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The language of nutrition: SARA (Sub-acute ruminal acidosis)

Tony Hall Published on 24 August 2015


In layman’s terms, what does sub-acute ruminal acidosis (SARA) mean?



The period when the cow’s rumen pH is below 5.8 for more than three hours at a time is known as sub-acute ruminal acidosis (SARA).

Higher pH levels in the rumen are important because when pH is below 5.8, the animal’s ability to use the ration efficiently is impaired and can lead to other, more serious health problems.

The modern lactating dairy cow can take between six to 10 meals in a 24-hour period. This naturally leads to fluctuating pH throughout the day. It’s been documented that lactating cows can spend up to 11.8 hours with a rumen pH below 5.8, which can mean nearly half a day of impaired digestion.

When pH is depressed, volatile fatty acids (VFAs) accumulate in the rumen fluid. After a meal, VFA production can exceed the capacity of the rumen to absorb the VFAs. When this occurs, the rumen pH drops, and it can lead to a bout of SARA. This cascade of events can be further complicated by other challenges, such as heat stress.



How do you knowif a cow has SARA?

The most practical way to evaluate SARA risk is through ration analysis, management and identification of herd health. Commonly, cattle will eat more sporadically or reduce their feed consumption.

Other signs of SARA include decreased efficiency of milk production, reduced fat test, a higher incidence of milk component inversions, poor body condition score, unexplained diarrhea and episodes of laminitis. Rumen pH can also be measured and monitored by means of a pH bolus or rumenocentesis.


What impact doesit have on a ration?

SARA persists despite the adoption of TMRs and in-feed dietary buffers. Producers should take note when feeding high-forage rations, which will not necessarily avoid SARA either. In fact, the majority of forage in TMRs today is corn silage, which contains about 0.4 pounds of kernel-processed high-moisture shell corn per pound – making SARA a real danger even with higher-forage rations.


Access to long-stem forage and other sources of physically effective fiber are important to minimize the effects of slug feeding and sorting of the diet.

When SARA occurs, however, rumen function isn’t optimized to make the best use of any ration. Probiotic feed additives can help improve rumen function and increase fiber digestion. Certain strains of Saccharomyces cerevisiae have been shown to help maximize rumen function in all life stages of dairy cattle.

Research shows cows fed an active dry yeast probiotic specifically selected to maximize rumen function spend significantly more time above the SARA threshold and even produce 2.1 pounds more per day of 3.5 percent fat-corrected milk per cow per day.


What percentage of dairiesare affected by SARA?

SARA can occur surprisingly often and silently affects production. It can lower herd performance by an estimated $1.12 per cow daily and is estimated to affect 10 to 40 percent of dairy cattle – making it the most important nutritional issue of dairy cattle on a herd basis. It’s an issue all dairies can be on the lookout for and then benefit from additional milk yield and better productivity.


What other nutritionconcepts would you want producers to learn about as much or more than this one?

Helping dairy cattle maintain a more consistent rumen pH can optimize rumen function – avoiding SARA and making the best use of a carefully formulated ration which, in turn, leads to greater productivity.

Other factors, like heat stress, can further impair rumen function as well. Work with your nutritionist to establish feeding and management programs to address SARA and help your cows perform at their optimal level – even during heat stress. PD

References omitted due to space but are available upon request. Click here to email an editor.

Tony Hall
  • Tony Hall

  • Dairy Technical Service Manager
  • Lallemand Animal Nutrition, North America