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.  

Field observations suggest that periparturient cows are at risk of subacute ruminal acidosis because of the time required for the rumen microflora and papillae to adapt to increased intakes of concentrates immediately before parturition and during early lactation when feed intake increases rapidly to meet the energy needs of high-producing dairy cows. The adaptation of the ruminal microflora and papillae from a system appropriate for forage to a system capable of utilizing high-energy lactation rations requires a gradual change over a period of 3-5 wk.

The ability of the rumen to rapidly absorb organic acids contributes greatly to the stability of ruminal pH. It is rarely difficult for peripheral tissues to utilize VFA already absorbed from the rumen; however, absorption of these VFA from the rumen can be an important bottleneck.

The ability of the rumen to rapidly absorb organic acids contributes greatly to the stability of ruminal pH. It is rarely difficult for peripheral tissues to utilize VFA already absorbed from the rumen; however, absorption of these VFA from the rumen can be an important bottleneck.

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.