الفهرس 
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Abstract
The present study was conducted at the research farm of Poultry Production Department, Faculty of Agriculture (El-Shatby), Alexandria University between months of July and August, 2018. The main purpose of the current experiment is to investigate the growth-promoting effect on broilers performance and related traits response by feeding either of chlortetracycline or different levels of Sangrovit inclusion compared with those received un-supplemented diet. A total number of 450 seven days-old unsexed broiler chickens (Cobb500) were previous obtained from a commercial hatchery. Chicks were individually weighted to the nearest gram and randomly allotted into five experimental groups of 90 chicks each. Each group was subdivided into 3 replicates (30 chicks each). Birds were housed in windowed chick’s house and divided to
separate pens till the end of the trial. Each pen was equipped with manual drinkers and feeders. All chicks were kept under the same management and environmental conditions with lighting program consisted of a period of 23 h light and 1h darkness throughout the entire studied growth period and the temperature was controlled and gradually reduced from 33 to 23Cº on day 35. Experimental protocol used was in accordance with recommendations of institutional guidelines for the care. Experimental diets and water were offered ad libitum over all studied growth periods. Two experimental diets were formulated as procedure of NRC (1994) to supply similar levels of crude protein and metabolisable energy and met the requirement of broilers according to their stage of development in terms of starter period (7-21) and grower-finisher ones (21-35) day. In that, starter diet contained 23% crude protein (CP) and 3000 kcal/kg metabolizable energy (ME), whereas that of grower- finisher ones contained 21% CP and 3100 kcal/kg ME. Either of tested additives was administered through starter and grower-finisher diets, where three levels (0.5, 1.0 and 1.5 g/kg diet) of Sangrovit and one level (0.5 g/kg diet) of chlortetracycline were used until the end of experiment at day 35. Data were collected in terms of productive performance, slaughter traits, some blood metabolic and histological structure and some bacterial populations of intestine. Finally, feed cost index and relative economic efficiency were also calculated. The results obtained can be summarized as follows:
1- Feeding experimental diets included Sangrovit 0.5 g/kg up to day 35 gave the significant highest body weight and weight gain followed by those of Chlortetracycline and other levels of Sangrovit (1.0 or 1.5 g/kg diet) as compared with that of the un-supplemented diet. 712- The significant lowest feed consumed was detected with broilers received the Sangrovit inclusion level of 0.5 g/kg as compared with the other dietary treatments, whereas birds received the control diet consumed the highest amount followed by those of the chlortetracycline and 1.0 or 1.5 g/kg diet, respectively.
3- Depended on weight gain and feed consumed, feed conversion ratio was significantly improved as using dietary treatment of Sangrovit (0.5 g/kg) followed by that of the same additive at level 1.0 g/kg and chlortetracycline as compared with the other dietary treatments, respectively. The opposite was true with the control treatment which recorded the worst score.