.4% in comparison with a calcium carbonate A.R. standard; oyster shell flour showed an availability of 107.8% by this method. The second study was carried out with laying hens and employed apparent calcium retention and egg shell thickness as criteria of calcium availability. The ground limestone samples varied from 82.4 to 98.4% calcium availability. Calcium, zinc, manganese, iron, and magnesium levels of twenty-four ground limestone and 5 oyster shell samples are reported.
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Reid et al. (1976) studied this question.
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