الفهرس 
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Abstract
The responses of growing turkey to different dietary levels of betaine were investigated during the period from 12 to 20 weeks of age. Therefore, a basal diet was formulated to contain 21.37% CP and 3057 Kcal ME/kg. This diet was supplemented with betaine at levels of 0, 0.75, 1.5 and 2.25 g/kg diet. Thus, there were four treatment groups; each was fed to 50 birds (males and females) divided equally into two sub-groups of 25 males and 25 females in each. Results revealed that birds in T3 (1.5 g betaine/kg diet) showed the highest (P≤0.05) final LBW and total weight gain (TWG) as compared to control birds or those in other treatment groups. The superiority in final LBW of birds in T3 was associated with improvement (P≤0.05) in growth measurements including breast width and length of keel, back, shank, tibia and thigh as compared to other groups. Birds in other treatment groups (T2 and T4) did not differ significantly in growth performance parameters from that of the control birds. Males showed better (P≤0.05) growth performance parameters than females. The interaction effect between treatment x sex on all growth performance was not significant. Concentration of total proteins (TP) and albumin (AL) in blood plasma of T3 and T4 groups increased (P≤0.05) as compared to the control ones. Males showed higher (P≤0.05) concentrations of TP, AL and AL: GL ratio than females. Birds in T3 showed the highest (P≤0.05) weights of carcass, giblets, gizzard, liver and heart as well as the highest percentage of giblets. Carcass and gizzard and dressing percentages were not affected by dietary betaine treatments. Concentration of total lipids, triglycerides, LDL and HDL in blood plasma of birds was not affected significantly by feeding birds on diet containing different levels of betaine as compared to the control diet. However, only concentration of total cholesterol in blood plasma of birds showed marked reduction by feeding betaine diets, but the differences were significant (P≤0.05) with betaine supplementation at a level of 0.75 g/kg. Feeding birds on diet containing 2.25 g/kg (T4) significantly (P≤0.05) increased ALP activity as compared to the control, while did not differ significantly from birds in other betaine treatment groups. Activity of ALT, AST and ALT/AST ratio was not affected by betaine treatment, although activity of AST and ALT/AST ratio tended to increase and ALT activity tended to decrease in all betaine treatment groups as compared to the control group. Birds fed diet contained 1.5 g betaine/kg (T3) showed significantly (P≤0.05) the longest major, heaviest and longest minor muscles as well as the longest thigh, while, feeding betaine at a level of 2.25 g/kg significantly (P≤0.05) decreased thigh weight as compared to other treatments and controls. However, weight of major muscles and weight and percentage of breast meat were not affected significantly by betaine treatment. Males showed higher (P≤0.05) weights of carcass, giblets, gizzard, liver and heart. Females showed the highest (P≤0.05) giblets, gizzard and liver percentages. The interaction effect between treatment x sex on all carcass traits was not significant. Birds in T3 showed the highest economic feed efficiency (EFE %) as compared to other treatment groups. Males showed higher EFE than females. Histological examination of breast, thigh muscle and liver sections from different treatment groups showed that the intermediate level of betaine (1.5 g/kg) was the best for enhancing muscles growth (breast and thigh muscles) and liver histogeneses in turkeys.
In conclusion, growth performance parameters, body measurements, carcass traits and economic efficiency of grower turkey were improved without adversely effects on protein metabolism, lipid metabolism, enzyme activity and the histological structure of the muscles and liver by supplementing diet with betaine at level of 1.5 g/kg as compared to lower (0.75 g/kg) or higher (2.25 g/kg) betaine levels.