North American Veterinary Licensing Examination (NAVLE) Practice Test

Acute bovine pulmonary emphysema and edema primarily occurs in cattle due to sudden changes in the diet, particularly when they are transitioned to lush, rapidly growing pasture. This change often involves a high intake of carbohydrates, particularly non-structural carbohydrates, which can lead to an overgrowth of normal gut bacteria. This overgrowth can produce excess gas and toxins, causing a rapid increase in ruminal pressure and subsequently leading to pulmonary issues.

In these lush pastures, especially those dominated by legumes, there are often high levels of protein and sugars that can contribute to this condition. The rapid diet change creates an environment in which the rumen flora adapt poorly, leading to gas production and the release of pulmonary toxins. This not only contributes to emphysema and edema but also leads to clinical signs such as difficulty breathing and diminished oxygen exchange.

While toxins from legumes, environmental stressors, and parasitic infections can affect cattle, they are not the primary drivers of acute pulmonary emphysema and edema in the context of diet changes to summer pastures. The specific impact of changing to lush pasture is a well-documented phenomenon in bovine medicine known for contributing to these acute respiratory conditions.