الفهرس 
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Abstract
The primary goal of the livestock producer is the increase of the Efficiency of animal protein production. Consumer performance for m6re lean and less tat in beef has focused attention on genetic and nutritional factors influencing the animal performance. The lack of sufficient feeds to meet the nutritional requirements of animal population is one of the most critical problems of beef production in Egypt. Both overfeeding and underfeeding are against the economy of meat production process. The basic biology of all cattle is similar, but differences in mature size and rate of maturing have a marked influence on application of basic nutrition principles to the wide range of environmental and management conditions of practice. For this reason, the animal size and rate of body gain of exported cattle has been considered in calculating nutrient requirements. The non-protein nitrogen source most commonly fed to ruminant animals is urea, Urea is rapidly hydrolyzed to ammonia in the rumen and excessive am0unts of absorbed ammonia can prove toxic to the ruminant animal. Proper management procedures are necessary when non-protein
nitrogen is fed both to prevent ammonia toxicity anclto avoid reduction in feed intake, Toxicity can be avoided by thoroughly mixing urea with the diet and setting the maximum concentration at one percent of the diet dry matter. urea is used more completely when low-protein diets are fed. As agriculturists the world over increase their efforts to expand crop and animal production, numerous mineral materials are receiving greater attention as dietary supplements in animal husbandry. One Soup of minerals stands out among the rest and its exciting bag of physical and chemical tricks promises to contribute to many areas of animal production in the last time. This group is the soil minerals such as zeolite, bentoninte and clay. Therefore the present study was designed to determine the effect of different dietary protein level, protein sources and clay supplementation and their interactions on growth performance. feed efficiency, profit analysis, blood constituents and slaughter traits in the growing exported Holstein calves under Egyptian conditions.