Use of zinc bacitracin as a performance enhancer in broilers

In order to achieve hihg protoxtion rates and for their product to be competitive, broiler producers can use several commercial products. Performance-enhancing antimicrobials (PEA), are ingredients classified as husbandry additives, and their use in broilerfeeds tend to result in improved animal efficiency and performance. Nevertheless, the use of such products has been question mainly in the European Union, where powerful consumers pressure exists in the search of antimicrobial-free foods. In Brazil, the use of these products is allowed in the regulations issued by the Ministry of Agriculture, Livestock and Food Supply (MAPA). These regulations hbird been in force since 2004, when in addition, the definition of maximum inclusion levels of each antimicrobial changes, making pharmaceutical companies to observe the new rules. Despite of the upper limits established, the actual inclusion rate is up th the formulator so that, depending on the antimicrobial, such levels can vary considerably. Zinc bacitracin, for example, has maximum recommended limit of 55 ppm. Nevertheless, while observing such limit, the formulator can include doses above the ones actually needed to enhance animal performance thus making the ration more expensive. This is why the knowledge of the best inclusion level can be essential for an efficient, least cost formulation. Ths objective of this study was to evaluate the effect of using various zinc bacitracin levels, within the MAPA-recommended limits, on 1-21 broiler performance.

One thousand five hundred (1,500) one-day-old Cobb-500^® male chicks from a commercial hatchery were used. Birds were distributed among 60 pens. Each pen was equipped with a heating system based on a 200 V incandescent lamp, one hanging drinker and one cylindrical feeder. Reused litter obtained in a commercial broiler housed was used, aiming to create environmental contamination, so that the experiment would mimic field conditions. Even though, this was not proven by microbiological litter analysis. A completely-at-random design was used with 5 treatments and 10 repetitions each. The experimental feeds were formulated based on corn and soybean meal, as isonutrient diets in accordance with Cobb Management Manual.

Feeds included two phases i.e., pre-starter (1-7 days) and starter (8-21 days). The antimicrobial was 15% zinc bacitracin. The experimental treatments included 5 inclusion levels (0, 10, 25, 40 and 55 ppm), assigned to each experimental group, while feed and water were given ad libitum throughout the experiment. Drinkers were washed only twice per week aiming to increased challenge levels. At the end of each phase, the birds and the remaining feed were weighed as to calculate feed intake (FI) weight gain (WG) and feed conversion rate (FCR).

Results were subjected to analysis of variance, and the F test was applied using the Analysis of Variance System (Sistema de Análisis de Varianza, SISVAR) for balanced data, described by Ferreira (2000). Whenever significant, the effects of treatments were subjected to regression analysis for a more detailed study of the antimicrobial levels.

In the 1-to-21-day-period, a significant effect of dietary zinc bacitracin was seen on all variables studied (P<0.05) (Table 1).

Table 1. Feed intake (FI), weight gain (WG) and feed conversion rate (FCR) in the broilers fed various levels of zinc bacitracin during the phase from 1 to 21 days

For the FI variable, a linear response was seen (P<0.05) (FI = - 0.000458x + 1.299562; R² = 50.42%), and a lower FI was seen (1,264 g/bird) when 55 ppm zinc bacitracin were used. The higher FI was sewen with the diet containing 0 ppm bacitracin, for an estimated increease of 2.4%. Therefore, in agreement with the equation, birds fed the zinc bacitracin-added feed showed a lower FI in the period from 1 to 21 days. Likewise our results, Sims et al. (2004) found decreased FI in turkeys when fhe feed contained 55 ppm bacitracin.

When the effects of bacitracin levels on WG were analysed, a quadratic response was seen (P<0.05) (WG = - 0.000027x² + 0.001568x + 0.897036; R² = 52.84%). The level of inclusion of 29.3 ppm was considered to maximize WG (920 g), which means an increase of nearly 3% over the birds that did not receive bacitracin in the feed (0 ppm). Data showed that despite that the equation estimated  a higher FI in the birds not receiving the antimicrobial, this increased FI was not enough to increase WG. Our results are consistent with those reported by Engberg et al. (2000), and Brennan et al. (2003) who found a higher WG in the birds justified by the difference in the microbiological profile in the small intestine. A positive effect was seen of the use of zinc bacitracin in the feed over FCR (P<0.05) (FCR = - 0.000675x + 1.434360; R² = 69.73%), with a linear response in the levels, with improved FCR (1.40) when 55 ppm bacitracin were used in the feed. The highest FCR (1.44) was seen in the non-bacitracin-fed birds (P<0.05), which represents a difference of nearly 3% between both treatments. Despite of the difference in FI in the birds not receiving sinc bacitracin, the difference was not enough as to be reflected on WG, which resulted in increased FCR. For the bacitracin treatments, decreased FI did not halt WG, resultinf in reduced FCR. Therefore, FCR was improved as a result of a better ability of the birds to utilize dietary nutrients.

The results from this study show that zinc bacitracin is an efficient performance enhancer in broilers from 1 to 21 days, with an optimum FCR when 55 ppm zinc bacitracin are used in the feed.

Brennan J, Skinner J, Barnum DA, Wilson J. 2003. The Efficacy of Bacitracin Methylene Disalicylate when Fed in Combination with Narasin in the Management of Necrotic Enteritis in Broiler Chickens. Poultry Science 82:360-363.

Engberg RM, Hedemann MS, Leser TD, Jensen BB. 2000. Effect of Zinc Bacitracin and Salinomycin on Intestinal Microflora and Performance of Broilers. Poultry Science 79:1311-1319.

Ferreira DF. 2000. Sistema de análise de variância para dados balanceados - SISVAR. Lavras: UFLA.

Sims MD, Dawson KA, Newman KE, Spring P, Hooge DM. 2004. Effects of Dietary Mannan Oligosaccharide, Bacitracin Methylene Disalicylate, or Both on the Live Performance and Intestinal Microbiology of Turkeys. Poultry Science 83:1148-1154.