Pre-cecal calcium digestibility of eggshell products in broilers

A broiler study was performed to determine the pre-cecal digestibility of Ca (pcdCa) of 4 eggshell products in comparison to a fine particle limestone source. Two eggshell products consisted of hatchery egg shells (HE) and 2 eggshell products consisted of consumption egg products (CE). One HE product consisted of fine particles (HE_fine) and the other HE product consisted of coarse particles (HE_coarse), while the two CE products consisted of coarse particles, with one product treated with a press (CE_press) and the other product treated with a centrifuge (CE_cen) to remove remaining egg yolk and egg white. During the first 14 d, birds received a commercial starter diet. At d 15, 360 broilers were randomly assigned to 36 pens (10 birds/pen), 6 pens per treatment. From d 15, 6 experimental diets were provided; a basal diet, a limestone supplemented diet and 4 diets containing the eggshell products. At d 23 birds were killed, after which the content of the terminal part of the ileum was sampled and pooled per pen. From three birds per pen the left tibia bone was collected for analysis of ash, P and Ca content. The pcdCa was calculated according to the World's Poultry Science Association (WPSA) protocol for determination of pre-cecal phosphorus digestibility, in this study adapted for Ca. Diets with coarse eggshell products did not differ among each other in performance, tibia characteristics and pcdCa (P > 0.05), but these characteristics were higher than for the low-Ca basal diet (P < 0.001). Pre-cecal Ca digestibility of limestone, HE_fine, HE_coarse, CE_press and CE_cen was 105, 103, 97, 95, and 96 %, respectively. The high digestibility of the supplemented Ca sources was likely due to the metabolic regulation of Ca and P absorption from the basal diet and the test products. It was concluded that pcdCa of HE is similar to CE and pcdCa of fine particle egg shells in broiler diets is similar to limestone. Use of egg shells as Ca source contributes to the circularity of food production. Furthermore, it is recommended to develop a standard protocol for determination of pcdCa.