The temperature and pH of the contents of the reticulorumen of cattle can be monitored using sensors placed in a rumen bolus. In this research communication we test the hypothesis that these measurements can be used as a predictor of the likelihood of reproductive success. The study was performed on 20 Lithuanian Black and White dairy cows. The pH and temperature of the contents of their reticulorumens were measured using boluses manufactured for animal care (smaXtec animal care technology®). The data from reticulorumen were recording at 1 to 7 and 7 to 56 d post calving and then post insemination (on average 60 ± 12) until 170 d after calving. The pregnancies were tested with ‘Easy scan’ ultrasound 30–35 d after insemination. Those cows which were pregnant were assigned to the PD+ group (n = 12), and those which were not pregnant – assigned to the PD− group (n = 8). Rumen pH was initially lower in the PD+ group but then higher than in PD−, but temperature did not differ between the groups until after conception. We can conclude that cows with disturbed rumen metabolism (with low rumen pH) are less likely to conceive. The measurements of reticuloruminal pH may be useful as a predictor of the likelihood of reproductive success, but more research is needed before practical application.