Effects of dietary calcium source and quantity on the laying rate, eggshell quality, reproductive tract, liver fat level, and duodenum morphology in Dekalb white laying hens of 90 weeks of age

This study evaluated different Ca sources and levels for laying rate, eggshell quality and the reproductive tract, liver fat level, and duodenum morphology of old Dekalb White laying hens. A total of 9,900 hens were randomly assigned to one of 5 experimental diets, with 6 pens per diet and 330 laying hens per pen for 4 wk. The dietary treatments were: TRT1, positive control with hens fed a diet with 39 g/kg Ca from coarse limestone; TRT2, negative control with hens fed a diet with 36 g/kg Ca from coarse limestone; TRT3 with hens fed a diet with 39 g/kg Ca sourced from 75 % coarse plus 25 % fine limestone; TRT4, with hens fed a diet with 39 g/kg Ca from 75 % coarse limestone plus 25 % oyster shells; and TRT5, with hens fed a diet with 39 g/kg Ca from 75 % coarse limestone 25 % eggshells. Egg laying rate, BW, feather scores, and eggshell elasticity and breaking strength were similar in all treatments. Feeding eggshells to the hens (TRT5) resulted in increased duodenum villus height. Serum insulin-like growth factor-1 and serotonin levels were higher in hens from TRT3 compared to TRT5. Growth hormone receptor mRNA expression was upregulated in TRT5 in comparison to TRT1, and tight junction protein claudin-3 was downregulated in all treatments compared to TRT1. The use of eggshells as a Ca source appears to be a sustainable practice for enhancing the production performance of laying hens, possibly due to its ability to preserve intestinal morphology.