The aim of the study was to find the effect of daily diet change from the start of lactation diet (SL) to the peak of lactation diet (PL) taking account into the lactation number (2nd lactation – groups S2L, P2L; 3rd lactation – groups S3L, P3L) using continuous monitoring of ruminal pH using e-bolus at school experimental farm in Oponice. Animals (7 Holstein cows) were fed once with Total Mix Ratio ad libitum (between 4:00 and 5:00) and milked 3 times per day (6:00, 12:00 and 18:00). The bolus which was implemented through Esophagus measured pH and temperature values every 15 minutes (96 data points per day) with accuracy ± 0.1 pH. Data were downloaded and collected with HathorHBClient v. 1.8.1 and statistically evaluated with IBM SPSS v. 20.0 (One-way ANOVA, Tukey Test, Indipendent Samples T-Test). The statistically significant difference (0.74%; P < 0.01) in the daily pH mean between SL and PL diet was found. Dairy cows in the SL group had average pH 6.30 ± 0.34 and in the PL group 6.25 ± 0.33. The daily pH mean of dairy cows in the 2nd lactation 6.45 ± 0.28 (S2L), 6.39 ± 0.25 (P2L) and in the 3rd lactation 6.14 ± 0.32 (S3L), 6.14 ± 0.34 (P3L) was determined. In the S3L (1.12 ± 1.20%) and P3L (1.19 ± 1.19%) group faster decrease of pH values during 6 hours after feeding than in the S2L (0.75 ± 0.41%) and in the P2L (0.55 ± 0.34%) group was found. During night better recover ability of pH values in the S3L (1.62 ± 0.88%) and P3L (2.10 ± 0.90%) group than in the S2L (1.00 ± 0.57%) and in the P2L (1.11 ± 0.70%) group per hour was observed. Overall 8.9% of measured pH under 5.8 in the SL group and 11.9% in the PL group was found. The S2L group had pH under the threshold 5.8 from measured values 1.6% and P2L group only 1.1%. On the other side the pH values in the S3L group formed 16.3% and in the P3L group 20.8%.
