EFFECT OF DIETARY CALCIUM LEVEL ON MEDULLARY BONE CALCIUM RESERVES AND SHELL WEIGHT OF LEGHORN HENS

Two experiments were conducted to determine the effect of different levels of dietary Ca and subsequent feeding of a very low level of Ca on the medullary bone Ca reserves of laying hens. In Experiment 1, a total of 30 40-wk-old Single Comb White Leghorn hens were offered a diet with 2.5,3.5, or 4.5% Ca for a period of 21 days with 10 birds per dietary treatment. On Day 21, five hens from each dietary treatment were euthanatized. The remaining birds were offered a .46% Ca diet for 5 days. In Experiment 2, 25 Single Comb White Leghorn hens were fed a 3.5% Ca diet for 21 days. Hens were then offered a .46% Ca diet and five hens euthanatized on Days 0, 2, 3, 5, and 7 of feeding the low-Ca diet. In Experiment 1, dietary Ca level had a significant (P < .05) effect on total medullary Ca reserves of laving hens. Previous dietary Ca level had no significant (P > .05) effect upon medullary bone Ca reserves after subsequently feeding the low-Ca diet for 5 days. There was a (P < .05) significant reduction in medullary bone Ca reserves of hens, regardless of previous level of calcium fed. In Experiment 2, feeding a low level of dietary Ca resulted in a significant (P < .01) reduction in medullary bone Ca reserves of all bones measured, except the humerus. Although there was a significant (P < .05) reduction in medullary bone Ca during the depletion period, hens appeared to make some attempt to conserve medullary bone Ca reserves.