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pp.19-26
To elucidate the effect of feeding differently prepared CaCO3 (industrially purified limestone) on laying performance, egg shell quality and serum calcium and phosphorus concentration, totally 288 layers (52 wks old), with 16 birds per replicate, 3 replicates per treatment for six treatments were employed into the series of CaCO3 treatments followed by feeding study. Six CaCO3 treatment and diet preparation includes mash diet with naturally sized CaCO3 (MNaC), mash diet with coarsely particled CaCO3 (MCoC), mash diet with finely particled CaCO3 (MFiC), pelleted diet with naturally sized CaCO3 (PNaC), pelleted diet with casein coated CaCO3 (PCnC) and pelleted diet with agar coated CaCO3 (PAgC). Hen day egg production of the bird fed both fine CaCO3 and pelleted CaCO3 were lower (p<0.05) than those fed other CaCO3 diets. Although there is no difference in average egg weight among treatments, the weight tended to be heavier once the egg production rate was low. There is no difference in feed conversion ratio (intake/egg) among treatments. Egg shell thickness was the highest (p<0.05) with feeding of MCoC whereas the value was the lowest with feeding of pelleted CaCO3 diet. Although there is some difference in egg shell thickness, the shell breaking forces were not significantly different among treatments. Calcium content of the shell was the lowest (p<0.05) in the egg from the layer fed finely particled CaCO3. Serum Ca content tended to decrease up to 8 hrs after feeding, then tended to increase afterwards. Although both agar and casein coating of CaCO3 tended to retard the recovering increase of blood Ca, the difference needed to be clarified with individual ovulation cycle. Serum P level was generally decreased as time passed after feeding. Crude protein utilizability was the highest with feeding of agar coated CaCO3 and that of fat was higher with hens fed pelleted diets. Both ash and P utilizabilities of diet with finely particled CaCO3 were the highest among treatment although there were no differences in both energy and Ca utilizabilities. Conclusively, both the particle size of CaCO3 and pelleting of CaCO3 diet could affect shell quality of the egg. The effect was more evident by the differentiation of CaCO3 particle size than any other processing such as pelleting and coating.
