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Comparative use of oyster shell and limestone as sources of calcium in the diet of laying chickens 1 *2 2 2 2 Mako, A. A., Mosuro, A. O., Adedeji, B. S., Jemiseye, F. O. and Abokede, T. Department of Agricultural Science, Tai Solarin University of Education, Ijebu-Ode. Ogun State. Nigeria 2 Agricultural Biochemistry and Nutrition Unit, Department of Animal Science, University of Ibadan, Nigeria * Corresponding author: ronke.mosuro@outlook.com; 09038159961 Egg producers primarily use oyster shell or limestone as supplemental sources of dietary calcium. This study was conducted to investigate the efficiencies of limestone (CaCo ) and 3 oyster shell as calcium sources in the diets of laying hens. Ninety, 58 weeks old Golden Comet Hubbard laying birds were randomly allotted to three treatments of three replicates. Each replicate had 10 birds per replicate. Three different rations were formulated for the study. To include Diet 1 as the control, a diet with bone meal (46%) and oyster shell (54%). Diet 2 had oyster shell and bone meal supplying 82% and 18% of the dietary calcium while Diet 3 had 82% and 18% of the dietary calcium supplied by limestone and bone meal respectively. Feed and water were provided ad-libitum. The parameters measured include: Feed intake (g/d); Hen day production (%); Efficiency of feed utilization (kg); Egg and shell weight (g); Bone weight (g); Ash content of bone (%) and Calcium content of bone (%). The study lasted eight weeks. Results revealed that birds on Diet1 had the highest value for feed intake (0.11 g/d) that differed significantly (P<0.05) from the value (0.10 g/d) obtained for Diet 2 and 3 Hen day production for birds on Diet 2 (57.04) and Diet 3 (56.30) were similar, but differed significantly (P<0.05) from birds on Diet 1 (65.44). Efficiency of feed utilization (EFU kg) was not significantly affected by the dietary treatments as birds on Diet1 had the lowest EFU value (1.80) while birds on Diet 2 had the highest EFU value (2.05). A higher percent of eggs within 50-59g were laid by birds on Diet 3, while eggs of 60g and above were laid by birds on Diet 1 (62 g), significant (p<0.05) variations occurred among treatment means for these egg grade. Egg shell percent was not significant, same trend was observed for bone weight. The effect of dietary treatment on the ash content of bones were similar for birds on Diet 2 and 3, except for bone humerus, however, significant (p<0.05) variation occurred between birds on diets 1 and other two Diets. Calcium contents of the different bones were differed significantly (p<0.05) with birds on diet 3 recording the highest values for all bone investigated. It can be concluded from this study that Limestone can replace oyster shell as a source of calcium in the diet of laying hens without deleterious effect. Introduction Laying hens have high demand for calcium, especially during peak egg production when calcium output is at its greatest. Calcium is essential for egg formation as the medullary bone is a woven bone that acts as a labile source of calcium for eggshell formation (Whitehead, 2004).