How Important is Rumen pH?

Rumen pH is critical for cow health and milk production. Feeding a balanced ration throughout the twenty-four-hour period will keep rumen pH constant.

Fibre is one of the main sources for good rumen health, but it is a very complex carbohydrate, and its digestion is totally reliant on source. The amount and rate of digestion of the fibre determines its energy value. The most easily fermented fibres are ‘Pectins’ which are found in sugar beet and citrus pulp. Pectins are an excellent source of Rumen energy that are fast fermenting, but they do not affect Rumen pH.

The ease of digestion of fibre is dependent on:
• Fibre degrading bacteria prefer a pH of 6.7 but these will die if pH drops below 6.2
• The lignin content of feed. The maturity of that fibre will also have an impact on rumen bacteria to break the lignin down
• The particle size for the activation of rumination, encouraging cudding which also produces natural saliva which in turn keeps rumen pH constant.

After feeding at 9.00 and 13.30 rumen pH has dropped from 6.8 to below 5.5. Acidity increases reaching a dangerously low-level impairing fibre digestion. It rises at 16.00, continuing to rise throughout the night. Possible causes are feeding too much concentrate at one time, typical example – milking time. High fizzy starch will cause acidity in the rumen, upsetting the pH and rumination, which will lead on to Acidosis especially in ‘freshly calved cows’ – Subacute Ruminal Acidosis (SARA).

The above photo shows Rumen pH Cycle similar to the graph shown earlier, acute acidosis occurs with a pH lower than 5.5.

Preventing Acidosis
It all starts at harvest time, catching the crop at the right stage for cutting, grass harvesting – allowing for at least a 24-hour wilt will concentrate sugar levels needed for good fermentation which will reduce the acid loading in the clamp.

It is important to challenge your forages, whether grazing or feeding a Total Mixer Ration (TMR), feeding good quality forages that are sampled regularly will give you or your nutritionist the base tools to balance the ration.

For an independent assessment of your cow rationing, contact Mark Yearsley at or your local FCG Office.

Posted in Business Management, Dairy & Forage, Sherborne.