Evaluation of the use of probiotics in diets with or without growth promoters for broiler chicks

This work was carried out to evaluate the use of Bacillus subtilis probiotic C-3102 (1010cfu/g) in diets with or without growth promoters on the performance of broilers in the period from 1 to 42 days of age. It was used 1,200 Cobb line broilers, distributed in a complete randomized block with five diets: negative controller (without promoters); Bacillus subtilis (30 g/t ration); Bacillus subtilis (50 g/t ration); Bacillus subtilis (30 g/t ration) + colistin (10 ppm); avilamycin (10 ppm) + colistin (10 ppm). Each diet was evaluated in 10 repetitions with 24 birds. From 21 to 42 days of age, feed intake, weight gain and feed conversion were evaluated, and at 42 days of age, productive efficiency index was evaluated. At the end of the experimental period, it was observed an increase in the consumption of diet with the lowest dose of Bacillus subtilis (30 g) in relation to that one with Bacillus subtillis (30 g) + colistin (10 ppm). The values of weight gain obtained with the diet with the lowest dose of Bacillus subtillis (30 g) and with avilamycin (10 ppm) + colistine (10 ppm) were higher than those of the birds fed control diet (without promoters). For feed conversion, the best results were obtained by supplying diets containing 50 g of Bacillus subtillis, diet with 30 g of Bacillus subtillis + 10 ppm of colistin; and diet with 10 ppm of avilamycin + 10 ppm colistin. For the analysis of productive efficiency index, the best results were obtained with diets containing additives (probiotics and/or antibiotics) in comparison to the control diet. Bacillus subtillis C-3102 probiotic, at concentration 1010 cfu/g, is an efficient substitute of antibiotics.


Introduction
The use of antibiotics as growth promoter has been a common practice in poultry production since the 1950s (Dibner & Richards, 2005).These compounds may improve animal performance by excluding microorganisms which compete with them for food nutrients in the gastrointestinal tract (Macari & Furlan, 2005), and by favoring the R. Bras.Zootec., v.39, n.12, p.2687-2690, 2010 microorganisms considered as beneficial (Flemming & Freitas, 2005).However, the indiscriminate use of antibiotic growth promoters (AGP) led to emergence of resistance in pathogenic bacteria, and as result, the European Union has banned the addition of several antibiotics in broiler feeds since 2006, and other countries should follow this trend soon (Palermo, 2006).
Considering the inevitable ban of AGP, and aiming at maintaining the productivity levels achieved by modern poultry production, research has been developed to find efficient alternatives to the use of AGPs (Rostagno et al., 2003).In this context, microbial products, such as probiotics, may be one of such alternatives.
Probiotics are defined as a feed supplement composed of live microorganisms that benefit their host by balancing its intestinal microbiota (Fuller, 1989).Their mode of action is related to the competition for binding sites or competitive exclusion, that is, probiotic bacteria occupy the binding sites (receptors or attachment sites) of the cells of the intestinal mucosa, thereby posing a physical barrier to pathogenic bacteria.This means that these pathogens are excluded due to competition for space (Furlan et al., 2004).Aiming at improving the efficacy of probiotics, several research studies have been carried out to develop products with different bacterial species and strains (Albino et al., 2007).
The objective of the present study was to evaluate the effects of the prebiotic Bacillus subtilis C-3102 added to diets containing or not antibiotic growth promoters at a concentration of 10 10 CFU/g on the performance of broilers at 42 days of age.

Material and Methods
The experiment was carried out at the Setor de Avicultura do Centro de Estações Experimentais do Canguiri, Universidade Federal do Paraná, Brasil.A total number of 1,200 male Cobb broilers at one day of age were used.Birds were housed in an experimental house divided in pens with the floor covered with wood-shaving litter, and equipped with tube feeders, bell drinkers, and electrical brooder.It was used a completely randomized experimental design consisting of five dietary treatments: negative control (with no growth promoters); Bacillus subtilis (30 g/t of ration); Bacillus subtilis (50 g/t of ration); Bacillus subtilis (30 g/t of ration) + colistin (10 ppm); avilamycin (10 ppm) + colistin (10 ppm).Each treatment had 10 replicates with 24 birds each.
Birds were submitted to standard management practiced in the poultry industry.Water and feed were supplied ad libitum.The experimental diets (Table 1) were formulated using practical levels applied in the Brazilian broiler industry for rations containing animal and vegetable ingredients.
The prebiotics and the antibiotics were premixed with soybean meal according to their respective treatments before being added to the mixer in order to prevent any mixing problems.Birds and rations were weighed when birds were one (placement), 21 and 42 days of age.Mortality was daily recorded, and dead birds were weighed to correct the measured parameters for mortality.Rations samples were collected to recover Bacillus subtilis and to check its proper dosage in the ration.
The following parameters were evaluated: feed intake, weight gain, and feed conversion ratio.The collected data were submitted to analysis of variance and means were compared by the test of Tukey at 5% of significance.

