Acute and Subacute Ruminal Acidosis

Dr. Clell V. Bagley, D.V.M.
USU Extension Veterinarian

“Acidosis is the most important nutritional problem that feedlots face daily and is a major challenge for dairies as well.”1 Both the dairy and feedlot industries have continued to move to the use of more grains in their feeding programs. Relatively cheap grains have provided an excellent and economical energy source. But this has also resulted in an increasing problem with acidosis. It can appear in a variety of situations and with different clinical signs.

“... grains are subject to microbial fermentation in the rumino-reticulum part of the stomach complex. ... The microbial fermentation of starches contained in grains can proceed too rapidly causing the rumen to become acidotic. The severity of the acidosis may range from mild to life threatening.”1

“Acidosis is not one disease, but rather a continuum of degrees of acidosis.”1 Some of the problems that have been associated with acidosis include: Acidosis is difficult to measure in cattle and subacute acidosis is an even more insidious problem and more difficult to diagnose. It may not be possible to eliminate all acidosis and still maintain economic production, but it must at least be managed and controlled.1

Acute Acidosis:

Acute acidosis occurs with rapid grain overload and may result in the death of the animal, severe illness, liver abscesses, etc. If these problems are prolonged, the low ruminal pH may result in damage to the ruminal wall and reduced absorption capacity. Thus, even animals that survive may become chronic poor-doers.

Subacute Ruminal Acidosis (SARA):

The major sign of subacute acidosis is reduced feed intake. This makes it difficult to diagnose and separate from other problems or events that may reduce feed consumption, such as digestibility of the grain. Also, anything that interrupts normal consumption patterns can precipitate acidosis, so the usual sign of the problem can actually precipitate the problem. Other signs that may indicate subacute acidosis include: lethargy, diarrhea, panting, excessive salivation, kicking at the belly and general signs of discomfort and stress. Recognize that in feeding a pen of cattle, it is really a pen of individual cattle that are being fed. These individuals may be going through cycles of partially adjusting to subacute acidosis and thus fluctuating in their feed intake but never quite getting completely adjusted. These individual fluctuations in feed intake can make just looking at average feed intakes misleading.1

“In dairy cattle ... the bouts of low ruminal pH are probably limited to short episodes - somewhere between calving and peak intake at about three to four months post-calving. The risk for SARA is very low outside of these periods in a dairy cow’s lactation cycle.”3

Factors Contributing to Acidosis:         FAST         SLOW Diagnosis:

The current recommendations are to have your veterinarian perform rumenocentesis (sample rumen with a needle) on 12 animals per feeding group. Subacute acidosis is diagnosed if three or more have a pH of 5.5 or less. Samples should be collected at 4-8 hours after a TMR meal or 2-4 hours after the concentrate portion of a component-fed ration. Qualitative evaluation of manure can also be helpful.2

Prevention / Correction of Acidosis:

The first step is to recognize acidosis as a potential problem and all of the various factors that may relate to it. The next step is periodic monitoring to identify if it is still occurring so corrective action can be taken. If acidosis is a problem, then the likely causes (one or several) must be identified and action taken to correct them. There is a fine line between maximum performance and acidosis. The causes can be grouped into three categories: When feeding high levels of concentrates for high levels of milk production, some acidosis should be expected, but then the feeding program should also be managed so as to identify the problem early in order to minimize the effects. When the severity of acidosis is reduced, both feed intake and daily gain (or milk production) increase.1


1Stock R. Acidosis in cattle: an overview. The AABP Proceedings 23:30-37 (September 2000).

2Nordlund, K. Sore feet, sour rumens, clinical quandaries. The AABP Proceedings 23:58-64 (September 2000).

3Oetzel, G. Clinical aspects of ruminal acidosis in dairy cattle. The AABP Proceedings 23:46-53 (September 2000).