1Department of Animal Science, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran
2Animal Science Research Institute, Karaj, Iran
The objective of this study was to assess the importance of strain and sex and their interaction effect on broiler chickens’ performance and susceptibility to ascites. Chicks from three strains (Ross 308, Cobb 500 and Arian, labeled as A, B and C respectively) were obtained from the same age breeder and sexed when one-day-old. Each crosses’ sex was assigned to four pens of 60 broilers each. Body weight gain (BWG), feed intake, feed conversion ratio (FCR) and ascites mortality were determined. At the age of 28 and 49 d haematocrit values, arterial pressure index (API = right ventricular/total ventricular weight ratio), the values of plasma thyroid hormone concentration (thyroxin, T4 and triiodothyronine, T3) and metabolic lung weight (lung weight/body weight(0.75)) were determined. Strain B had the highest BWG but an equal incidence of ascites as strain A, which had low BWG and ascites mortality. Ascites mortality was not correlated with BWG and FCR. A significant strain interaction by sex on feed conversion (P<0.01) and final weight (P<0.05) was found. The sex effect was significant only in strain C on feed conversion and final weight. Strains B and C had lower thyroid hormones and reduced metabolic lung weights compared with strain A. The sex effect was not significant on the parameters associated with ascites syndrome and its incidence.