The Effect of Supplemental Calcium and Vitamin D3 on Line and Strain Differences in Egg Shell Strength

Abstract

Lines from each of six commercial layer strains previously selected on the basis of relatively good or poor shell strength were either, (1) fed supplemental calcium as oyster shell ad libitum or (2) injected with vitamin D3 (600 I.C.U. in trial 1 and 20,000 I.C.U. in trial 2) or (3) received no supplemental calcium or vitamin D3. Shell strength was measured by shell thickness, specific gravity, deformation and breaking strength on three eggs from each bird at the beginning of the experiment and at weekly intervals for three weeks during each of two trials. Trial 1 was conducted during the twelfth month of lay and Trial 2 during the nineteenth month of lay (six months post-molt).The injection of vitamin D3 did not significantly increase the shell strength of the high and low lines, neither did it alter shell strength differences between different strains. The feeding of additional Ca in the form of oyster shell significantly improved the shell strength by all shell strength measures in Trial 1. In Trial 2, which was conducted post-molt, the shell strength was not significantly improved. Although the additional dietary Ca did not significantly alter strain and line differences in shell strength the rate of increase in shell strength of lines and in the degree of response of some strains to Ca supplementation was observed.