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CONTRIBUTOR(S): Owen Atkinson, Sophie Mahendran,

Subacute ruminal acidosis

Subacute ruminal acidosis

SARA is a condition that is unfortunately all too common in dairy cows. It is one of the most important rumen health problems in the UK.


Rumen fluid collection (rumenocentesis) used for SARA diagnosis
©Alice Johnson

What are the causes and signs of SARA?

SARA can be induced experimentally by either feeding insufficient fibre, resulting in insufficient cudding, or feeding excess starch (cereals) – particularly if overprocessed and/or heat treated which makes it very quickly fermentable in the rumen. Of the two methods, research suggests it is the latter which seems to cause the greatest ill-health effects.

Signs include:

  • Reduced or cyclic feed intake.
  • Decreased milk production.
  • Reduced milk fat (this is a poor indicator).
  • Poor body condition score, despite adequate feed intake.
  • Unexplained diarrhea.
  • High rates of culling or unexplained deaths.
  • Sporadic cases of caudal vena cava syndrome.

SARA has a negative impact on profitability both through reduced productivity and increased veterinary bills.

What are the predisposing factors?

Generally female dairy cows are affected. Cows are at greatest risk of SARA, during early lactation.

Risks factors for SARA and poor rumen health include:

  • High concentrate feeding.
  • ‘Slug feeding’: large concentrate feeds, for example in the parlour. This can also occur when TMR diets are subject to sorting, and/or the feed intake is not spread evenly through the day in many feeding bouts. Lame cows, for example, tend to have fewer but larger meals, which are effectively slug feeds.
  • Not enough fiber in the diet, or physically effective fiber which stimulates cudding.
  • Insufficient forage intakes (physically effective fiber) – such as when there is competition at troughs/insufficient feedspace/poor palatability of forage.
  • Diet sorting leading to insufficient fiber intakes for some cows.
  • Poor transition cow management (poor rumen acclimatization).
  • Heat stress (less time spent cudding).
  • Poor cow comfort: lower lying times (less cudding).
  • The normal (healthy) rumen operates at between pH 5.6 and 6.5: below pH 5.5, the healthy rumen bugs can’t survive, and unhealthy rumen bugs are favored (which produce stronger acids, and lower the pH even more).

What are the effects on fertility?

There are 3 principle ways that SARA reduces fertility:

  • Poor populations of rumen bugs. This means the rumen is not working efficiently and can’t digest the fibre which is an important energy source. The cow goes into more severe negative energy balance.
  • Cows stop eating; sometimes for a short period while the rumen recovers, and again have insufficient energy.
  • Cows have greater amounts of starch which by-pass the rumen. Whilst the cow can cope with small amounts of starch by-passing the rumen and being digested in the small intestine, large amounts undergo secondary fermentation, causing over-growth of unfavorable bacteria in the hind gut and production of toxins.

Low energy reduces fertility (and causes weight loss and thin cows). The toxins produced have direct effects on ovaries, reducing egg quality and hormone production.

How is it diagnosed?

SARA is a herd condition and is often under-diagnosed.

If >25% of the animals tested have a ruminal pH <5.5, then the group is considered to be at high risk of subacute ruminal acidosis.

SARA can be difficult to diagnose and can only be done in one of two ways, your veterinarian will determine the most appropriate method:

Assessing rumen fluid samples

Collected either by rumenocentesis (by needle), or stomach tube. A minimum of 12 cows should be tested. pH is determined on a pH meter.

Data colected from special (telemetric) rumen pH boluses

These are inserted in a representative sample of the herd.

How is SARA treated?

SARA is a result of less than optimal dietary management and therefore, the focus should be on improving feeding and management practices. Secondary conditions, such as foot/lameness issues arising from poor body condition may require specific treatment.

Modify cow nutrition such that the rumen is given time to adapt to high-grain diets.

A veterinarian and or nutritionist MUST be contacted before any alterations are made to the diet.

Aim to have a good working relationship with your veterinarian and nutritionist, so that all can work together to optimize cow heath and productivity.

What can be done in the long-term?

Monitor the status of your herd. Look at all farm records, in particular milk yield (hopefully starting to increase) and medicines use (hopefully starting to decrease), and monitor rumen pH.

Ongoing assessment of diet, by veterinarian and/or nutritionist, to ensure it is optimal for your herd.

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