Effect of Chronic Heat Stress on Performance and Oxidative Damage in Different Strains of Chickens

Heat stress (HS) causes poor growth, immunosupression and high mortality, through physiological dysfunction. We have reported that 'acute' HS increases mitochondrial reactive oxygen species (ROS) and oxidative damage in the skeletal muscle of broiler chickens (Cobb), but that this is not for the case for males of the laying-type white leghorn (WLH) strain of chickens (Mujahid etal., 2005b). We have now studied the effects of 'chronic' HS on performance and oxidative damage to skeletal muscle in different strains of chickens. Meat-type male chickens (Ross and Cobb) and male laying-type chickens (WLH) of 14 d of age were arranged according to a factorial design (3 strains X 4 conditions): control (24 C), cyclic (32-24 -32 degrees C: 32 degrees C for 8 h/d, 32-24-32 HS), constant (32 and 34 degrees C, 32 HS and 34 HS, respectively) for 14 d. Feed consumption and body weight gain were measured. Thiobarbituric acid reactive substances (TBARS) content in skeletal muscle was measured colorimetrically with BHT (butylated hydroxytoluene) and expressed as malondialdehyde (MDA) equivalent. Body weight gain and feed consumption for the 3 strains (Ross, Cobb and WLH) were decreased by 32 HS and 34 HS, but not by 32-24 -32 HS. The decrease in weight gain of WLH chickens for the 32 HS and 34 HS conditions was smaller than for broiler chickens (Ross and Cobb). The 32 HS and 34 HS groups showed slightly enhanced MDA levels (P<0.05) in the skeletal muscle of all 3 strains, but not for the 32-24-32 HS group. The results suggest that depression in growth performance due to chronic heat stress is more evident in meat-type chickens (Ross and Cobb) than male laying-type chickens (WLH), and that reduction in the performance are associated with enhancement of oxidative damage to skeletal muscle.