effect of different supplements on eggshell quality, some characteristics of gastrointestinal tract and performance of laying hens

this study was performed to investigate the effects of antibiotic, organic acid, probiotic and prebiotic supplementation on performance, egg shell quality, ph value of gastrointestinal (gi) tract and small intestinal morphology of laying hens. the experiment was a completely randomized design with 160 laying hens strain (w-36) from 32 to 42 weeks of age, with five treatments, four replicates and eight hens in each replicate. the experimental treatments consisted of: 1-basal diet, 2-basal diet + 150 g per ton antibiotic (oxytetracycline), 3-basal diet + 3 kg per ton mixture of organic acids supplementation, 4- basal diet + 50 g per ton probiotic (protoxin) and 5-basal diet + 2 kg per ton prebiotic (mannan oligosaccharide). during the experimental period, performance characteristics were evaluated. at the end of experiment two birds per replicate was sacrificed for small intestinal morphology. the results showed that organic acid and mannan oligosaccharide significantly increased average egg weight. also feed conversion ratio significantly improved by mannan oligosaccharide. eggshell quality was not significantly affected by dietary treatments. regarding gastrointestinal tract characteristics, ph value of different parts of gi tract were significantly affected by dietary treatments. villi height in duodenum by probiotic and in ileum by mannan oligosaccharide significantly increased. villi width in duodenum by antibiotic and probiotic and in ileum by mannan oligosaccharide significantly increased. the number of goblet cells in duodenum by addition of antibiotic and in ileum by mannan oligosaccharide significantly increased. it was concluded that the use of organic acids and mannan oligosaccharide could have positive effects on performance of laying hens.