الفهرس 
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Abstract
Two experiments (40 d each) were conducted to study the performance of broilers in response to some feed additives. Experiment I was conducted to study the effect of probiotic on performance, intestinal bacterial count, histopathological picture, immunity and some blood constituents in broilers. A total of 900 day-old broiler chicks (Cobb 500 strain) were randomly assigned into two experimental groups, each group was subdivided into six replicates (75 birds each). Birds of group I served as control, and given the basal diet. Birds of group II were fed the basal and fortified with 500g I ton Clostat” (2 xlO 7 CFU Ig). The probiotic-supplemented group showed better (P 0.05) BW , BW gain, FCR and higher European Production Efficiency Index compared to the birds in the control group. Although the probiotic-supplemented group showed higher (P < 0.05) dressing percent. There are no significance differences (P > 0.05) between groups in the all serum parameters except for total serum protein was higher in probiotic-supplemented group. However, there was a significant increase (P < 0.05) in lymphocyte count as well as ND antibody titer in probiotic-supplemented birds. Bacteriological analysis for fecal samples revealed a significant reduction (P < 0.05) in total aerobic bacteria and Clostridium perfringens count as well as significant reduction (P < 0.05) in Clostridium perfringens isolation percent in probiotic-supplemented group. The histopathological examination revealed the more healthier status of
birds received the supplemented probiotic. Results suggest that, B. subtilis PB6 probiotic has an antibacterial action toward C. perfringens and has a growth promotion and immunostimulant effects and can strongly control necrotic enteritis as an antibiotic saver. Experiment II was conducted to study the effect of a natural absorption enhancer (Lysoforte Booster on performance, metabolic profile and carcass traits in broiler.996, day old chicks (Cobb 500 ) were weighed and randomly assigned into 4 groups, each of 3 replicates (83 birds per pen ). Group I (negative control) was fed the basal diet which was lower in oil and synthetic amino acids (L-Lysine and DL- Methionine). Group II (positive control) was fed the basal diet recommended by the breed catalogue. Group III was fed the negative control diets plus 250 g Lysoforte Booster ® per ton of feed. Group IV was fed the negative control diet plus 500 g Lysoforte Booster ® per ton of feed. Feeding the negative control diets resulted in poorer (P < 0.05) BW , poorer (P < 0.05) BW gain and poorer (P < 0.05) FCR in comparison with birds of the positive control group and birds fed the 2 levels of Lysoforte Booster ®. However, no significant differences were detected in the same parameters among other groups (positive control group or the negative control groups supplemented with the 2 levels of Lysoforte Booster ® ). The negative control group had a significantly (P < 0.05) lower dressing percent, however there were no significant differences (P > 0.05) in the other carcass traits. There were no significant differences (P >
0.05) between all groups in all serum parameters. Results revealed that feeding the emulsifier (Lysoforte Booster®) at a rate of 250 gm! ton has improved growth performance in broilers as a consequence of improved nutrient absorption. It also resulted in higher European Production Efficiency Index. It could be concluded that, away from the antibiotic growth promoters feed additives, the direct fed microbials and the natural feed emulsifiers ( absorption enhancer) could be added to broilers diets to maximize performance and improve the economics of the production. (Key words: broiler, probiotic,immunity, necrotic enteritis,absorption enhancer, energy, amino acids, performance).