Sub-Acute Ruminal Acidosis in the Dairy Herd

Acute acidosis is a metabolic disease characterised by unexplained diarrhoea, inappetence, lethargy, bloating and, in extreme cases, death.

It is caused by a sudden drop in rumen pH usually below 5.5, often due to grain/concentrate overload. Sub-acute ruminal acidosis (SARA) is much more common in the dairy herd but the signs are often subtle and can be difficult to detect. A drop in feed intake and consequently reduced milk yield can occur, as well as milk fat depression and changes in cudding behaviour and dung consistency.

Factors increasing the risk of SARA:

  • Excessive levels of starch and sugars.

  • Low forage to concentrate ratio, with NDF from forage < 20%.

  • High levels of starchy concentrates from parlour feeding.

  • Over processed TMR with insufficient effective fibre for rumination and high inclusion of finely ground cereals.

  • Sorting of TMR (can occur if ration high dry matter, poorly mixed, inadequate processing of forages).

In the US the estimated cost of SARA per cow is $1.12 per day or £0.85 ($1 = approximately £0.76 as of 19/06/18) . For 150 milking cows with approximately 20% suffering from SARA, this costs £25.50 per day.

A practical way to identify SARA is to look at the manure and assess the three C’s; colour, consistency and content.

Colour is influenced by forage to concentrate ratio and rate of passage. When cows consume a typical TMR, dung is usually more yellow in colour. This colour results from the combination of grain and forage and varies according to the amount of grain and processing.

A normal dung pat has a porridge-like consistency and forms a dome-shaped pile 3 to 5cms high. Loose dung, with bubbles can indicate SARA as high acid production causes this change in consistency.

Undigested grain or long forage particles in dung indicates poor rumen fermentation or an accelerated rate of passage. This may be due to inadequate intake of fibre that is effective in stimulating rumination or maintaining normal rumen pH.

Presence of the above mentioned symptoms may indicate SARA and it is worth looking into diet or management changes to minimise that loss of £0.85/cow/day.


Enemark, J. M. D., 2007. The monitoring, prevention and treatment of sub-acute ruminal acidosis (SARA): A review. The Veterinary Journal, Volume 176, pp. 32-43., 01387 261172