الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The present study was carried out to study the effects of feeding low crude protein diets with maintaining optimal levels of essential amino acids and threonine supplementation (above the recommended levels). Effect of feeding ideal protein diets (formulated according to digestible amino acids) was evaluated as well in the starter, grower and finisher diets of broiler chickens on growth performance (body weight, body gain, feed intake, feed conversion ratio and protein efficiency ratio), carcass quality, serum metabolites (total protein, albumin, uric acid and creatinine) and excreta characteristics. Effects on Haemagglutination inhibition titer against NDV, immune organs index and histopathological changes of some immune organs, intestine, liver, kidney and heart were another objective of the study.The results of the study revealed that: Body weight and body weight gain of the broiler chickens fed low protein diets (2% less than the recommended levels) and supplemented with 120 or 140% of Thr requirements were significantly lower than that of the broiler chickens fed the control diets (basal diets).Body weight and body weight gain of the broiler chickens fed low protein diets (-1%) with Thr supplementation or ideal protein diets (based upon digestible AA requirements) were not significantly different from that of the broiler chickens fed the control diets (basal diets). Feed consumption of the broiler chickens fed the low protein diets (-2%) and supplemented with Thr was significantly decreased compared to that of the broiler chickens fed the control diets. Decreasing dietary CP by 1% with supplementation of Thr maintained feed consumption near to that of the broilers fed the control or ideal protein diets. Feed conversion ratios (FCR) of the broiler chickens fed diets containing low CP by 2% and Thr supplemented were higher than those of the other treatments. FCR of the broiler chickens fed diets containing low CP (-1%) and supplemented with Thr and those fed ideal protein diets were not significantly different from those of the broiler chickens fed control diets containing recommended protein and Thr levels. Decreasing dietary protein by either 1 or 2% with Thr supplementation (120 or 140% of the requirements) has no effect on abdominal fat but significantly increased liver weight. Chickens fed low CP (-2%) with Thr supplementation have higher bursa weight and lower spleen weight than broilers fed ideal protein or control diets. Feeding the broiler chickens low protein diets (-2%) with Thr supplementation significantly decreased the serum total protein, albumin and globulin levels, while increased serum uric acid level with no effect on serum creatinine level. Chickens fed ideal protein diets and also those fed on low dietary CP (-1%) with Thr supplementation have significantly lower serum uric acid than the chickens fed the control diets. The broiler chickens fed ideal protein diets had higher HI titer value compared to broiler chickens fed low protein diets and also higher than the chickens fed the control diets. While the lowest HI titer observed with the chickens fed low CP (-2%) and Thr supplemented diets. So feeding the ideal protein diets improved immune response as the chickens fed on ideal protein diets had the highest spleen weight % (primary immune response organ), higher HI titer and normal lymphoid aggregations with histopathological examination.Feeding the broiler chickens low protein diets and ideal protein diets resulted in increase acidity and moisture content of excreta but decreased nitrogen% of excreta.Generally, it could be concluded that the dietary protein level could be decreased by 1% of the recommended levels with supplementation of Thr (120 or 140% of the recommended levels) without adverse effects on body weight, body weight gain, FCR, serum metabolites and immune response. As well as formulating broilers diets based upon the digestible essential amino acids (Ideal protein diets) can be used to maintain optimal broilers production. In addition, feeding LCP-diets with proper AA could reduce nitrogen emission and so environmental pollution.