Dairy Note
pH
pH is an indication of acidity or alkalinity, normally measured with a pH meter. When absolute accuracy is not required, colorimetric pH papers are useful. Chemically, pH is the negative logarithm (base 10) of the hydrogen ion (H+) concentration in an aqueous solution. For example, a solution with an H+ concentration of 1 x 10-6 has a pH of 6; one with an H+ concentration of 1 x 10-5 has a pH of 5. Notice that a solution at pH 5 has 10 times the H+ concentration of a solution at pH 6.
Pure water containing no solutes has a pH of 7; an acid will have a pH < 7, the stronger the acid, the lower the pH. Conversely, the pH of a base will be > 7 with stronger (more alkaline) bases having higher pHs.
Normal pH ranges important in dairy production are as follows:
| Measured in | pH range |
|---|---|
| Cow’s urine | 7.5 – 8.0 |
| Urine of cow fed anionic minerals | < 6.0 |
| Rumen, optimum for fibre digestion | 6.0 – 6.8 |
| Rumen, optimum for starch digestion | 5.5 – 6.0 |
| Fresh cut silage crop | 6.0 – 6.5 |
| Poorly preserved silage | 5.0 – 6.0 |
| Well preserved silage | 3.8 – 5.0 |
Editor’s note, 2026: the first two rows were labelled “blood” in the original note. The ranges given are those of urine, which is what is sampled when anionic diets are monitored. Blood pH in a healthy cow stays close to 7.4.
This note comes from the original DairyWeb Dairy Notes series.