Cardio-pulmonary hemodynamic and immunological responses to endotoxin in broilers under various environmental conditions

Intravenous endotoxin triggers a delayed pulmonary hypertensive response that varies widely in magnitude and duration among individual broilers. It was proposed that this individual variability may reflect immunological differences acquired during previous respiratory challenges that might have subsequently altered the endotoxin-initiated biochemical cascade, or genetic variability that may be associated with susceptibility to pulmonary hypertension syndrome (ascites). To test the hypothesis that previous respiratory challenge or preexistence of intrapulmonary inflammation may change pulmonary responsiveness to endotoxin, we compared the pulmonary hypertensive responses to i.v. endotoxin in broilers that had different levels of preexistent respiratory challenges. In one experiment, broilers in which the pulmonary vasculature had been immunologically challenged 48 h previously by an i.v. injection of cellulose micro-particles (Primed) were compared to the controls (Unprimed). The microparticles were trapped in the pulmonary vasculature and initiated acute focal inflammatory responses within the surrounding lung parenchyma. Granuloma/lymphocyte aggregates developed around the trapped particles within 3 h and progressed in size throughout the 48 h post-injection period. In a subsequent experiment, broilers reared in clean stainless steel cages and broilers reared on floor litter which presents a higher respiratory challenge were compared. The results showed that preexistence of intrapulmonary inflammation or a higher environmental respiratory challenge did not affect the pulmonary hypertensive responses to subsequent i.v. Salmonella typhimurium endotoxin challenge in terms of time of onset, magnitude, or duration of the responses, as well as the variability of among individual birds. Accordingly it is suggested that variation in the hypertensive responses to endotoxin among individual birds might be inherited. The current studies demonstrated that housing conditions affect the general well-being of broilers. When compared with broilers reared in clean stainless steel cages, broilers reared on floor litter exhibited impaired pulmonary gas exchange function and had increased arterial partial pressure of CO₂ . Broilers reared on floor litter also had lower heterophil and monocyte concentrations, and a lower heterophil to lymphocyte ratio in the blood. The immune system of the floor-reared broilers appeared desensitized and exhibited less pronounced blood leukocyte responses to i.v. endotoxin. However, such desensitization did not help broilers survive i.v. endotoxin challenge.