effects of atenolol on growth performance, mortality due to ascites, antioxidant status and some blood parameters in broilers under induced ascites

introduction broiler chickens are intensively selected for productive traits. the management of these highly productive animals must be optimal to allow their full genetic potential to be expressed. if this is not done, inefficient production and several metabolic diseases such as ascites become apparent. investigations in mammals indicated that the b- adrenoreceptor characteristics are differentially regulated by chronic hypoxia and play an important role in the cardiovascular system. the density of b-adrenergic receptors was higher in cardiac cells of ascites sensitive birds compared with ascites-resistant ones. moreover, the characteristics of b-adreno receptors are different in cardiac cells of birds with right ventricular hypertrophy and heart failure compared with healthy birds. treatment with the selective b1-adrenoceptor blocker, atenolol, abolished right ventricular hypertrophy in response to hypoxia compared with normoxic condition in rats. materials and methods this study investigated the comparative effects of different levels of atenolol growth performance, mortality due to ascites, antioxidant status and blood parameters in broilers under induced ascites. six hundred one-day-old male broilers (ross 308) in a completely randomized experimental design with four treatments (positive control, negative control, and two levels of 30 and 60 ppm atenolol) with five replicates of thirty birds were applied. birds in positive control were reared in natural temperature without atenolol, the other bird groups were reared in cold temperature with 0, 30 and 60 ppm atenolol. the average daily feed intake (adfi), average daily weight gain (adwg) and feed conversion ratio (fcr) for each group of birds were calculated and mortality was daily weighed, recorded and used to correct the fcr. observations were made daily to record the incidence of ascites and mortality. diagnosis of ascites generally depends on observation of the following symptoms: (1) right ventricle hypertrophy, cardiac muscle laxation; (2) swollen and stiff liver; (3) clear, yellowish, colloidal fluid in the abdominal cavity. hematological, biochemical and pathological tests were done at day 49; total red blood cell (rbc), wight blood cell (wbc), hemoglobin, hematocrit, glucose, protein, cholesterol, triglycerides, high density lipoprotein (hdl) and activity of alanine transaminase (alt), aspartate transaminase (ast), lactate dehydrogenase (ldh). also, glutathione peroxidase (gpx), superoxide dismutase (sod) total antioxidant status (tas) and malondialdehyde (mda) content of plasma were determined. at the end of experiment (wk 7), 2 chicks from each replicate were randomly selected and slaughtered. then ascetic index, rv/tv, (ratio of right ventricle weight to total ventricle weight) were calculated. results and discussion the results showed that, the atenolol-treated birds had lower right ventricle to total ventricle ratio and mortality due to ascites compared with the control birds. moreover, atenolol, significantly, reduced feed conversion ratio & average daily feed intake and reduced feed conversion ratio. it is also, atenolol, significantly lowered the lactate dehydrogenase activity in plasma. alanine transaminase and aspartate transaminase activity in plasma were not significantly affected by atenolol supplementation. other blood parameters and antioxidant incidences were not affected by atenolol. it has been proved that exposure to high altitude results in increases in plasma and urinary catecholamine, hormones that are known to increase hypertrophic actions of heart tissue and consequently changes in the function of myocardial cells such as contractile activity and cardiac output that could lead to ventricular hypertrophy. it has also been reported that the b1-adrenoceptor blocker numerically reduces the ascites incidence in broiler chickens and may have been used as a prophylactic agent. it is known that that the hypertrophic effect of catecholamine in rats such as cardiac contractility, cardiac output and, finally, right ventricular hypertrophy could be reduced by a b1-adrenoceptor blocker. this might explain, at least partially, the mechanism by which atenolol reduces cardiac output, and hence might reduce pulmonary hypertension and, finally, ascites incidence in broiler chickens. although this study shows the involvement of b-adrenergic receptors in heart failure syndrome in birds, more studies should be carried out for better understanding of the exact mechanisms that could contribute to change in cardiac function and, consequently, pulmonary hypertension in broiler chickens. conclusion this study showed that inclusion of atenolol in broiler diets had remarkable effects on performance. moreover, according to the results of this research, atenolol could reduce mortality due to ascites in broilers. we suggested that the optimal level atenolol in diet is 60 ppm.