الفهرس 
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Abstract
This work was carried out at Nutrition and Veterinary Clinical nutrition department, Faculty of Veterinary Medicine, Alexandria University to investigate the effect of vitamin B12 or biotin supplementation without or with bile salt on change in body weight, production performance, egg quality, immune response, some blood parameters and carcass quality of Lohman laying hens. Two hundred seventy Lohman of 53 weeks old of laying hens obtained from a local trade Company. The hens were weighted separately and randomly allotted into 6 separate groups (45 laying hens per each group), each group subdivided into three replicates (15 hens per replicate). The laying hens were fed a basal diet containing 17% crude protein. group one fed on the basal diet without supplement and consider as control, while group 2 and 3 fed on the basal supplemented by 0.02 ppm of vitamin B12 or 0.3mg biotin/kg diet respectively, while group 4-6 fed as previous three groups with 400 g of bile acid/tone diet. All the experimental diets and fresh water were available throughout experimental periods (8 weeks). The obtained results are summarized in the following:
• It was observed that dried bile acid supplementation (DBA) alone or with vitamin B12 or biotin reduced weight loss of laying hens throughout the whole experimental periods by about 11.2%, 39.4% and 48.8% respectively when compared with laying hens group fed the same ration without DBA supplementation.
• Vitamin B12 or biotin supplementation without or with DBA addition slightly decreased egg weight compared with control.
• Vitamin B12 supplementation non significantly (P≥0.05) increased average egg production% throughout the whole experimental period by about 6.4%, while biotin reduced egg production% compared with control group. Moreover, DBA without or with vitamin B12 supplementation non significantly (P≥0.05) increased average egg production% throughout the whole experimental period by about 2.5% and 5.9% respectively while, DBA with biotin supplementation significantly (P˂0.05) increased average egg production% throughout the whole experimental period by about 8.4% compared with laying hens group fed on the same diet without DBA addition.
• It was observed that vitamin B12 or biotin supplementation in laying hens diet significantly (P˂0.05) increased average daily feed intake by about 3.0% and 14.6% respectively compared with control, while DBA addition increased average feed intake of laying hens.
• Vitamin B12 or biotin supplementation alone or with DBA addition improve average FCR throughout whole experimental period compared with control, while DBA addition deteriorate FCR compared with control.
• Vitamin B12 or DBA supplementation non significantly improved egg shell weight and relative weight compared with control, while Biotin addition had no clear effect.
• Vitamin B12 or biotin supplementation non significantly reduced yolk weight and relative weight improved albumen weight compared with control, while DBA without or with vitamin B12 or biotin supplement improved yolk weight and relative weight while reduced yolk index compared with laying hens group fed on the same diet without DBA addition.
• Dried bile acid supplementation (DBA) alone or with vitamin B12 or biotin non significantly decreased egg cholesterol and triglycerides contents than the group fed Vitamin B12, biotin or control group.
• All treatment improved WBCs, RBCs count, Hb% and PCV% of laying hens compared with control.
• DBA addition without or with vitamin B12 or biotin supplementation had no significant effect on serum glucose and total protein concentrations, while non significantly reduced serum albumin and increased globulin concentration compared with control.
• It was observed that vitamin B12 or biotin supplementation non significantly (P≥0.05) reduced blood serum triglycerides, total cholesterol and LDL concentrations while numerically increased HDL concentrations compared with control. Also, DBA addition without or with vitamin B12 or biotin supplementation non significantly (P≥0.05) reduced blood serum triglycerides, total cholesterol and LDL concentrations while numerically increased HDL concentrations compared with laying hens group fed on the same diet without DBA addition.
• It was observed that, vitamin B12 or biotin or dried bile acids supplementation in laying hens diet had no clear effect on serum uric acid and creatinine concentrations while, non significantly increased serum GOT and GPT activities compared with control.
• It was observed that vitamin B12, biotin or dried bile acids supplementation in laying hens diet improved antibody production against New castle disease vaccine and non significantly increased phagocytic activity and index compared with control.
• Vitamin B12 or biotin supplementation in laying hens diet significantly (P˂0.05) increased neutrophil% compared with control. Moreover, it was observed that DBA addition without or with vitamin B12 or biotin supplementation significantly (P˂0.05) increased neutrophil% compared with laying hens group fed on the same diet without DBA addition.
• It was observed that, vitamin B12 or biotin or dried bile acids supplementation non significantly (P≥0.05) improved ether extract digestibility of laying hens compared with control.
• It was found that vitamin B12 or biotin supplementation without DBA addition non significantly decreased liver tissue fat% on dry matter or fresh basis by about (10.4% and 19.5%) and (22.8% and 25.4%) respectively compared with control. Moreover, it was observed that DBA addition without or with vitamin B12 supplementation non significantly (P≥0.05) reduced hepatic lipid content on dry matter or fresh basis by about (10.1% and 6.5%), (5.6% and 4.3%) respectively compared with laying hens group fed on the same diet without DBA addition.
• It was observed that, vitamin B12, biotin or DBA supplementation in laying hens diet markedly decrease the pathological vacuolation and showed nearly normal hepatocytes. Moreover, all treated groups showed decreased fatty changes of hepatic tissues.
• It was observed that, vitamin B12, biotin or DBA supplementation in laying hens diet had no significant effect on carcass traits. However, treated groups exhibited non significant increase of gizzard and spleen relative weights.
• It was observed that vitamin B12 or biotin supplementation in laying hens diet increased duodenal and ileum muscular thickness, villi length, villi width and crypt depth compared with control. Moreover, DBA addition in laying hens diet without or with vitamin B12 or biotin supplementation improved duodenal and ileum muscular thickness, villi length, villi width and crypt depth compared with laying hens group fed on the same diet without DBA addition.