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Arquivo Brasileiro de Medicina Veterinária e Zootecnia

Print version ISSN 0102-0935On-line version ISSN 1678-4162

Arq. Bras. Med. Vet. Zootec. vol.52 n.3 Belo Horizonte June 2000 

Effect of clenbuterol on growth performance in broilers

[Efeito da adição de clenbuterol na dieta sobre o crescimento de frangos de corte]


R. Ortiz M., A. Valdivia F. J. Martínez R., A. Martínez de A.

Centro Ciencias Agropecuarias, Universidad Autónoma de Aguascalientes
Apartado Postal No. 3, Jesús María, Aguascalientes
C.P. 20900, México


Recebido para publicação, após modificações, em 9 de dezembro de 1999.




The objective of this study was to evaluate the effect of clenbuterol (CB), a b2-adrenergic agonist, as a growth and weight gain promoter in broilers. Effects of CB were assessed, mixing it in feed at 0.0, 0.21, 0.42 and 0.84ppm, and feeding during four weeks to four groups (n=75) of 28 day-old Arbor Acres chickens. The body weight (BW) and food intake at 0, 12, 20 and 28 days of the study were recorded. Also abdominal fat (AF) and total muscle proteins were measured. Results indicate that from day 20 until the last of the experimental period (56-day-old), efficacy of CB was evident to increase growth and decrease AF deposition rates (P<0.01), in a dose-response pattern, suggesting that CB has a profitable growth promoting effect in broiler chickens.

Keywords: Chick, clembuterol, muscle protein, weight gain, abdominal fat, food conversion



Avaliou-se o efeito da administração de clenbuterol (CB) como promotor de ganho de peso em frangos, dos 28 (início do experimento) aos 56 dias de idade (final do experimento). CB foi adicionado às dietas nas dosagens de 0 (controle), 0,21, 0,42 e 0,84ppm. Utilizaram-se 75 frangos em cada tratamento, registrando-se o peso corporal, o consumo de alimento, a gordura abdominal e a proteína muscular. A partir do 20º dia do experimento (48 dias de idade) até o seu final o efeito da administração de CB foi significativo. Frangos que receberam dosagens mais elevadas de CB estavam mais pesados. Observou-se também diminuição na deposição de gordura no abdômen com o aumento das dosagens de CB na dieta.

Palavras-chave: Frango de corte, clenbuterol, ganho de peso, gordura abdominal, conversão alimentar




The advances on food agricultural commodities for human population have been based on several methods, from genetic progress to the addition of pharmaceuticals in animal diets such as anabolic steroids. However, most of the alternatives have carried a considerable fat deposition in carcass, producing a negative effect on marketing and production cost. On the other hand the excessive human consumption of saturated fats is a risk factor to cardiovascular diseases (Fain & García-Sáinz, 1986; Buttery & Dowson, 1989), reducing the demand for this kind of meat. These facts have provoked a shift of attention to adrenalin- and noradrenalin-analog compounds, which have shown evidences of having an important effect on increasing the production of lean meat and reducing the amount of fat deposition (Cardoso & Stock, 1996). Such compounds are known as b -adrenergic agonists (BAA) because of their interaction with b-adrenergic receptors (BAR) in some organs (Ahlquist, 1948). Clenbuterol (CB) is a BAA which, with other compounds like salbutamol, have been used as a traditional bronchodilator or tocolytic (Nuytten et al., 1986). Some results (Bohorov et al., 1987) gave evidence of CB effects on muscular development and lamb total muscle protein (MP) concentration, due to BAR stimulation, mediated mainly by the b2-receptors located in skeletal muscle. BAR have also neurotransmission and hormone properties, related to stimulation of cardiac function; blood vessels, intestines and bronchi tones, as well as some metabolic pathways. Rosi et al. (1993) fed New Zealand rabbits with diets containing CB in 0.5 and 1.0 mg/kg and found a 9% weight increase and a 11% hepatic weight decrease at slaugther but without changes in food intake (FI), therefore concluding that CB induces an adaptation mechanism, which reduces hepatic mass and nitrogen requirements to mantain homeostasis. In addition, CB shows effects on fat deposition. In this regard, Coleman et al. (1985) showed that BAA reduced the amount of fat cells in lambs. The usefulness of CB as growth inducer has not been assessed, during the finishing growth period in broiler chickens; in this period there is a maximal gain in muscle mass. Therefore it was thought of interest to develop a controled trial to evaluate the effects of CB added to a broiler chicken diet on body weight (BW) and abdominal fat deposition (AF).



For this experiment, 300 male Arbor Acres four-week-old (28 days) were obtained from a local hatchery and randomly alloted to four floor pens (75 birds per pen) and maintained at the broiler house of Centro de Ciencias Agropecuarias, Universidad Autonoma of Aguascalientes (UAA). Distribution and treatments are shown in Table 1. Chopped straw was used as litter and stocking density was held at 0.067m2 per bird. These experimental chickens were separately placed in the poultry house facility. Lighting schedule provided 23h of light per 24h throughout the entire experiment.



