Efficient poultry production depends upon a number of crucial factors that include optimum nutrient digestibility, bioavailability and maximum conversion into end products like meat and egg as well as low morbidity and mortality in the flock. In the past, antibiotics were used successfully as growth promoters in poultry and animal feed to improve production performance. However, it has become increasingly apparent that many problems are associated with the use of antibiotic growth promoters (AGPs); most importantly, the emergence of increasing numbers of microbes resistant to antibiotics. Therefore, AGPs were banned in the poultry as well as in the livestock industries of many countries. Due to withdrawal of AGPs, the poultry industry faced outbreak of diseases, high mortality, compromised growth performance and thus low profitability. Researchers and producers must, therefore, seek an alternate for AGPs that provide safety both for poultry and consumer health. Many potential candidates have subsequently been put forth and evaluated to replace AGPs that include prebiotics, probiotics, phytobiotics and organic acids. These AGPs replacers showed variable degree of success depending upon nutritional, managemental and hygienic conditions. Keeping in view the importance of AGP replacers, it was the purpose of this study to the growth promoting potential of β-galacto-oligosaccharides (β-GOS), a prebiotic, and benzoic acid (BA), an organic acid, in growing broilers.
In experiment-1, 200 day old Hubbard broiler chicks, were randomly divided into four treatment groups (n = 50) with five replicates (n = 10) in each group. Birds in different treatment groups were allotted four different types of diets. Birds in the control group (β-GOS-0) were given ad-libitum corn based basal diet, free of antimicrobials and coccidiostats, whereas birds in three other experimental groups were given the same basal diets supplemented with different concentrations of β-GOS i.e., 0.1% (β-GOS-1), 0.2% (β-GOS-2) and 0.5% (β-GOS-5) for a period of 35 days. Birds in all the experimental groups were vaccinated against the Newcastle disease virus (NDV) and infectious bursal disease virus by giving primary and booster doses according to the schedule. Moreover, birds were also sensitized against 2, 4-dinitrochlorobenzene for determination of cell mediated immunity (CMI). Body weights, feed intake and feed conversion efficiency were determined on a weekly basis. At the end of experiment, ten birds from each group were slaughtered to collect blood, organs and caecal digesta for determination of serum biochemical metabolites and humoral immunity, organ characteristics and selected caecal digesta bacteria, respectively. Data were analyzed by using analysis of variance and incase of significant F-value (P < 0.05), data were subjected to Tukey's-HSD post hoc test. Results demonstrated that growth performance and feed conversion efficiency (FCE) of β-GOS supplemented birds were improved (P < 0.05) in a dose dependent manner, with the highest body weights (P < 0.05) and improved FCE (P < 0.05) observed in the β-GOS-5 group. Relative weights of liver and pancreas were higher (P < 0.05) in the β-GOS-1 group. Likewise, CMI was also higher (P < 0.05) in the β-GOS-1 group. Concentrations of caecal Lactobacilli spp. were higher in the β-GOS-2 and β-GOS-5 groups. The serum biochemical metabolites, humoral immunity in terms of antibodies titres against NDV and Clostridia spp. and coliforms were not affected by dietary supplementation of β-GOS. In conclusion, dietary supplementation of 0.5% β-GOS conferred a better response in terms of growth performance, feed conversion efficiency and caecal Lactobacilli spp. in broilers.
In experiment-2, 120 day old male Cobb broiler chicks were randomly divided into three treatment groups (n = 40) with eight replicates (n = 5) in each group. Birds in different treatment groups were allotted three different types of diets. Birds in the control group (CON) were given ad-libitum maize based basal diets, free of antimicrobials and coccidiostats, whereas birds in two other experimental groups were given the same basal diets supplemented with two different types of BA i.e., 0.096% free BA (FBA) and 0.2% slow releasing BA (SBA) for a period of 35 days. Body weights, feed intake and feed conversion efficiency were determined on a weekly basis. At the end of the experimental period, birds from each group were slaughtered to collect digesta from the crop, proventriculus, gizzard, proximal small intestine, ileum and caecum for determination of benzoic acid, microbial metabolites, microbial populations and molecular microbial ecology. Data were analyzed by using analysis of variance and incase of significant F-value (P < 0.05), data were subjected to Tukey's-HSD post hoc test. Results revealed that overall growth performance, feed intake and FCE remained unchanged among all the treatment groups. Total short chain fatty acids were only increased (P < 0.05) in the gizzard by both types of BA supplementation. Likewise, D-lactate concentration was increased (P < 0.05) by both types of BA in crop digesta, whereas, L-lactate was only increased (P < 0.05) by SBA in crop digesta. Both types of BA increased (P < 0.05) the concentrations of L-lactate, D-lactate and acetic acid in gizzard, and D-lactate in proximal small intestine. Concentrations of i-butyric acid and i-valeric acid were decreased (P < 0.05) in caecal digesta by both types of BA, whereas, n-valeric acid was only decreased (P < 0.05) by SBA supplementation in caecal digesta. Concentrations of both types of BA in different segments of gastrointestinal tract were comparable. Concentrations of gizzard Lactobacilli spp. were higher in both the BA supplemented groups, whereas, L. johnsoni and L. reuteri concentrations were higher in the SBA group compared with the control group. Similarly, in the proximal small intestine both types of BA increased the population of Lactobacilli spp., L. reuteri, L. amylovorus and Enterococci spp. Ileal concentrations of Lactobacilli spp., L. johnsoni, L. amylovorus and S. alactolyticus were higher (P < 0.05) in SBA group, whereas, L. reuteri was increased (P < 0.05) both by the FBA and SBA supplementations. Microbial populations of crop and caecum remained unchanged among all the treatment groups. Results of ileal molecular microbial ecology analysis revealed that evenness was higher (P < 0.05) in both the BA supplemented groups, whereas, the Sorensen index (P < 0.05) and the Renkonen index (< 0.5) were different only in the SBA group. However, caecal microbial ecology analysis revealed no changes among all the treatment groups. In conclusion, FBA and SBA supplementations produced similar responses in terms of microbial metabolites production with no effect on overall growth performance and feed conversion efficiency. However, SBA conferred some advantages over FBA in terms of increased bacterial concentrations, especially some species of the Lactobacilli as well as S. alactolyticus, and improved ileal molecular microbial ecology.