عنوان مقاله [English]
Introduction Feed additives are used to promote health, improve performance and to increase nutrients efficiency in poultry feed. Antibiotics, which were used as growth promotors for years, are no longer considered as desirable additives in poultry feed, due to, their excessive or improper use, leads to accumulation of antibiotic residues in poultry products. Moreover, development of antibiotic-resistant bacterial strains in the digestive tract of food producing animals can be transmitted to the final consumer. For non-therapeutic purposes and as alternative growth promotor to antibiotics, probiotics have been introduced as suitable candidates due to their beneficial effects on poultry digestive enzymes, improve intestinal absorption, and neutralizing toxins produced by harmful microorganisms, which will result in improving the immune system and ultimately economic performance. Lactobacilli are among the most popular probiotic bacteria, because they are generally classified as safe bacteria.
Materials and methods Lactobacillus reuteri (L. reuteri ABRIG25 (MF686485)) and salivarius (L. salivarius NABRII59 (MH595987) isolated from the digestive tract of Guilan’s native chicks and Mazandaran’s duck respectively, were prepared up to 1.36×109 CFU using MRS medium at 37 ° C, under anaerobic conditions. 300 one-day-old male Arbor-Acres chicks were distributed in a completely randomized design, with 5 treatments, 4 replications(15 chicks per replicate). Experimental treatments were: 1- Basic diet as control group (Cont), 2- Basic diet + 100 g / ton Avilamycin as antibiotic group (Anti), 3- Basic diet + 200 g / ton commercial probiotic (Lacto-feed®) (Plac), 4- Basic diet + 1 g / Kg of L. salivarius NABRII59 (MH595987) bacterial powder (Pls1), and 5- basic diet + 1 g / kg of L. reuteri ABRIG25 (MF686485) bacterial powder (Plr1). Daily feed intake, weight gain, and feed conversion ratio of broilers were determined and recorded in starter, grower, and finisher periods. On day 42, two chicks were slaughtered from each replicate and the weight of internal organs and carcass cuts were recorded as a percentage of carcass weight. Chicken antibody reaction were determined using SRBS suspension. On days 22 and 35 of the rearing period, two chicks were randomly selected from each cage and 0.1 cc of SRBC solution was injected into to the wing’s vein, intravenously. Humoral immunity test was applied on days 29 and 42, using 1 cc of blood taken from the wing vein of chickens. The hemagglutination reaction was recorded based on the last two dilutions as SRBC’s antibody using the logarithm and the antibody titer against Newcastle was determined by hem agglutination inhibition (HI) test. On day 42, blood samples were taken randomly from 2 birds per replication to evaluate blood-serum parameters including glucose, cholesterol, triglyceride, HDL, LDL and VLDL. All data were analyzed using SAS software v.9.1 (2012) in GLM procedure using a completely randomized design, and comparison of statistical means was performed, using Duncan's method at the level of 0.05.
Results and discussion under the conditions of present study, native probiotic isolates (Pls1, Plr1) had a similar effect as Plac and Anti, on growth performance of chickens. No significant differences were observed between experimental treatments in terms of daily feed intake, weight gain, and feed conversion ratio. Two native probiotic isolates (Plr1, Pls1), antibiotic (Anti) and the commercial probiotics (Plac) resulted a significant reduction(P <0.05) in proventriculus weight, while no significant differences were obtained in mean relative weight of other organs. Commercial probiotic (Plac) and native Lactobacillus isolates (Plr1 and Pls1) significantly improved total immunoglobulin and immunoglobulin G (IgG) after both first and second injections (P <0.05). Lactobacillus salivarius (Pls1) Isolate, significantly improved immunoglobulin M (IgM) after the second injection. The antibody titer against Newcastle disease vaccine did not show a significant difference between treatments and control group. There were no significant differences between treatments versus control group in blood glucose, cholesterol, triglyceride, VLDL and LDL levels. Chicks fed probiotic containing diets showed no significant differences in HDL level, while it appeared with significant decrease in antibiotic treatment. Probiotics can affect gut microbiota, due to their competition in usage of nutrients and for attachment sites on the intestinal epithelial cells. Also because of antimicrobial agents’ production, they may improve the blood parameters and stimulate the immune system cells to produce cytokines which play an important role in inducing and regulating immune responses in poultry. Probiotics support lactic acid-producing bacteria and stabilize the gut microflora, which showed beneficial effects on feed conversion ratio via stimulating the production of digestive enzymes. Probiotics may reduce cholesterol synthesis through fermenting indigestible carbohydrates, leads to producing short-chain fatty acids, thereby lowering cholesterol level in the host bird.
Discrepancies in results reported by different researchers may partly be due to differences in chick’s age and breed, level of stress, diet composition, consumption period and duration, type of commercial probiotics, dose or amount of probiotic intake, management skills, and environmental conditions in different experiments.
Conclusion: The general conclusion is that the probiotic isolates used in this study are competitive with the commercial type of probiotics as well as the antibiotic used and are promising as probiotic candidate with beneficial effects on broiler’s performance, blood biochemical parameters and immune system
Keywords: : Avilamycin , Lacto-feed probiotic, Lactobacillus reuteri, Lactobacillus salivarius, Guilan’ native chick.