Assessment of Two Boluses for Measuring pH in the Forestomachs of Cows

Forestomach acidosis can impair nutrient utilisation and uptake in dairy cows. Agroscope tested the functioning of two makes of measurement boluses that record pH in the forestomach of cows.

High-starch rations can cause acidosis in the forestomachs of dairy cows. Even very young, sugar-rich grass can trigger a reaction of this type. Various surveys have shown that subacute forms of forestomach acidosis (SARA, or subacute rumen acidosis) without clear clinical symptoms are common. SARA is often not recognised even by specialised staff, since the symptoms are not specific enough. In addition to other effects, SARA can impair the functionality of microorganisms in the rumen, interfere with nutrient utilisation, and reduce nutrient absorption in the digestive tract. Furthermore, SARA can trigger other diseases. Continuous measurements with pH boluses inserted by mouth into the forestomachs make it easier to detect SARA sooner in at-risk animals, so that the necessary countermeasures can be initiated. A prerequisite for this is that these pH boluses measure forestomach pH for as long and as accurately as possible.
The aim of the 2016 study was to test the smooth functioning and measuring accuracy of two makes of pH boluses over a lifetime of 150 days.

Differences in the lifetime of both products

During the trial, the average lifetime of the six eCow boluses inserted two-at-a-time in each of three cows was 82 days, with two of the boluses only functioning for 28 days. Furthermore, measurement-data readout from the eCow boluses was arduous and time-consuming. By contrast, all of the Smaxtec boluses recorded pH for exactly 150 days. A permanently installed base station close to the milking parlour ensured trouble-free readout of the measurement data from the Smaxtec boluses. In this connection, we should mention that a new version of the eCow bolus also uses a base station for the readout – how well this now functions has not yet been tested.

The Smaxtec boluses measure too-low pH

The measuring accuracy of the boluses was in each case tested under standardised conditions for a short time outside of the cows, in solutions with a pH of 4 and 7. Although there were no systematic errors in the pH values measured with the eCow boluses, there was a wide spread of deviations. By contrast, the Smaxtec boluses measured a systematically lower pH value compared to the reference. Per time of measurement and bolus, the spread of the deviation of the Smaxtec measurements was half that of the eCow bolus.

The pH measurement error differs between the Smaxtec boluses

Since almost 50% of the readings for the eCow boluses were missing, a detailed examination of the factors influencing the measurement error was omitted. It was possible to carry out this examination for the Smaxtec boluses, however. The pH of the solution to be measured – pH 4 and pH 7 – as well as the timing of the measurement influenced the error. The measurement error differed according to the Smaxtec bolus used, which casts doubt on the reliability of an individual pH measurement.


  • The functioning of the eCow pH boluses in this trial was unreliable. Moreover, reading out the measured values was arduous and time-consuming, which was not the case with the Smaxtec boluses.
  • Although the Smaxtec boluses functioned very reliably, a too-low pH was systematically measured. In addition, the error range was frequently larger than stated by the manufacturer.
  • The measurement error of the Smaxtec boluses was influenced by the pH value of the solution, the time of the measurement, and the bolus used.
  • Both types of pH boluses have since undergone further development. Measurements to determine whether they now function more reliably are pending.
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