M. Azizian - Department of Poultry Science, Faculty of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
S. Rahimi - Department of Poultry Science, Faculty of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
M. A. Kamali - Animal Science Research Institute, Karaj, Islamic Republic of Iran.
M. A. Karimi Torshizi - Department of Poultry Science, Faculty of Agriculture, Tarbiat Modares University, Tehran, Islamic Republic of Iran.
M. R. Zobdeh - Department of Animal Science, College of Agriculture, University of Tehran, Karaj, Islamic Republic of Iran.

This study was conducted to compare susceptibility of six different strains of male broilers to ascites syndrome. In this experiment, ۶۱۲ one-day-old male broiler chicks from five international hybrids (e.g, Arbor Acres, Cobb ۵۰۰, Hubbard, Lohmann, and Ross ۵۰۸) and an Iranian hybrid (Arian) were used. Growth performance, ascites mortality ratio, the ratio of right ventricle to total ventricles weight (RV:TV) in dead and healthy broilers, hematocrit values, serum levels of thyroid hormones (T۳, T۴) and T۳: T۴ ratio were studied to evaluate the susceptibility of the birds. The results showed that there were significant differences among the hybrids in ascites susceptibility. Arian and Hubbard were more susceptible, while, Lohmann was more resistant to ascites than the other hybrids. The results of this study showed that RV:TV ratio and the hematocrit value can be sensitive indicators for differentiating hybrids susceptible to ascites from the resistant ones.

Ascites syndrome, Broiler strains, mortality, Susceptibility