versão impressa ISSN 1516-635Xversão On-line ISSN 1806-9061
Rev. Bras. Cienc. Avic. v.5 n.2 Campinas maio/ago. 2003
Performance and organ morphology of broilers fed microbial or antimicrobial additives and raised in batteries or floor pens1
Pedroso AAI; Menten JFMII; Racanicci AMCI; Longo FAI; Sorbara JOBIII; Gaiotto JBI
IGraduate student (PhD) in Ciência Animal e Pastagens, ESALQ/USP; FAPESP scholarship
IIPhD, ESALQ/USP; CNPq scholarship
IIIGraduate student (MSc) in Ciência Animal e Pastagens, ESALQ/USP
This study was conducted to determine the effect of microbial or antimicrobial additives on the performance and organ morphology of broilers raised in batteries or in floor pens. The effect of microbial additives on the presence of oocysts in the litter was also studied. Experiments 1 and 2 consisted of four treatments (non-supplemented control diet or diet supplemented with avilamycin, bacitracin methylene disalicylate or enramycin) and six repetitions in a randomized block design. In Experiment 1, 288 day-old chicks were housed in heated batteries in a environmentally controlled room, 12 chicks per cage; in Experiment 2, 1,200 day-old chicks were housed in a curtain-sided experimental house, with concrete floor and rice hulls as litter material, 50 chicks per pen. Experiments 3 and 4 were carried out similarly to Experiments 1 and 2, respectively, but the treatments consisted of microbial additives (non-supplemented control diet or Bacillus subtilis added to the feed plus Lactobacillus reuteri and Lactobacillus johnsonii added to the water, undefined microflora added to the water or live yeast added to the feed). The antibiotics did not affect the performance of birds raised in batteries, but improved feed conversion, weight gain and live weight when chickens were kept on the floor pens. Microbial additives did not affect bird performance in any environment; however, treatments affected liver weight. Microbial agents increased intestinal weight in floor-raised broilers. No relationship was seen between the use of microbial additives and the presence of oocysts in the litter.
Keywords: antibiotic, broilers, growth promoters, organ morphology, performance, probiotic.
The use of antibiotics in subtherapeutic doses as additives in animal diets is used since the 1950's. Antibiotics represent a group of compounds with heterogeneous chemical structures and different physico-chemical properties, with a common property of antibacterial activity (Jong et al., 1985a). Antimicrobials would have the ability to select intestinal microflora, suppressing unfavorable bacteria and stimulating the growth of beneficial bacteria, resulting in better animal performance. There are, however, criticisms related to the possibility of development of bacterial resistance to antimicrobials, which would lead to a lower therapeutic efficiency of molecules. Besides, there are emerging requirements of antibiotic residue-free products by importers (Henrique, 1998). In July 1999, the European Union decided to discontinue the use of four widely used antibiotics, tylosin, virginiamycin, spiramycin and bacitracin zinc (Jin et al., 2000). In such context, microingredients from microbial origin, such as bacterial probiotics, live yeasts and undefined lyophylized microflora from the intestinal tract of healthy birds, have received special attention as an alternative to the use of traditional growth promoters.
Microbial additives are based on the simbiosis principle, in which there is association of superior organisms with bacterial flora resulting in reciprocal benefits for both. Beneficial unicellular organisms might decrease the surviving rates of pathogenic bacteria, improving normal flora stability and utilization of ingested nutrients (Fatec, 1997). The products have been, thus, commercialized with the promise of colonizing the intestinal tract of the bird and protecting it against pathogens (Day, 1996) and even against coccidiosis. It was observed that a mixture of Lactobacillus fed to broilers stimulated the immune function of the birds and was able to decrease Eimeria acervulina infection rate after challenge (Lundeen, 2001).
