الفهرس 
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Abstract
The present study was carried out at the Poultry Research Farm, Faculty of Agriculture, Suez Canal University, Ismailia, Egypt. Factorial experimental design 2×2×3 was applied to evaluate the effects of crude protein and organic acids (types and levels) on physiological and productive performance of broiler chicks. A total number of 288 one day old unsexed broiler chicks (Cobb strain) were reared in wire batteries in an open house. Chicks were randomly divided into 12 treatments of 24 chicks each (3 replicate of 8 chicks). Experimental diets were composed of corn-soybean meal, in mash form. Two levels of crude protein (NRC, 1994 requirements, RPL and 2% lower, LPL) and two types of organic acids (citric; CA and fumaric; FUA) with three levels (0, 1.5 and 3% of the diet) were studied. Chicks were fed three types of diets, starter (0-3wks of age; contained 23 and 21% CP), grower (3-5wks of age; contained 20 and 18% CP) and finisher (6th wk of age; contained 18 and 16% CP). Diets were formulated to be isocaloric (3200 Kcal ME/Kg of diet). Feed and water were supplied ad-libitum during the experimental period, which lasted for 6 weeks. Physiological and productive performance parameters evaluated were growth performance, carcass characteristics, chemical analyses and physical characteristics of meat, tibia bone mineralization grade, some parameters of digestive tract, immune organs, plasma constituents and nitrogen (N) and phosphorus (P) balances.
In most cases, chicks fed RPL diet supplemented with 1.5% CA had the highest significant (P<0.01; P<0.05) productive performance figures whereas those fed LPL un-supplemented diet (0% FUA) had the worst significant figures. It could be concluded that: 1-The supplementation of organic acids (CA or FUA) was effective with the RPL. However, LPL supplemented diets tended to improve productive performance but the effects were inconsistent and insignificant. The effect of acidified diets with CA was more pronounced in the starter phase while the effect of FUA was better in the grower, finisher and total periods. 2-The nutritional/physiological protein requirements to obtain satisfactory performance of broiler chicks can be accomplished by phase feeding programs (starter, grower and finisher). 3-Cobb broiler chicks fed LPL diets supplemented with 1.5% CA reduced the N and P excretions, which has a positive effect on reducing the pollution degree of the environment by reducing P-infiltration to groundwater and N air pollution. 4-Further studies in this area are recommended using different types and concentrations of organic acids locally and commercially produced for various types of poultry (broilers, layers, turkeys, quails .......... etc).
Keywords: productive performance; broiler chickens; citric, fumaric acids and crude protein levels.