The use of additives as an alternative to antimicrobials on broiler performance

Introduction

The trend to avoid using antimicrobial growth promoters in the feed has resulted in a more intensive search of alternative feed additives that have the ability of maintaining animal productivity while not affecting the quality of the end product. Among such alternatives, probiotics, prebiotics, symbiotics, organic acids, etc. Fuller (1989) defined a probiotic as a feed supplement constituted by live organisms that, once in the body, exert beneficial effects by improving the intestinal microbiota balance. Prebiotics have been defined as feed additives that are not digested in the proximal gastrointestinal tract, that benefit the host by selectively promoting the growth and/or activity of a number of bacteria in the intestine (Gibson and Roberfroid, 1995), while the term symbiotic is used for products containing both pre and probiotics in an association.

The most studied prebiotics are oligosaccharides, mainly mannan oligosaccharides (MOS), that consist of cell wall fragments of Saccharomyces cerevisae, and have the ability of binding the fimbria of pathogenic bacteria, in such a way that they are excreted with the feces, away from the body (Spring et al., 2000). As an outcome the digestive tract is colonized by beneficial organisms that prevent the establishment of pathogens including Salmonella, Clostridium, Escherichia coli, etc. (Oyofo et al., 1989).

The organic acids are commonly found in nature as normal components of animal and plant tissues. It has been clearly established that organic acids have powerful antimicrobial properties and, therefore, they are broadly used in the animal nutrition industry to control de growth of bacteria and molds.

These positive effects of organic acids can be explained through various mechanisms including a pH lowering effect, bacteriostatic properties, and various metabolic properties of the anionic portion of these acids after dissociation (Bellbirdr and Scheuermann, 2004).

Several studies have shown that these additives promote the beneficial modulation of the intestinal microbiota, a trophic effect on the intestinal mucosa, and immunomodulating effects. The outcome is improved digestion and absorption of nutrients, thus imrpoved animal performance wit no risk for the consumer and without major increases in production costs (Santos et al., 2005).

The puirpose of this study was to evaluate the effect of performance-enhancing feed additives as an alternative to antimicrobials (one probiotic, one prebiotic, one symbiotic, and organic acids) on broiler performance (weight gain, WG; feed intake, FI; feed conversion rate, FCR; and productive efficiency index PEI).

Materials and Methods

The experiment was performed in the facilities of the College of of Veterinary Medicine, UNESP, Botucatu campus, SP, Brazil. One thousand and eighty (1,080) one-day-old, male, Cobb broilers were used at a stocking density of 12 birds per m². The experimental design was completely at random, with 6 treatments (T) and 6 30-bird repetitions. The feeding regime included 4 phases i.e., 1 (1-10 days), 2 (11-21 days), 3 (22-35 days) and 4 (36-42 days). T1 (control): basal diet with no antimicrobials or additives; T2: basal diet plus the antimicrobial enramycin (Enradin® F80, 10 ppm for phase 1, and 5 ppm for all other phases); T3: basal diet + probiotic (a commercial product including anaerobic bacteria, 10⁷colony-forming units [CFU]/g, lactose-fermenting enterobacteria, 10⁵ CFU/g, Enterococcus spp. 10⁶ CFU/g, and Lactobacillus acidophilus 10⁷ CFU/g at the dose rate of 150 g/ton for phase 1, and 100 g/ton for all other phases); T4: basal diet + prebiotic (mannan oligosaccharides, 1 Kg/ton for phase 1, and 500 g/ton for all other phases); T5: basal diet + symbiotic (T3 + T4); T6: basal diet + organic acids (commercial product including the following microencapsulated acids: fumaric (64.1%), calcium propionate (10.3%), calcium formiate (20.5%) and potassium sorbate (5.1%) at the dose rate of 600 g/ton for all phases).

The basal diet was formulated with corn and soybean meal, following the recommendations issued by Rostagno et al. (2005) and given ad libitum throughout the experimental period. The chicks were coccidiosis-vaccinated in the drinking water on day 2 of age, and no anticoccidial drugs were provided in the feed throughout the experimental period. In order to enhance the challenge, re-used litter was used. In order to evaluate performance results (WG, FI, FCR, livability and PEI), the amounts of feed consumed were recorded, and the animals were weighed at the beginning and at the end of each phase. Mortality was recorded daily to determine actual FI.

FI was estimated by the difference between the weight of the feed offered and the feed leftovers at the end of each phase, divided by the number of birds in each treatment. WG was estimated by the difference between the start weight and the end weight in each phase, divided by the number of birds in each treatment. FCR was estimated using FI and WG in each phase, and the result was corrected to consider the weight of birds that died during the period. Livability was obtained by the difference in the number of birds at the beginning and at the end of each phase. The results are shown as percentages. the PEI was calculated using the formula: (daily weight gain (g) x livability(%)) / (feed conversion rate x 10). Results were subjected to analysis of variance using the SAS (Statistical Analysis System, 2004) software. The differences among the means were subjected to Tukey´s test, using the GLM (General Linear Models) procedure, at a level of significance of 5%. FI parameters at 21 and 35 days of age needed to be subjected to Duncan´s test, since Tukey´s test showed no differences among the means.

