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 sourcesand levels on performance, egg quality indices, and selected blood variables oflaying hens. a total of 192 bovanz commercial layers were distributed to 6dietary treatment groups with 4 replicates and 8 birds in each replicate. theexperimental diets were iso-caloric and iso-nitrogenous, but they were differentin 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 calciumand phosphorus were different among the diets, the ratio between them was thesame in all diets. the results indicated that dietary treatments had not anysignificant effect on feed intake, feed conversion ratio, egg production, eggweight, egg mass, and body weight gain of hens. egg quality indices were notinfluenced by dietary treatments in both egg sampling, except for eggshellweight and shell weight ratio, which decreased as a reduction of the dietary calevel in the second period. the rate of broken, soft-shell and unmarketableeggs laid by the hens fed a diet containing lower ca was increased. there wasno significant effect of dietary ca source and concentration on blood ca and p,while serum alp activity decreased significantly with increasing the amountof calcium in the diet. there was also, no interaction between ca source andconcentration for any of these parameters. although all ca sources applied inthis experiment could supply the hens with sufficient ca, the rate ofunmarketable eggs decreased by using a higher concentration of ca.