Preventing Sub-Acute Ruminal Acidosis (SARA) in dairy cows

Sub-Acute Ruminal Acidosis (SARA) is a metabolic disease of cattle that is commonly seen in freshly calved dairy cows at grass in springtime. It has a significant negative effect on incomes on dairy farms due to loss of milk yield, lower quality milk constituents, poorer BCS, infertility, etc. It is present in 10 to 15% of grazing cows and in 20 to 40% of cows in confined high production systems.


What is it and what causes it?

SARA is a metabolic disease that occurs when the pH in the rumen goes below 5.5 pH. The digestive system is at its most efficient at a pH of between 5.8 and 6.3 and the maximum benefit from the diet is achieved. Below 5.5 pH, the digestive system is less efficient, with fibre digestion decreasing by up to 25% due to the bacteria responsible for fibre breakdown being intolerant to changes in pH. Rumen bacteria, in general, are less efficient at lower pH levels as is nutrient absorption across the rumen wall.

Diets containing high levels of rapidly fermentable carbohydrates (starches and sugars) will reduce rumen pH. Diets with low fibre content, particularly, structural fibre will also contribute to SARA. Cows fed on diets that consist of fresh spring grass and concentrates with high levels of cereal/maize are prone to SARA. Feeding programmes, such as feeding high levels of concentrates twice a day, can influence SARA susceptibility, as ruminal pH fluctuates during the day, being at its lowest during night hours. Diet formulations that are nutritionally unbalanced will contribute to SARA.


There is no one indicator that confirms SARA is present in the herd. It is a combination of factors that will determine if SARA is present. Reduced feed intake, poor milk composition, reduced milk yield, scouring, etc. may be indicators of SARA, but they may not be all present at the same time. A very soft, watery dung pat with bubbles present is a strong indication of reduced ruminal pH, particularly if there is some undigested fibre present. If milk fat is less than milk protein by 0.4% for 10% of the herd or if milk fat is less than 2.5% for 10% of the herd, then SARA could be suspected. Lack of rumination (chewing the cud) is another indication of SARA – 80% of the herd should be lying down chewing the cud 2 to 3 hours after being turned out into the paddock.



Low ruminal function and poor utilization of the diet are probably the most significant consequences of SARA. Everything else leads on from these issues. Low rumen pH greatly inhibits fibre digestion which has a negative influence on milk fat percentage which, in turn, has financial implications. Because the diet is not digested efficiently, a lot of nutrients and energy are not available to the cow. This means that BCS, overall milk composition, milk yield and fertility will suffer. Cows use up their body/fat reserves to produce milk (‘’milking off their back’’) and thin cows are difficult to get back in calf!

The immune system is also compromised, which means the cow is more susceptible to diseases and illnesses such as mastitis and grass tetany. SARA may also have an effect on lameness but this is not certain.



SARA is difficult to prevent as it can occur at various times during the cow’s lactation, especially in early lactation. High quality grazed grass and concentrates containing high levels of cereals, particularly, wheat, will predispose dairy cows to low rumen pH and SARA. Therefore, it is essential to provide a fibre source or rumen buffers to the cow at vulnerable times. Diets should have at least 21% NDF (neutral detergent fibre) coming from forage to buffer against pH drops in the rumen. There should not be more than 35% starch & sugar in the diet for the same reason. Straw (chop length = 7cm), good quality high dry matter baled silage, maize silage, etc., are excellent sources of fibre/buffer feeds for dairy herds grazing lush spring grass. Concentrates should also have a good source of fibre included, such as, soya hulls and beet pulp. Other ingredients, such as, palm kernel meal and sunflower meal, may also be included in spring/summer concentrates, as a fibre source only. Rumen buffers (Yeassac, AcidBuf, ActiSaf, etc.) are included in most concentrates, now, as standard. They are all effective against rumen pH drop.

If you have any queries about any issues raised in this article, please contact your Cooney Furlong representative, or call into your nearest Cooney Furlong branch.