Some experiments developed with antimicrobial and microbial agents evaluated the relative weight (as a percentage of live weight) and the weight of small intestine per linear centimeter, which are good indicators of changes in the morphology of the small intestine. Growth promoters are indicated as modifying agents of the intestinal wall thickness due to the elimination of prejudicial bacteria (Coates et al., 1955; Eisser & Somer, 1966; Rosen, 1995), so that germ-free birds may have lighter intestinal tracts than the birds originated from commercial farms (Coates et al., 1981). Jong et al. (1985b) studied the action of antibiotics in the organism of broilers and reported physical alterations in the structure of the intestine. The decrease in the intestinal mass may result in less utilization of nutrients by the mucosa, which resulted in nutrient economy by the birds (Henry et al., 1987); nevertheless, when the characteristic was evaluated in birds submitted to diets with antimicrobials (Loddi et al., 2000) and with microbial additives (Pedroso, 1999) no significant differences were found.
Broilers reared on floor pens covered with litter may show a different performance from birds reared in batteries due to the challenge degree they are exposed to. In field conditions, maybe no disinfecting system for poultry houses and equipments can guarantee that germ-free birds are raised, which prevents the bird from fully expressing its genetic potential. Cromwell et al. (1991) stressed that the beneficial effect of growth promoters is greater in field conditions, with responses up to two times greater than the responses observed in experimental facilities, due to differences in hygiene practices, stress and pathogen presence.
The objective of this study was to evaluate the performance and the morphometry of organs in broilers supplemented with microbial or antimicrobial agents and raised in metal batteries or in floor pens with rice hulls as litter material, and also to evaluate the effect of microbial agents on the frequency of oocysts in the litter.
MATERIAL AND METHODS
Four experiments were carried out according to a randomized block design with four treatments and six repetitions for all experiments. Male AG Ross broiler chicks with mean body weight of 45 g were used.
Treatments in Experiment 1 and 2, using antimicrobials were: Control diet without growth promoter, Avilamycin diet containing 10 mg/kg avilamycin, Bacitracin diet with 27.5 mg/kg bacitracin methylene disalicylate, and Enramycin diet with 12.5 mg/kg enramycin. Experiments 3 and 4 were carried out with microbial additives, using the following treatments: Control diet without growth promoter additive, Lactobacillus + B. subtillis 0.05 mg/L of product containing Lactobacillus reuteri and Lactobacillus johnsonii (Finelact®) given in the drinking water on the first day for four hours and 300 mg/kg of product containing Bacillus subtillis (Calsporin®) added to the diet throughout the experiment; Microflora 0.0625 mg/L of product containing lyophilized bird flora (Aviguard®) added to the water at the first day of age during four hours, and Yeast 400 mg/kg of product of live yeast added to the diet throughout the experiment (Biosaf®).
Experiments 1 and 3 were conducted in batteries, in an environmentally controlled room during 21 days. Initially, 288 birds were housed, 12 birds per experimental unity. Experiments 2 and 4 were carried out in a poultry house with concrete floor covered with rice hulls during 42 days. Initially, 1,200 birds were used in parcels of 50 birds housed in pens of 4.5 m2. For analysis of the intestine (weight and length), gizzard (weight), heart (weight) and liver (weight), two birds were killed per parcel at 21 days in Experiments 1 and 3, and at 21 and 42 days in Experiments 2 and 4, after feed withdrawal for 6 hours. The birds and feed were weighed weekly, and data of weight gain, feed intake, feed conversion and livability were obtained.
By the end of Experiment 4, in which microbial products were given to birds raised on rice hulls, litter samples were collected from all pens. An imaginary line was drawn from the door to the wall and the material was collected from five different points (50 centimeters from the drinker, under the drinker, between the drinker and the feeder, under the feeder, and 50 centimeters from the feeder). The material was homogenized and an aliquot of 500 grams was taken to the laboratory for oocyst count.
Isoproteic corn-soybean diets were produced (Table 1) according to the recommended levels of National Research Council - NRC (1994). The treatments with microbial or antimicrobial supplementation were obtained by adding the products to the ration. No anticoccidial additive was added to the diets.
Performance and organ morphology data were analyzed by the General Linear Models of SAS (1998) and the means were compared by Tukey's test. Oocyst frequency (presence or absence) was analyzed by the Generalized Linear Models of SAS (1998).
