Which of the following is NOT a cause of fluid distention of a bird's coelom?

Fluid distention of a bird's coelom can arise from various underlying health conditions. The correct choice highlights an option that does not contribute to this condition. Coelomic organ enlargement typically refers to an increase in the size of the organs within the coelomic cavity, such as the liver, kidneys, or tumors. While this enlargement can cause discomfort or abnormalities in physiologic function, it does not directly lead to fluid collection or distention within the coelomic space.

In contrast, right-sided heart failure can lead to fluid accumulation due to inadequate circulation and subsequent congestion. Hypoproteinemia may result in a lack of proteins that maintain osmotic pressure, causing fluid to leak into the coelom. Reproductive diseases can likewise result in fluid accumulation due to hormone imbalances or pressure from developing eggs or tumors. Each of these options describes a mechanism that directly contributes to fluid accumulation, showing that organ enlargement itself does not serve as a direct cause of fluid distention in the coelom.