What’s Wrong With My Herd? Part 8 - Sub-acute ruminal acidosis (SARA)


SARA will affect feed efficiency, therefore increasing feeding costs due mainly to the decrease of fiber digestibility.
When pH drops below 6.0, the populations and growth of cellulolytic bacteria and ruminal fungi decline, impairing fiber digestibility. According to several sources, every 0.1 decrease in pH reduces fiber digestibility by 3.6%. Poor fiber digestibility and lower feed efficiency resulting from SARA translate into increased feeding costs for producers.
One study showed that short bouts of SARA (less than 30 minutes) did not reduce neutral detergent fiber (NDF) digestibility, while repeated bouts of four hours did. These findings support the use of total mixed ration (TMR) and free, 24-hour access to the feed bunker as key management tools to control SARA.

Main causes of SARA

  • Poor adaptation of rumen microflora to diet changes. Common at calving, paired with other metabolic diseases such as ketosis and related conditions.
  • Improper feeding patterns and cows selectively choosing their feed.
  • Inappropriate forage particle size.
  • Formulation mistakes.

Feed intake effects

SARA commonly causes erratic eating patterns and reduces feed intake. When the pH drops, the cow reduces its feed intake, decreasing the production of acids and driving the pH back to normal levels. The cow will then resume eating, resulting in another bout of SARA and repeating the cycle. This variation will not only decrease production due to the lower feed intake, but will also reduce the efficiency of the rumen fermentations due to the variation of the nutrient supply, causing further economic losses.

Feces assessment and SARA detection

TIP: SARA can cause a heterogeneity of feces in a group of cows in the same lactation stage. In this situation, some feces will be normal and some too loose. You can use the 1 to 5 scoring system to assess them. Figures 1 and 2 are shown as examples.

Figure 1. Feces with a score of 3 (out of 5) | Figure 2. Feces with a score of 1 (out of 5)

Figure 1. Feces with a score of 3 (out of 5) | Figure 2. Feces with a score of 1 (out of 5)
Figure 1. Feces with a score of 3 (out of 5) | Figure 2. Feces with a score of 1 (out of 5)


Lameness is a major concern in modern dairy and beef production due to implications for welfare and profitability.
There is a clear link between acidosis and the inflammation of the lamellar tissue of the hoof, a condition known as laminitis. Laminitis not only causes problems in itself, but is also a predisposing factor for other conditions such as sole ulcers and white line hemorrhages.
Although this mechanism for lamnitis is not yet completely clear, it is thought that the condition is due to lower systemic pH during acidosis, and substances such as histamine (involved in the immune response) and endotoxins entering the bloodstream.
Lameness, in turn, can exacerbate SARA as cows suffering from this condition will change their feeding patterns to lower the number of meals consumed due to the pain suffered when moving to the feeding bunker.


  • Check feeding patterns of the TMR. If cows are selectively choosing their feed, evidenced by lots of holes in the TMR (Figures 3 and 4), then the ingested fiber and concentrates can differ considerably from the theoretical ration.
  • Routinely assess and document indicators of possible SARA such as butterfat content (reduced during SARA), manure assessment (too loose in affected individuals) and individual feed intake patterns.


Figure 3 and 4. Examples of cows selecting their feed creating holes in the TMR.
Figure 3 and 4. Examples of cows selecting their feed creating holes in the TMR.

SARA control aims at improving adaptation of rumen papillae and microflora and optimizing effective fiber intake. Here is a list of management practices to mitigate the risk of SARA:

  • Ensure proper rumen adaptation especially at calving when shifting cows from the dry group to the lactation group.
  • Control the palatability of ingredients.
  • Ensure homogeneity of the TMR and proper forage cut length. Keep records of mixer maintenance (balances, knives).
  • Ensure proper access to feed bunks and an adequate supply of water.
  • Avoid stressful situations such as moving animals too much between production groups.

Keep first-calving heifers separated from older cows when possible. • Ensure good layout, maintenance and bedding in resting areas. Insufficient lying time will cause cows to change their feeding pattern. • When formulas or forages are changed, a smooth transition is highly advisable.

SARA can have a serious impact on milk production, general health and longevity.

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