This study was undertaken to asses the energetic efficiency of calories provided by different fat sources and levels in Avian broiler chick diets, either on isocaloric or excess energy basis. Therefore, nine isocaloric-isonitrogenous diets were formulated. The control (corn-soybean diet) contained no added fat, while sunflower oil, palm oil, dry fat (Ultrakcal dry) or soy lecithin were incorporated into the other eight diets at the expense of energy provided by yellow corn at 2.5% or 5% of the diet. Four more diets having excess ME were obtained by adding each of these fat sources to the control diet at 2.5%. Each diet was fed to four replicates of seven chicks each, during the starting and growing period until 42 days of age. The obtained results could be summarized as follows: 1-Regardless of supplemental fat level, dry fat (Ultrakcal dry) was used less efficiently by chicks compared with the other fat types tested. 2-Sunflower oil, palm oil or soy lecithin can be economically used and included at 2.5 or 5% of chicks diet with no adverse effect on their performance for weight gain and feed conversion. 3-Further improvement in the performance of chicks for weight gain and feed conversion was achieved when each of the different types of fat was added to the control diet at 2.5% as an additional energy source. 4-Ether extract digestibility was enhanced, while that of crude protein, crude fiber and NFE was reduced upon feeding the fat-containing diets. 5-Regardless of dietary fat source, the level of dietary fat in isocaloric -isonitrogenous diets had no effect on dressing percentage, but abdominal plus visceral fat in chicks carcass was increased due to dietary inclusion of fat. Moreover, increasing of the ME content of the control diet by additional fat produced carcasses of higher dressing percentage and more depot fat. 6-Feeding fat-containing diets decreased the moisture and protein contents and concomitantly increased the lipid content in chicks meat. 7-Neither dietary fat source nor its level affected the chicks-meat pH value. However, values of water holding capacity and tenderness of chicks meat were decreased , and color score was increased upon feeding the fat-containing diets. 8-Neither dietary fat source nor its level affected total proteins in the plasma of chicks. On the other hand, concentrations of plasma total lipids, triglycerides and cholesterol were increased concurrently with increasing the dietary fat level.

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The influence of dietary protein levels and two types of pro-nutrients e.g. enzyme mixture containing phytase or probiotics on growth performance, carcass characteristics, meat quality and plasma biochemical constituents of broiler chicks was studied herein as means of improving protein utilization and decreasing feed cost. A complete randomized factorial design was conducted including two levels of crude protein 22 and 20% CP in the starting and 20 and 18% CP in the growingfinishing periods. Each CP level was fed either without or with enzyme mixture containing phytase or probiotics. Thus, there were 6 dietary experimental treatments, each one was fed to 24 one d-old unsexed broiler chicks divided equally among four replicates of 6 chicks each housed in a battery (30×35×40 cm). At the end of the experiment, 3 chicks of each treatment were slaughtered to determine carcass characteristics and meat quality traits. Furthermore, four plasma blood samples of each treatment were collected to determine some biochemical constituents. Also, nutrients digestibility and economic efficiency of treatments were also calculated.Increasing protein level significantly increased growth, decreased feed intake thus improved feed conversion ratio (FCR), protein conversion ratio (PCR) and economic efficiency. Pro-nutrients supplementation significantly increased growth, decreased feed intake and improved FCR, PCR and economic efficiency, with probiotics being more efficiently than enzyme mixture containing phytase, and this was clear in each protein level. Enzyme mixture containing phytase or probiotics significantly improved digestibility of dry matter and crude fibre. Increasing protein level significantly increased front part and decreased hind part, meanwhile protein level and /or pro-nutrients did not significantly affect chemical composition and physical characteristics of meat.Enzyme mixture containing phytase increased plasma Ca and inorganic phosphorus (iP), the later was significantly increased by probiotics supplementation, too. Plasma ALT was significantly decreased due to probiotics supplementation, showing the improvement in liver functions.In conclusion, low crude protein diet e.g. 20 and 18% in the starter and growerfinisher diets, respectively could be fed to broiler chicks when supplemented with probiotics cocktail containing Bacillus subtillis fermentation extract, Brewers yeast extract, lactic acid, citric acid, calcium propionate, sodium aluminosilicate and DLmethionine without adverse effects on growth performance and carcass quality, moreover it improved economic efficiency.