Consecutive reticular pH monitoring in dairy cows fed diets supplemented with active dry yeast during the transition and mid-lactation periods

•Changes in reticular pH during the close-up period in dairy cows were monitored.•SARA cows in the period had typical pH profiles compared to non-SARA cows.•The effects of yeast supplementation on reducing the risk of SARA were also evaluated.•Yeast supplementation did not prevent the postpartum decrease in reticular pH.

To determine changes in reticular pH during the pre- and postpartum periods, when subacute ruminal acidosis (SARA) frequently occurs, we monitored pH in dairy cows up to 12 weeks postpartum using a radio transmission pH sensing system. We designated seven pregnant multiparous Holstein cows for continuous pH monitoring (pH monitoring test), resulting in successful data acquisition for reticular pH. We subsequently evaluated the cows to determine whether active dry yeast supplementation of their feed was effective for SARA prevention (yeast supplementation test). Twenty- nine pregnant cows were allocated to two groups (control [CON, n = 15] and yeast- supplemented [YEA, n = 14]) and fed a mixed ration optimized for dry prepartum cows and a mixed ration that consisted mainly of timothy hay and a commercial concentrate. The feed of the YEA group was supplemented with 10 g/day of commercial active yeast product for three weeks prepartum and twelve weeks postpartum. In the latter test, six cows in each group were selected for reticular pH recording using the pH monitoring system. The pH profiles in the pH monitoring test were relatively high compared to those in the yeast supplementation test throughout the testing period, probably due to differences in starch and fiber levels between experiments despite their identical formula design. Notably, regardless of yeast supplementation, 11 of 12 cows in the latter test exhibited similar trends of pH maintenance (6.5 < pH < 6.8) or gradual decrease during the dry period, whereas average daily reticular pH decreased dramatically after calving. Supplementing the diet of dairy cows with yeast during the transition period provided no significant change in the health and performance measurements of the animals. We demonstrated the application of a radio transmission pH sensing system for assessment and monitoring of the ruminal pH of cows in the transition period. Furthermore, our results imply that SARA incidence in the transition and early- to mid-lactation periods may be attributable to a reticuloruminal pH decrease during the dry period, which is difficult to overcome by means of yeast supplementation during the transition period.