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, and 72 wk of age. Percentage shell and shell thickness (millimeters) were
determined at 22, 29, 36, 44, 50, 57, and 71 wk of age. Molt was induced at 63 wk
of age. Three commercial strains DeKalb XL-Link, ISA/Babcock B-300V, and Hy-Line W-36
were compared. There were no differences 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
uptake increased (P < .01) to 402 pmol/mg tissue per min, and percentage shell and
shell thickness increased (P < .01) to 10.23% and .389 mm, respectively. Duodenal
calcium uptake increased immediately postmolt, whereas femur ash did not increase
until 72 wk of age (P < .01).