Abstract
Six experiments were conducted to investigate the effect of probiotics, prebiotics and synbiotics for the improvement of productive performance, intestinal microbial balance, intestinal histomorphology, immune response and cost-effectiveness of broiler chickens. Suitability of the above mentioned feed additives as alternative to antibiotic growth promoters were also examined. A total of two thousand four hundred and eighty Cobb-500 one-day-old straight run broiler chicks were allotted to 6 independent feeding trials to achieve objectives stated in the study. Growth performance and meat yield characteristics of the experimental birds were studied in first two experiments, while the bacteriological, immunological and histological observations were focused in remaining experiments. Antibiotic Growth Promoter (AGP), (Lincomycin 2.2%), probiotics prepared from spore forming bacteria and yeast products, prebiotics and synbiotics were used as alternatives to antibiotics. Productive performance and meat yield characteristics of broiler, microbial, immunological and histological observations of their intestine were performed at experimental farms and Laboratories. Chemical analysis of complete experimental diets (both starter and grower phase) were performed in Degussa Laboratory, Germany (Courtesy of Evonik Degussa GmbH). The results of experiment 1, 2, 3 and 6 revealed that broiler chickens received probiotics and synbiotics showed significantly higher live weight gain (4.5-11%) and lower feed conversion ratio (0.03 to 0.2 decimal) than the birds received AGP. Feeding yeast cultured Saccharomyces cerevisiae containing probiotics (20g/100kg of mixed feed) and prebiotics (50g/100kg of mixed feed) did not improve live weight gain and FCR compared to the birds fed AGP (15g/100kg of mixed feed). In experiment-1, feeding probiotics (DSM 50g/100kg of mixed feed) increased dressing percentage of birds compared to the AGP treated group. Abdominal fat contents were remarkably reduced in the birds received probiotics. Overall, probiotics incorporated birds were able to show superior performance and reduced mortality than that of AGP. The total viable count in intestinal samples was significantly increased (P<0.01) and total E. coli count was decreased after inclusion of AGP and PB or their combination. Almost similar results were found when prebiotics or synbiotics were supplemented in the diets. Overall histomorphology of the intestine in experimental birds were significantly improved after supplementation of different test ingredients. The TEC of duodenum, ileum or caecum were significantly decreased (P<0.01) in all supplemented groups. Villi length was significantly (P<0.01) increased in the broilers fed probiotics, AGP or combination of both or prebiotics or synbiotics. Villi length of duodenum, ileum and caecum was taller and crypt depth of duodenum, ileum and caecum was shorter in broilers fed synbiotics. In all experiments, antibody titres against ND and IBD were significantly (P<0.01) increased in either probiotics or AGP or combination of both or prebiotics or combination of prebiotics and AGP compared to the control. Results of economic analyses also confirmed the benefits of inclusion of probiotics, prebiotics or synbiotics in the diets of broiler chickens. Based on the results, it may be concluded that the natural growth promoters (probiotics, prebiotics or synbiotics) may be recommended for safe and quality broiler meat production.