Abstract
Abstract: Genetically, the basis of all commercial breeds is the same. Therefore, the selection pressure for traits such as performance and carcass yield results in particular products. Genetic variation of two different broiler strains (Avian48 and Cobb500) in response to black pepper and red hot pepper supplementation was studied. Two hundred chicks from each broiler strain were randomly distributed on the following treatments, 1. Control treatment; 2. Red hot pepper treatment (0.5 %); 3. Black pepper treatment (0.5%); 4. Mixture treatment (0.25 % black pepper plus 0.25 % red pepper), these additives were added to drinking water from the first week until the fifth week of age, every group containing 50 birds distributed on five replicates (10 birds/replicate). The growth performance, carcass traits, abdominal fat, edible giblets, blood pictures, cellular immunity, and chemical blood lipid profile were estimated. Cobb500 broilers strain respond better to water supplement of red hot pepper, black pepper, and their mixture than Avian48 strain.
Moreover, adding red hot pepper (0.5), black pepper (0.5), and their mixture (0.25+0.25) to drinking water significantly improved growth performance compared to control treatments with the best results obtained from mixture supplementation. However, it's better to supplying these additives until the third week of age, especially black pepper. Using black pepper, red hot pepper, and their mixture as feed additives by 0.5% had a significant role in further improving carcass quality by lowering fat percent and blood cholesterol. LDL so decrease their percent in meat and increasing the dressing and carcass cuts as a general, with the best results reported for mixture supplement. Additionally, these herbs had the desired effect on improving broilers' cellular immunity by increasing phagocytic index and differential leukocyte count. Finally, further examinations are required to studying the response of other broiler strains and breeds to these supplements and evaluating its effect on carcass characteristics, abdominal fat, cellular immunity, blood picture, and lipid profile if used within the first three weeks of age only.

Key words: Keywords: broilers; phytogenic supplementation; Growth performance; Cellular Immunity; Abdominal Fat