Three hundred and fifteen day -old chickens were used to test the relationship between oxygen-derived free radicals and the biochemical, hematological and pathological alterations(associtd with ascites). They were randomly divided into three experimental groups and ascites were developed in two groups of animals by exposing them to low temperature or administration of triiodothyronine (T3,), and the third group was used as control. Different hematological, biochemical and pathological tests were used to determine the incidence of ascites in birds. These include total red blood cell (RBC), hematochrit (PCV), activities of alanine transaminase (ALT) and aspartate transaminase (AST) and the ratio of right ventricular weight to total ventricular weight (RV/TV). Two hydroxylated salicylic acid (SA) metabolites, 2, 3- and 2, 5-dihydroxy benzoic acids (2, 3- and 2, 5-DHBA), were measured by HPLC system to detect the generation of hydroxyl (OH.) radicals. An analysis of variance (ANOVA) was used to determine the differences between different experimental groups. Ascites syndrome was observed in T3 and low temperature treated groups as shown by necropsy changes and significant increases (p<0.05) in the amount of RBC, PCV, ALT, AST and the ratio of RV/TV. While the significant increase was shown in the amounts of 2,3- and 2,5-DHBA from day 11, the alteration in the values of enzymes and hematoloic parameters and ratio of RV/TV occurred from days 18, 25 and 32 respectively. It can be concluded that OH._ radicals may be involved in the initiation of ascites syndrome, but the biochemical, hematological and pathological changes induced by these agents, can cause ascites and other alterations.
Key words: ascites, free radicals, triiodothyronine, salicylic acid, broiler chickens.