RESULTS AND DISCUSSION
There was no effect of antibiotics on the performance characteristics in the experiment carried out in batteries (Table 2). Nevertheless, when the same treatments were evaluated in the poultry house, there was significant effect of the antibiotics on weight gain and feed conversion from 1 to 21 and from 1 to 42 days (Table 3). Birds fed enramycin showed better weight gain than the birds fed avilamycin in the period from 1 to 21 days and showed better feed conversion when compared to the bacitracin and control groups. From 1 to 42 days, the groups receiving enramycin and avilamycin had higher weight gain than the control birds. Feed conversion was better in the groups fed enramycin and avilamycin than the groups fed bacitracin and the control group. Broilers supplemented with antimicrobial and kept in batteries did not respond to the treatments, whereas better performance was seen for the birds raised in floor pens and fed antimicrobials. Maybe the intestinal microflora of the birds on the floor pens have influenced the results with the use of the products, since the birds raised in batteries did not show any change in the performance. In a review on the antimicrobial effect in broilers, Butolo (1999) concluded that weight gain and feed efficiency were 3.5% and 3.4% better, respectively, when compared to the control group. In the present study, there was better weight gain of 3.0% in the group fed enramycin and 2.9% in the group fed avilamycin, while the improvement in feed efficiency was 2.4% and 2.5%, respectively, values very close to those reported by Butolo (1999). As for the organ morphology data, there were no significant differences for birds raised either in batteries (Table 4) or in the poultry house with rice hull litter (Table 5).
In the experiments carried out with microbial products in batteries (Table 6) and on the floor with rice hull litter (Table 7), no beneficial or prejudicial effect was observed on the performance characteristics. Groups fed diets without microbial additives had performance indexes similar to the treated groups. Possibly, the environment in which the birds were reared, batteries or floor, was not able to influence the performance of the birds that were not fed with supplements. In an experiment carried out with microbial additives, Maiorka et al. (2001) observed that broilers from the control group had lower performance than the birds receiving the microbial products. It is interesting to note that organ morphology characteristics showed changes in liver weight in the birds fed rations supplemented with yeast, with higher values (p<0.02) when compared to other treatments (Table 8). Conflicting results were seen for the birds raised in the poultry house at 42 days (Table 9), in which birds fed yeast showed reduction of the liver if compared to the group without microbial products. The treatments Lactobacillus + B. subtillis and Microflora were shown to be able to promote an increase in intestinal weight (g/cm) in birds reared on floor with rice hull litter, when compared to the control group.
In all experiments, it was observed a slight increase in the coefficient of variation of the performance data in batteries if compared to the data from birds reared on the floor. These increased values can be attributed to the maximum capacity of housing in each experimental unity, 12 birds per battery cage versus 50 birds in each pen of the poultry house. The coefficients of variation observed for the organ morphology characteristics can, also, be due to the number of sampled birds in the experiments.
No association was observed between the presence and absence of oocysts in the litter and the supplementation with microbial additives (Table 10); treatments had no effect on the frequency of oocysts at the level of 55%. Even without the utilization of anticoccidial additives, no evidence of the pathogen presence was observed in the rice hulls litter or in the birds, and when the parasite was observed in the laboratory analysis, oocyst count was low, from 133 to 800 oocysts/gram of litter. Possibly, the experimental facilities offered the birds low challenging conditions. However, if in conditions of controlled challenge situation, such as the oral inoculation of Eimeria oocysts, the products would have had some effect on the control of the protozoarium.
Antimicrobial additives may be satisfactorily used as growth promoters for the birds reared on the floor, and there was no evidence of a favorable effect of the microbial additives on the performance and the incidence of oocysts in the litter.
There is no evidence of a favourable effect of the microbial additives on the performance and incidence of oocysts on the litter.
To Claudia Cristina Paro de Paz for helping with statistical analysis and to FAPESP for financial support.
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José Fernando Machado Menten
Departamento de Zootecnia ESALQ/USP
Av. Pádua Dias, 11
13418-900, Piracicaba SP Brazil
Arrived: april 2002
Approved: april 2003
1 - Part of the PhD thesis of the first author, grant from FAPESP (nº 00/07853-9).