الفهرس 
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Abstract
The present study: This investigation aimed to evaluate the effect of partial or total replacement of added DL-methionine (Met) with betaine or choline or both in diets of broilers chicks on growth performance, carcass characteristics, some blood parameters and sensory evaluation of meat and economic efficiency.The most important results: The results of the present study indicated that replacement of added methionine with betaine and/or choline positively affected final live body weight (LBW) of broiler chicks compared with their control group.The highest LBW was achieved by chicks fed T10 (50% betaine and 50% choline) and T7 (100% betaine) when compared with other dietary treatments while the lowest value was recorded with the control group. The same trend of response was observed in body weight gain (BWG) of chicks fed on diets containing different levels of betaine or choline during the whole experimental period compared with their control counterparts.Slight differences were observed among the different experimental groups of broiler chicks in feed intake FI which seemed erratic and perhaps were not related to the effect of dietary treatments.Replacing added dietary methionine with betaine and/or choline in broiler diets led to superior means of feed conversion ratio (FCR) during the three phases of growth and the whole experimental period to those attained by the control group. The obtained results revealed that replacement of added Met with BET and/or choline positively affected percentages of carcass yield,total edible parts, breast yield and deboned breast meat. While those of heart and abdominal fat were decreased but relative weights of giblets,liver and gizzard were not affected compared with their control counterparts. Inclusion of 100% betaine instead of added methionine showed significantly (P0.05) higher PI value compared with the control group. Chicks fed T10 (50% BET and 50% choline) and T7 (100% BET) had significantly higher serum concentrations of glucose, total protein, albumin and globulin when compared the other dietary treatments. On the other hand total cholesterol, triglycerides, ALT, AST, uric acid and creatinine were decreased due to dietary treatments. Acceptance of sensory evaluation was observed with treatment groups. The lowest cost/kg body weight (11.96 LE) was observed with chicks fed diets completely replaced added methionine, while the highest value in which betaine (12.91 LE) was recorded with the control group. Similar results were observed with economic efficiency.Conclusion:It could be concluded that replacing added dietary methionine by betaine,choline or both can positively affect body weight gain,feed conversion carcass yield, total edible parts,breast yield and sensory meat attributes of broiler chicks and economic efficiency of broiler production.