Changes

==Pathogenesis==

==Pathogenesis==

The normal physiologic nadir for rumen pH is 5.5. Excessive quantities of rapidly fermentable carbohydrates in the ruminant diet results in overproduction of volatile fatty acids by the rumen microflora, lowering rumen pH below its ideal range.  

The normal physiologic nadir for rumen pH is 5.5. Excessive quantities of rapidly fermentable carbohydrates in the ruminant diet results in overproduction of volatile fatty acids by the rumen microflora, lowering rumen pH below its ideal range. Volatile fatty acids are a normal product of rumen fermentation and are readily used by tissues as an energy source. Tissues are capable of using excess volatile fatty acids (VFAs) produced from the fermentation of high levels of carbohydrate; however, the instability in rumen pH makes it difficult for these to be absorbed properly and hence put to good use.  

VFA from the rumen are absorbed passively across the rumen wall. This passive absorption is enhanced by finger-like papillae, which project away from the rumen wall. Ruminal papillae increase in length when cattle are fed higher-grain diets; this presumably increases ruminal surface area and absorptive capacity, which protects the animal from acid accumulation in the rumen. If the absorptive capacity of these cells is impaired (eg, chronic rumenitis with fibrosis), it becomes much more difficult for the animal to maintain a stable ruminal pH following a meal.

VFA from the rumen are absorbed passively across the rumen wall. This passive absorption is enhanced by finger-like papillae, which project away from the rumen wall. Ruminal papillae increase in length when cattle are fed higher-grain diets; this presumably increases ruminal surface area and absorptive capacity, which protects the animal from acid accumulation in the rumen. If the absorptive capacity of these cells is impaired (eg, chronic rumenitis with fibrosis), it becomes much more difficult for the animal to maintain a stable ruminal pH following a meal.

Intake depression is the ruminant’s last resort for regulating ruminal pH. Depressed dry-matter intake becomes especially evident if ruminal pH falls to <~5.5. Intake depression may be mediated by pH receptors and/or osmolality receptors in the rumen. Inflammation of the ruminal epithelium (rumenitis) could cause pain and contribute to intake depression during subacute ruminal acidosis.

Intake depression is the ruminant’s last resort for regulating ruminal pH. Depressed dry-matter intake becomes especially evident if ruminal pH falls to <~5.5. Intake depression may be mediated by pH receptors and/or osmolality receptors in the rumen. Inflammation of the ruminal epithelium (rumenitis) could cause pain and contribute to intake depression during subacute ruminal acidosis.