Why do some cows struggle with subacute ruminal acidosis (SARA) while others on the same ration don’t? A study published in the Journal of Dairy Science points to the cow’s biology, not just the ration, as the deciding factor.
Researchers followed 24 first-calf Holsteins from three weeks before calving to 70 days in milk. They tracked rumen pH every 10 minutes and shifted all cows from a close-up diet to a high-concentrate lactation ration. Despite eating the same feed, cows responded very differently. Based on pH patterns, they were grouped into high-, moderate-, or low-SARA.
Here’s the surprise: the overall mix of rumen microbes looked similar across all groups. However, high-SARA cows carried a few acid-tolerant bacteria, including Lactobacillus. The sharper differences appeared in how cows processed nutrients throughout the body.
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In the rumen, high-SARA cows showed stronger nitrogen and amino acid metabolism, with higher levels of nucleotide compounds.
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In the blood, they had more cholesterol esters and phosphatidylcholines, linked to steroid and bile acid production. These shifts were most evident around calving and peak lactation.
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In the milk, moderate-SARA cows—not the most severe group—produced more triglycerides and showed stronger activity in fatty-acid synthesis pathways.
Together, these results highlight that SARA is not just a ration issue. Even on identical diets, cows’ metabolic responses diverge, especially during calving and peak milk production.
For producers, the message is clear. Continue managing the basics—transition diets, effective fiber, and gradual concentrate steps. At the same time, recognize that individual cow biology matters. Blood lipids and milk fat patterns may one day serve as early warning signs for cows most at risk.
As the authors explain, “Cows consuming the same diet can have very different metabolic responses to SARA.” That underscores the need for closer monitoring of individuals, alongside careful ration management.
