High-density, pelletted ration, superior management and environment cause rapid growth in the birds. This can result in an increased body demand for oxygen. Alternatively, this increased demand can be caused by cold, activity, hyperthyroidism, overeating, or a diet including ingredients requiring increased oxygen for metabolism. The increased demand for oxygen in the bird's body may cause increased cardiac output. This may be expressed as hypoxemia, either from hypoxia (high altitude, severe rickets), reduced O2 carrying capacity (carbon monoxide, anemia), or lung pathology affecting membrane diffusing capacity. It may also be expressed as hypervolemia (sodium + toxicity). The increased cardiac output leads to increased pulmonary arterial pressure. This pressure may include insufficient vascular capacity in the pulmonary capillary bed (primary pulmonary hypertension), organic vascular obstruction (poly-
cythemia, megalocytosis, reduced red blood cell deformability, emboli, lung pathology narrowing capillary bed), hypertension (sodium + toxicity), cardiac defects (left to right shunts) or valvular lesions, and hypoxic vasoconstriction. The increased arterial pressure causes right ventricular dilation/ hypertrophy, which in turn can cause either increased intravascular pulmonary pressure, resulting in hypertensive lung edema and sudden death; or valvular insufficiency and right ventricular failure. The latter causes liver congestion & edema which results in ascites.





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