Results and Discussion
Analyses of Bacillus subtilis recovery were carried out to verify if the dosages were correct and if diets were cross-contaminated.The obtained values (Table 2) were as it was expected; however, the diet containing only antibiotics was cross-contaminated.
This cross contamination was probably caused by the fact that the mixture containing only antibiotics was performed after all other feeds were mixed, allowing probiotic residues to contaminate that ration.The performance results obtained for the starter phase (Table 3) did not show significant differences (P>0.05) in feed intake or weight gain among treatments; however, feed conversion ratio of the birds fed rations containing probiotics and or antibiotics was better as compared to the birds receiving the diet with no additives.Moreover, the diet containing the highest Bacillus subtilis (50 g/t of ration) level promoted the best feed conversion ratio.
The results of the present study are consistent with the findings by Flemming & Freitas (2005), Cardozo (2006), and Da Silva (2008), who also tested a probiotic composed of Bacillus subtilis, and concluded that birds submitted to the diet without promoters presented the worst feed conversion ratio.Conversely, Corrêa et al. (2003) and Lorençon et al. (2007) showed that the performance of broilers in the starter phase was not affected by the use of probiotics or antibiotics.
When the results of the finisher phase were analyzed (Table 4), birds fed diet with Bacillus subtilis (30 g/t of ration) presented feed intake lower than those fed diet containing Bacillus subtilis (30 g/ t of ration) + colistin (10 ppm).
In a similar study, Rigobelo et al. (2008) observed lower feed intake in broilers fed diets with antibiotics and prebiotics compared to those fed a diet with no additives.In terms of weight gain, the diets containing prebiotics promoted the best results relative to the negative control diet.The diets containing antibiotics and 30 g Bacillus subtilis/t/ration also promoted higher weight gain, probably due to the higher feed intake.
The results of the present experiment are in agreement with the findings by Flemming & Freitas (2005), who also evaluated the prebiotic Bacillus subtilis and obtained better broiler performance with the diets with that probiotic as compared to the diet without promoters.
Consistently with the other parameters, feed conversion ratio was better in the groups that were fed diets containing probiotics and/or antibiotics; those containing only probiotics -Bacillus subtilis (30 g/t ration) + colistin (10 ppm) and Bacillus subtilis (50 g/t ration) -promoted the best results.In this context, in the present study, it was clearly shown that the antibiotic could have been replaced by probiotics, which have the additional benefit of excluding undesirable bacteria and not stimulating bacterial resistance.
On the other hand, Silva et al. (2000), at the end of an experimental period of 42 days, verified that the use of probiotics did not influence broiler performance.Santos et al. (2004) argue that, under good health and adequate environmental conditions, the effects of probiotics may not be detected.According to Corrêa et al. (2003), as experimental conditions, where stress is minimal, are different from commercial rearing environments, it may be difficult to observe any benefits promoted by probiotics when birds are not challenged by environmental or health stressors.
In the present study, the diets containing additives (probiotics and/or antibiotics) promote better production efficiency results than the control diet (with no additives).These results are consistent with those of Lorençon et al. (2007), who observed that the use of probiotics in broiler diets resulted in similar production efficiency index as that obtained with the diets containing antibiotics.On the other hand, Da Silva (2008) did not observe any influence of the addition of the probiotic Bacillus subtilis in the feed on production efficiency.

Conclusions
The use of probiotics -with or with no antibioticspromotes higher weight gain and better feed conversion ratio and production efficiency in broilers from one to 42 days of age.The probiotic Bacillus subtilis at a dose of 50 g/t of ration improves broiler feed conversion ratio and may be used to replace antibiotic growth promoters in rations for broiler.

Table 1 -
Composition of the experimental diets

Table 3 -
Feed intake, weight gain, and feed conversion ratio of broilers at 21 days of age Means followed by different letters in the same column differ by Tukey test at 5% probability level.

Table 4 -
Feed intake, weight gain, and feed conversion ratio of broilers at 42 days of age

Table 2 -
Results of the recovery of Bacillus subtilis in the diets

Table 5 -
Production efficiency index results of broilers at 42 days of age