The experiment was to study the effect of different levels of probiotics (Bioplus-2B) and calcium carbonate on relative weight of the internal organs, digestive pH and body weight in laying hens. This experiment was performed with 144 pieces of chicken strains HY-LINE (W 36) at the age of 58 to 68 weeks for 6 treatments 6 replicates (each replicate with 4 pieces of chicken) in the form of randomized complete block design with factorial treatment arrangement 3 x 2 consists of three physical form calcium carbonate (flour, granulated and a mixture of both) and two levels of probiotics (0, 0.04 percent) for 11 weeks (one week adaptation period). The interaction between probiotics and calcium carbonate and also the main effect of calcium carbonate had no significant effect on the digestive PH (P 0/05).but the main effect of probiotic caused the significant of reduction in PH these parts especially the crop and gizzard(P 0/05). The relative weight of the digestive system including liver weight, ovarian weight, oviduct weight and body weight were not affected with main effect of calcium carbonate and probiotic and also interactions between the two (P 0/05). The results showed that probiotics can reduce digestive PH and lead to reduced populations of pathogenic microorganisms and ultimately increase the solubility and absorption of some nutrients such as calcium and magnesium and have positive or negative effect on some internal organs of the chicken body means that cause increase or decrease in these organs

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