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Several experiments were conducted to determine if circulating 1,25 dihydroxycholecalciferol (1,25(OH)2 D3) concentrations correlated with the laying hens’ ability to calcify egg shells. Total Ca and 1,25(OH)2 D3 concentrations in plasma of hens selected to produce high quality egg shells averaged greater than 34% of concentrations found in egg shells of the hens’ counterparts producing poor quality egg shells. Immature female chickens had low (60 to 117 pg/mL) levels of circulating 1,25(OH)2 D3; concentrations were similar for immature females later classified to be either poor or good egg shell calcifiers. However, differences in 1,25(OH)2 D3 concentrations became progressively greater with age in the two groups and reached statistical significance (P Feeding 1α, hydroxycholecalciferol (1α-OH-D3) or D3 to laying hens for 22 wk resulted in significantly improved egg shell quality (∼ 7%) for those fed lα-OH-D3. No differences in egg weight, egg production, or egg mass were observed. Tibial calcification and breaking strengths were significantly improved by feeding lα-OH-D3. Hens producing eggs with superior egg shell quality have higher concentrations of circulating 1,25(OH)2 D3 than similar hens producing poor egg shells. Dietary supplementation of 1 hydroxylated vitamin D metabolites may be useful in improving egg shell quality. |
