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A total of 1110 broiler cockerels were used in three experiments to determine the availability of iron and copper from various sources. A skim milk basal diet was fed in each experiment using chicks maintained in battery brooders beginning at one day of age. Four organic iron compounds (sequestered iron A 1 and ferric choline chloride 2 in Experiment 1 and sequestered iron B and C 1 in Experiment 2), ferrous sulfate and ferric oxide were the test iron compounds used in Experiments 1 and 2. Added dietary iron levels furnished by the test compounds were 10 and 20 p.p.m. (Experiment 1) and 5 and 10 p.p.m. (Experiment 2). The test copper compounds fed in Experiment 3 were added to furnish 1 and 2 p.p.m. copper using cupric sulfate, cuprous oxide and cuprous iodide. No consistent differences in hemoglobin content, hematocrit (packed cell volume), chick weight and mortality were observed between ferrous sulfate and the four organic iron compounds; however, these compounds were significantly superior to ferric oxide. Hemoglobin content, hematocrit and liver copper content were significantly increased when cupric sulfate was fed as compared to results obtained with cuprous iodide or cuprous oxide. Increased chick weight gain and decreased mortality were observed with chicks fed cupric sulfate or cuprous iodide as compared to those fed cuprous oxide. Chick availability values for ferric oxide (71 and 82%) were approximately three-quarters that of ferrous sulfate. The organic sources of iron gave high availability values (91–131%), although ferric choline chloride was not as available to the chick as the sequestered iron compounds (93–131%) as determined by regression analysis method and relative biological availability. Cuprous iodide and cuprous oxide have essentially equal availability, but the availability of these copper sources is only three-quarters that of cupric sulfate.

Seven feed grade phosphates were assayed biologically using tibia bone ash as the response criterion. Phosphorus solubility in (1) 0.4% hydrochloric acid, (2) 2 % citric acid and (3) neutral ammonium citrate was determined for each sample. There was very little, if any, agreement between phosphorus solubility in the dilute acid solutions and bio-availability. Of the three experimental tests, solubility in 0.4% hydrochloric acid appeared to be the most promising for predicting bio-availability, but even with this method the agreement with bioassay results was poor.

Four experiments were conducted using a total of 1480 broiler strain cockerels to determine the effect of particle size and source of calcium on chick weight and tibia ash. The particle sizes of the test calcium sources obtained from oyster shell and limestone were defined as 6–8, 16–20, 40–50, 100–140, and 270–Pan on a passed-retained basis using the U.S.B.S. sieve series. Non-screened samples of oyster shell, limestone and a mined marine source were also tested. No consistent differences in growth rate and percent tibia ash were observed between oyster shell and limestone when the particle size of these supplements was equal. Increased weight gains were obtained with the medium and fine particle sizes (U.S.B.S. 16–Pan) as compared to the larger sizes (U.S.B.S. 6–8). Tibia ash was significantly increased when the particle size of the calcium supplement was medium (U.S.B.S. 40–50) as compared to the ash values obtained by feeding either the smallest (U.S.B.S. 270–Pan) or largest (U.S.B.S. 6–8) particle sizes. Screen analyses of commercial limestone, oyster shell and the mined marine calcium source revealed that the commercial oyster shell was a larger sized material than either limestone or the mined marine source tested in this study. Increased tibia ash was obtained by feeding the commercial oyster shell product which verifies the need for a medium particle size (16–50) in the chick’s diet. These data indicate calcium utilization by the chick is dependent upon the particle size of the calcium supplement. It appears desirable to use a medium to fine (U.S.B.S. 16–Pan) particle size calcium supplement in chick diets when considering both chick weight and percent tibia ash.