This article deals with the various types of acidosis and the signs that indicate subacute rumen acidosis. In addition, diagnosis and tools for diagnosis are discussed in detail.
Rumen acidosis can occur in two forms, on the one hand as subacute and on the other hand as acute rumen acidosis. The normal pH value in the rumen lays in the range between 6.2 and 7.0. According to literature, subacute rumen acidosis occurs when the pH value falls below the 5.8 range for over 300 minutes. Acute rumen acidosis occurs when the pH remains at below 5.5 for a longer period of time. Cows are not as often affected by acute rumen acidosis, however this type of acidosis is life-threatening. 
When cows suffer from SARA, it is possible that the pH value of 5.5 or less always returns to a value above 6.0. This means that SARA is a recurring acidification. Due to the recurring acidity in the forestomach system, not only is the rumen flora disturbed, but also the rumen wall and its mucous membrane are irritated and partially inflamed. 
Acute rumen acidosis leads to a refusal of feed intake and the milk yield is significantly reduced. Animals suffering from acute rumen acidosis have conspicuously light and sour-smelling diarrhea. In addition, no rumination can be observed and the animals have sour-smelling breath. Failure to treat this form of acidosis may result in the animal not moving and dying. 
Recognizing the symptoms of subacute rumen acidosis and making the right diagnosis is often very difficult as it is a very complex, herd-based disease and the symptoms are not specific. This will be discussed in more detail below.
The cause of rumen acidosis is usually an oversupply of carbohydrates, a lack of structure (structurally effective crude fiber in the ration) and as a result a decrease in buffering. In addition, the acidity in the feed may have an effect on the pH value in the rumen. SARA often occurs in early lactation when the proportion of concentrated feed in the diet is increased. In the case of feeding that is not suitable for rumination, SARA may also occur in the second or third lactation stage. The reason for this is fedd that is too high in starch. Grazing animals in particular are susceptible to this disease as they mainly eat fresh, poorly-structured grass. 
Some risk factors may favor subacute rumen acidosis:
The following symptoms can often be observed when SARA occurs:
These symptoms can be used to detect rumen acidosis. It is particularly important to examine all symptoms and to look at the relationships between them. Taking a holistic view and taking into account the feeding situation, the risks regarding a case of SARA can be assessed relatively clearly. It is of particular importance to observe the entire group or herd.
As already mentioned above, it is often difficult to diagnose subacute rumen acidosis, as it is an extremely complex, herd-based disease. For example, if a rumen pH value of less than 5.5 occurs in three out of twelve animals in a group, it can be assumed that subacute rumen acidosis is present. It is, however, not only the pH value limit that is crucial – the repeated decrease in rumen pH value indicates subacute rumen acidosis. Also, the type and timing of rumen fluid collection or measurement of the pH value has a key influence on the result. 
Three possible methods of diagnosis are:
In the case of rumen puncture, a cannula is inserted into the rumen in the flank to remove rumen fluid. The advantage of this method is that there is no saline congestion but no history of the change in pH is visible. Single removal means only current values are visible. In addition, it is indeed an operation in which a violation of the abdominal wall occurs and due to the piercing of the rumen fluid may reach the wound and lead to painful inflammation.
If a rumen gavage is used, a probe is pushed down through the mouth into the rumen and rumen fluid is extracted. Saliva-free removal of the rumen fluid is possible without injuring the abdominal wall. Again, no history is visible without renewed sampling.
With the help of smaXtec pH Plus, unfalsified data are collected, which provides direct information about feeding management and rumen health. smaXtec analyzes the pH value in the reticulum and provides the farmer with indications of an increased risk of rumen acidosis. In addition to monitoring feeding and pH values, the smaXtec technology also detects a wide range of health parameters, which additionally support the farmer in the diagnosis of disorders. Use of the bolus requires no surgical intervention and the abdominal wall, unlike with the puncture method, is not injured.
For more information on treatment and consequences, please read the next article. This takes a closer look at the smaXtec technology in connection with SARA and includes analysis of an example curve.
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