It’s long been speculated that heat stress caused by increasing ambient temperatures could reduce the ruminal pH and therefore amplify the risk of subacute ruminal acidosis (SARA). Proposed mechanisms for this include reduced feed intake during heat stress and therefore reduced rumination and saliva production to buffer the rumen.
An article published in the Journal of Dairy Science in 2008. even showed some very compelling evidence for an association between heat stress and decreased ruminal pH.
Comparing the average (mean) daily ruminal pH of cows (measured by the eBolus) with the ambient temperature (information from wunderground.com), no such correlation was found. Below is the combined records from two dairy cows on a farm in Somerset presented with the ambient air temperature for the specific days. While it could be argued that the 4th, 5th and 6th show some negative correlation, the rest of the data shows anything but.
Visual analysis of these two graphs clearly shows that the relationship between ruminal pH and temperature is not as simple as high temperatures decreasing the ruminal pH. Further analysis is needed before any clear cut conclusions can be draw between these two factors.
Each data point for rumen pH is an averaged value from multiple cows, each cows average utilising 96 recorded readings our bolus takes over a 24 hour period. And each reading the bolus records (every 15 mins) is an average of 15 readings taken at minute intervals.