CB (Ventipulmin, Ingelheim Boehringer Laboratory) was added to four broiler finisher diets in 0.0, 0.21, 0.42 and 0.84ppm each. The finisher diet was made in UAA Feed Factory according to Nutrient... (1984) and supplemented with vitamins and minerals, but not with antibiotics. The CB supplemented-diets were supplied to assigned pens during 28 days. Control birds received the unsupplemented diet, without the drug.

At 0, 12, 20 and 28 days from the initiation of the experiment, individual live BW and feed intake (FI) per pen were recorded. At the eighth wk of age the birds were slaugthered according to Ley Estatal de Proteccion a los Animales Ley... (1996), and AF was weighed. Samples of breast meat were homogenized with a pH 7.4 buffer solution, using a Potter Homogenizer and stored at –70ºC until total proteins were assayed. Additionally a food conversion index was measured.

Breast meat proteins were measured according to Peterson (1977). Analysis of variance was performed using General Linear Model procedure (SAS, 1989-96). Significant difference of CB within treatment means were contrasted by Duncan’s multiple range test (a = 0.05).



Until 28th day of treatment (56-day-old) mean BW values of broilers (Table 1) treated with increasing doses of CB, showed that from the beginning until the 12th day of treatment, there were no significant differences among groups. However from the 20th day of treatment to the end of the trial, a positive effect was evident, mainly in the group that received 0.84ppm (Fig. 1). FI and feed conversion index were not different among groups during the experiment (Fig. 2 and 3). However, the group that consumed the highest dose of CB, showed a tendency of requiring less food per kg of BW (Fig 3). In the relationship between AF and BW, the former decreased markedly in a dose-dependent pattern (Fig. 4). Significant differences in breast meat protein were not found between groups.










In the present study, significant beneficial effects of CB were observed on weight gain and abdominal fat reduction. Both effects are highly relevant, since they would result in reducing costs to achieve an animal with a higher amount of lean muscle mass and at the same time with a lower amount of fat tissue. A similar effect has been reported earlier by Dalrymple et al. (1984) and Dalrymple & Ingle (1988), describing a significant increase in broiler BW fed with CB from 28 to 48 day-old. In other experiments summarized by Scholtyssek (1988), using similar compounds conducted in the United States and West Germany, a consistent increase in weight gain was observed although effects on body fat were not addressed in this study. Muir et al. (1985) found that weight gain was increased in broilers fed with a diet added with L340,333, one BAA developed to livestock.

Results suggest a beneficial effect attributable to CB intake, noticeable in the increase of BW and decrease of AF. Buyse et al. (1991) did not find a significant benefit in total weight gain, although did in some particular muscles such as digitorum longus, as well as an increase of 14.9% in MP. Discrepancy may be due to the kind of compounds, doses, bird strain and trial span, because those studies have been conducted in different conditions. In other studies Reichel et al. (1993) reported positive effects on weight gain reaching 24%, and decrease of fat up to 30% on rats. Macri et al. (1993) found that in spite of lack of adequate nutritional requeriments, broilers treated with BAA increased BW, MP and decreased corporal fat. Similarly Zhou & Han (1994) established that giving different doses of CB to ducks along 25 days, breast meat weight increased up to 31%, AF decreased up to 37%, RNA:DNA ratio in breast meat was increased and a decrease of acid uric concentration in blood was also found.

In this study, weight average of the group that consumed 0.42 ppm decreased from the 20th day of treatment, probably due to the fact that this dose increased metabolic pathways such as glycogenolysis and glyconeogenesis. However with the highest dose, this probable effect was compensated by growth induced by BAA compound.

According to known effects of BBA that show a striking reduction on fat deposition after long time supplementation in all species, results of this experiment are outstanding, with a clear effect in abdominal fat. Young et al. (1995) reported that CB and analog compounds decreased fat deposition and increased protein synthesis in lambs, cows, pigs and broilers, when administered orally or parenterally. However the major effect has been observed in females. Maybe because they have a higher tendency to accumulate fat than males. This agree with results published by Dalrymple & Ingle (1988), that reported a better effect on AF than on breast fat.

Unlike other meat type animals, the primary site of lipogenesis in poultry is the liver according to Leveille et al. (1968). Later Neal et al. (1987) reported that in vivo studies with avian hepatocites, BAA provide an important mechanism for regulating lipogenesis.

In this study, the amount of AF was lower in the highest dosage. Such facts are in agreement with Merkley & Cartwrigth (1989), who suggested a reduction of adipocyte size more than a decrease in number of cells. Cardoso & Stock (1996) published that under ad libitum feed conditions, there are not changes in FI, but there is in fat amount in CB-treated animals. The results have support on those findings.

In summary, results showed that CB given 28 to 56-day-old broilers had a beneficial effect on weight gain, and the duration of the treatment at the finishing period is improving the effect of the dosis of CB. The best dosis was 0.84 ppm, suggesting that it was the most effective to promote growth and reduce fat deposition in broilers, under the period of growth studied.



We thank to Universidad Autónoma de Aguascalientes for the support to PIP/PT 97-3 project, to Victor Franco and Laura Yamamoto for his cooperation and her technical support. We also thank to the staff of Unidad de Producción e Investigación Avícola, Centro de Ciencias Agropecuarias.



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