Results and Discussion

In the prestarting period (1-10 days), and in the interval from 1 to 21 days of age, the controls showed the lowest (P<0.05) WG value as compared to both the antimicrobial and the symbiotic in the prestarting period, while no statistical differences were found between the alternative additives and the antimicrobial (Table 1).

Table 1. Mean weight gain (WG), feed intake (FI), feed conversion rate (FCR), livability (LIV) and productive efficiency index (PEI) in the broilers, in the following grow out intervals: 1 - 10d; 1 - 21d; 1 - 35d; and 1 - 42 d of age, with the various feed additives

Variables	Treatments
Control	Antimicrob¹	Probiotic	Prebiotic	Symbiotic	Org Ac²	CV³ (%)
1-10 days
WG (g)	209.85 b	236.75 a	232.08 ab	225.50 ab	239.78 a	226.19 ab	5.67
FI (g)	284.17	296.94	288.71	292.39	288.33	281.11	3.56
FCR (g/g)	1.37 b	1.25 a	1.24 a	1.29 ab	1.20 a	1.24 a	4.02
LIV (%)	98.89	100	98.89	100	100	100	0.99
1-21 days
WG (g)	874.14 b	940.00 a	881.07 ab	900.08 ab	894.41 ab	891.99 ab	3.88
FI (g) *	1277.93 c	1324.75 ab	1284.26 bc	1336.38 a	1290.18 bc	1299.02 abc	2.59
FCR (g/g)	1.47	1.41	1.47	1.49	1.45	1.46	3.09
LIV (%)	97.22	99.45	98.33	98.89	99.45	99.45	1.96
1-35 days
WG (g)	2234.26	2265.43	2228.34	2218.89	2218.52	2186.74	2.62
FI (g) *	3600.71 ab	3676.18 a	3602.47 ab	3676.68 a	3590.88 b	3669.58 ab	1.70
FCR (g/g)	1.63 a	1.64 a	1.64a	1.67 ab	1.65ab	1.69 b	1.72
LIV (%)	95.56	97.22	95.00	97.78	95.00	98.33	4.09
1-42 days
WG (g)	2848.79	2907.30	2825.04	2851.98	2849.25	2790.67	2.88
FI (g)	4955.27	5025.86	4947.55	5073.11	4941.55	5040.27	2.41
FCR (g/g)	1.77 ab	1.75 a	1.80 ab	1.80 ab	1.77 ab	1.83 b	2.01
LIV (%)	92.78	95.00	90.55	95.00	92.78	97.22	5.36
PEI	356.32	376.31	338.30	357.57	354.52	354.11	7.48

^{Means followed by different letters in the same line are statistically different by Tukey´s test (P<0.05) except for * (FI at 21 and 35 days of age), which differ by Duncan´s test (P<0.05). 1Antimicrobial (enramycin); 2Organic acid; 3Coefficient of variation.}

These results differ from those of Paz et al. (2010) who found no differences in the WG of birds treated with either a probiotic or a probiotic in the 1 - 10 day period. For the 1 - 35d and 1 - 42 d of age, no significant effect was seen of the treatments on WG. Likewise, Santos et al. (2005) found no differences in the total grow out from 1 to 42 days of age. Nevertheless, Kabir et al. (2004) found increased WG in the probiotic-treated birds as compared to the controls in all grow out phases studied (2nd, 4th, 5th and 6th weeks of age).

FI in the 1 - 21 and the 1 - 35 day of age intervals was influenced by the treatments (P<0.05). In the 1 - 21 day period, the alternative additives showed a similar FI to that of the antimicrobial-treated group, but no differences were seen with regard to the controls, with the exception to the prebiotic that resulted in a higher FI as compared to the controls. Iji et al. (2001) found that the use of oligosaccharides can cause increased FI. In the 1-35 day interval, the highest FIs were seen in the antimicrobial and the probiotic treatments, as compared to the symbiotic, but none of the treatments differed from the controls.

As far as FCR is concerned in the 1-10-day prestarter phase, the alternative feed additives not only showed a result similar to that with the antimicrobial, but a significant differences existed (P<0.05) with the controls, with the exception of the prebiotic. Paz et al. (2010) reported similar results. The treatments had no significant effect on FCR for the 1-21-day period. In the period from 1 to 35 days of age, the treatments with the antimicrobial, probiotic, prebiotic, and symbiotic caused similar FCRs but with no difference with the controls, while the organic acid resulted in the worst FCR (P<0.05) as compared to the controls. For the total grow out period from 1 to 42 days, the alternative additives had similar a FCR to that of the antimicrobial, with the exception of the organic acid, but none of the treatments differed from the controls. Maiorka et al. (2001) disagree from these results, since they reported improved FCRs with a probiotic, a prebiotic, and a symbiotic when compared with the controls, in the period from 1 to 45 days of age.

The performance parameters livability and productive efficiency were not influenced (P>0.05) by the treatments.

Conclusion

The performance-improving feed additives studied herein can be used in broiler feeding to replace antimicrobials, without compromising broiler performance.

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