Effects of eggshell calcium on productive performance, plasma calcium, bone mineralization, and gonadal characteristics in laying hens

A study was conducted with Rhode Island Red females to determine the effects of replacing limestone in the diet with ground, sterilized eggshell. Productive performance, egg quality, plasma Ca, bone characteristics, and the morphology of the ovary and oviduct were evaluated. One hundred forty-four 25-wk-old hens were housed in floor pens, located in a conventional open-sided layer shed. The birds were randomly divided into 3 groups, with each group represented by 4 replicates consisting of 12 birds each. Group 1 (control) was provided with a layer ration that contained all the CaCO₃ as fine limestone, whereas groups 2 and 3 were placed on diets in which 50 and 100% of the limestone, respectively, were substituted with ground eggshell. The birds were given free access to food and water and exposed to a 16L:8D photoperiod daily. Throughout the entire 10 wk of the study, BW, feed intake, egg production, egg weight, and egg quality of the 3 bird groups were not significantly (P > 0.05) different. Percentage of eggshell, eggshell thickness, and egg specific gravity were not affected by the treatment diets. At the end of the trial, number of ovarian follicles, ovary weight, and oviduct weight and length did not differ among hens fed the different Ca sources. The hematocrit values and concentrations of plasma Ca and P were similar in all treatment groups. Results showed that tibia-breaking strength and ash content of the birds were comparable whatever the Ca source. In addition, weight and length of the humerus, tarsometatarsus, and keel did not differ among treatments. The results indicate that eggshells can be fully used as a Ca source in layer diets without detrimental effects on productive traits, egg and eggshell quality, plasma Ca balance, bone mineralization, and gonadal performance.