The Effects Of Heat Stress On The Development Of Experimental Colibacillosis In Broiler Chickens

Colibacillosis is a common infectious disease that makes chicks dead and decreases production performance in broiler chickens. It has been found that E. coli infection and heat stress decrease femoral artery pressure of broiler chickens. This paper is to find out whether the E. coli infection combined with heat stress may ulteriorly decrease the femoral artery pressure of broiler chickens, and affect the development of colibacillosis in broiler chickens. Two hundred-forty broiler chickens were divided into normal temperature group (21℃), heat stress group (37℃), normal temperature-infection group, and heat stress infection-group. Broiler chickens of infection groups were all inoculated with 0.5 ml nutrient broth suspension with E.coli (O₂ standard strains, 2.1×10⁹CFU/ml) by an intraperitoneal injection to induce colibacillosis. The clinical signs, the mortality, the pathologic changes, and the hemodynamics of broiler chickens in different groups were continuously examined on the 1 st, 2nd, 3rd and 7th day after the treatment.1. Heat stress blocked the development of colibacillosis in broiler chickens: The clinical signs and pathological changes (cardiopericarditis, perihepatitis and air sac inflammation) of the broiler chickens with E. coli infection and heat stress were less severe than those of the broiler chickens with only E. coli infection. The mortality of the heat stress infection group (10%) was significantly lower than that of the normal temperature infection group (55%), (P < 0.01). The results showd that heat stress blocked the development of colibacillosis in broiler chickens in a way.2. Heat stress ulteriorly decreased the production performance of broiler chickens with E. coli infection: The feed intake of broiler chickens with E. coli infection and heat stress decreased obviously (P < 0.01) compared to that of the broiler chickens with only E. coli infection, and its body weight was lower than that of the broiler chickens with only E. coli infection.3. Heat stress ulteriorly decreased the hemodynamics of broiler chickens with ï¿¡. coli infection: (1) The femoral artery pressure (FAP) and the maximum increasing rate of femoral artery systolic/diastolic pressure (FA±dp/dt max) of birds with E. coli infection were sigenificantly lower (P < 0.01) , but the pulmonary artery pressure (PAP) and right ventricular diastolic pressure (RVDP)were sigenificantly higher (P < 0.05 ) than that of birds in normal group. The results indicate there are low hemodynamics with FAP fall and pulmonary hypertension in the development of colibacillosis in birds. (2) FAP and PAP of birds in heat stress group were all sigenificantly lower than those of birds in normal group (P < 0.01) , which were different to the E. coli infection group. (3) FAP, FA±dp/dt max, PAP, the right ventricular systolic pressure and the ±dp/dt of right ventricular pressure of birds in the heat stress-infection group decreased significantly compared with those of birds in norml temperature-infection group (P<0.05, P<0.01) . The data indicate that Heat stress ulteriorly decreased the hemodynamics of broiler chickens with E. coli infectionThe conclusion: Heat stress ulteriorly decreased the hemodynamics of broiler chickens with E. coli infection, but significantly decreased mortality of colibacillosis in broiler chickens. These showed that heat stress blocks the development of colibacillosis in broiler chickens.