Efficacy of Feeding Various Calcium Source and Concentration on Egg Quality, Some Blood Variables, and Performance of Aged Laying Hens

The primary aim of this study was to assay the influence of dietary Ca sources and levels on performance, egg quality indices, and selected blood variables of laying hens. A total of 192 Bovanz commercial layers were distributed to 6 dietary treatment groups with 4 replicates and 8 birds in each replicate. The experimental diets were iso-caloric and iso-nitrogenous, but they were different in the concentrations of available phosphorus and total calcium (0.29 and 3.8% or 0.31 and 4.0%, respectively) and in the origination of applied calcium (limestone A, limestone B, and oyster shell). Although the amounts of calcium and phosphorus were different among the diets, the ratio between them was the same in all diets. The results indicated that dietary treatments had not any significant effect on feed intake, feed conversion ratio, egg production, egg weight, egg mass, and body weight gain of hens. Egg quality indices were not influenced by dietary treatments in both egg sampling, except for eggshell weight and shell weight ratio, which decreased as a reduction of the dietary Ca level in the second period. The rate of broken, soft-shell and unmarketable eggs laid by the hens fed a diet containing lower Ca was increased. There was no significant effect of dietary Ca source and concentration on blood Ca and P, while serum ALP activity decreased significantly with increasing the amount of calcium in the diet. There was also, no interaction between Ca source and concentration for any of these parameters. Although all Ca sources applied in this experiment could supply the hens with sufficient Ca, the rate of unmarketable eggs decreased by using a higher concentration of Ca.