الفهرس 
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Abstract
Ninety day one old Cobb chicks were employed to investigate the effects of different levels of dietary crude protein (CP) in long-term isocaloric diets on the development of the digestive organs in broilers, villous morphology, immune status, in addition to the localization and distribution of cholecystokinin hormone in the digestive organs was determined
Chicks were randomly allotted to three treatments and fed three diets containing CP 20%, 22 % and 24 % in starter and 17% 19% 21% in finisher respectively.
At the end of the experiment (42 days), six chicks of each treatment were slaughtered samples were taken from esophagus, crop, proventriculus, gizzard, duodenum, jejunum, small intestine, large intestine and pancreas and fixed in 4% paraformaldehyede and stained using ordinary stain (H&E) and special stains (PAS, Alcian Blue, Fontana Masson’s, Churukian-Shenck and Toluidine blue) as well as the peroxidase-antiperoxidase technique to determine the ontogeny and distribution of cholecystokinin immunoreactive cells on gastrointestinal tract.
Results showed that broiler performance with respect to feed intake, weight
gain, feed to gain ratio and water intake were not significantly influenced by CP regimens (p>0.05) as the average body weight in the LP group was 2.3Kg, 1.8 Kg in the NP group and 2,4 Kg in the HP group. Furthermore, CP regimens did not significantly influence broilers liveability and feed cost (p>0.05).
For Light Microscope (LM) and morphological analysis, the results showed that dietary CP significantly affected the mucosa and tunica muscularis of the esophagus and the crop, the proventricular plicae and glands, villous height, crypt depth, intraepithelial lymphocytes (IELs), enteroendocrine cells (EECs) and goblet cells (GCs) count, whereas the esophagus, gizzard and recto-colon did not suffered from any variation in their layers as a results of dietary protein change.