Particle size of oyster shell meal and calcium: phosphorus ratios in broiler diets

: The effects of Ca:P total ratio and particle size of oyster shell meal (OSM) were evaluated in broiler diets. In Experiment 1, 800 broilers (22-42 days old) were distributed in a 2×2 factorial design, with two Ca:P ratios (1.7 and 2.0:1) and two OSM particle sizes (coarse = 1,354 µm and fine = 428 µm), totaling four treatments with 10 repetitions with 20 broilers. Feed intake, weight gain, and feed conversion ratio were calculated. In Experiment 2, 1,280 broilers were distributed in a 2×2×2 factorial design (1.7 and 2.0:1 Ca:P ratios; coarse and fine OSM; male and female broilers), with eight treatments and 16 repetitions with 10 broilers. Apparent metabolizability of dry matter, Ca, P, and apparent metabolizable energy (AME), as well as bone resistance, bone weight, ash, Ca, and P content in the tibia were assessed. Growth performance was not affected (P > 0.05). Coarse OSM increased tibia Ca content in male broilers (P < 0.001), and higher Ca:P ratio improved bone ash and bone resistance in both sexes (P < 0.001), but reduced P content in male broilers (P < 0.05); male broilers displayed heavier bones with higher ash content than females (P < 0.05). Metabolizability of Ca was improved with coarse OSM (P < 0.05); whereas metabolizability of DM, P, and AME was not affected (P > 0.05). In conclusion, diets with a Ca:P total ratio of 2.0:1 containing coarser OSM improved bone mineral composition, particularly in male broilers, and coarse OSM improved the metabolizability of Ca in broilers regardless of the Ca:P total ratio or broiler sex.