DUODENAL CALCIUM-UPTAKE, FEMUR ASH, AND EGGSHELL QUALITY DECLINE WITHAGE AND INCREASE FOLLOWING MOLT

An experiment was conducted to test the hypothesis that the decline in eggshell quality over time during egg production, and its improvement after molting, paralleled the rate of calcium uptake by the duodenum of the laying hen. In vitro duodenal calcium uptake rate and femur ash (percentage of femur weight) were determined at 37, 45, 51, 58, 68, a nd 72 wk of age. Percentage shell and shell thickness (millimeters) we re determined at 22, 29, 36, 44, 50, 57, and 71 wk of age. Molt was in duced at 63 wk of age. Three commercial strains DeKalb(R) XL-Link, ISA /Babcock(R) B-300V, and Hy-Line(R) W-36 were compared. There were no d ifferences in duodenal calcium uptake rate among strains. There was a significant decline (P < .01) in duodenal calcium uptake from 408 pmol /mg tissue per min at 37 wk of age to 329 pmol/mg per min at 58 wk of age. Femur ash decreased (P < .01) from 50.8% at 37 wk of age to 47.6% at 58 wk of age. Percentage shell and shell thickness declined (P < . 01) from 9.79% and .403 mm at 22 wk of age to 8.88% and .373 mm at 57 wk of age, respectively. After the induced molt, duodenal calcium upta ke increased (P < .01) to 402 pmol/mg tissue per min, and percentage s hell and shell thickness increased (P < .01) to 10.23% and .389 mm, re spectively. Duodenal calcium uptake increased immediately postmolt, wh ereas femur ash did not increase until 72 wk of age (P < .01).