Peripartal changes in reticuloruminal pH and temperature in dairy cows differing in the susceptibility to subacute rumen acidosis

The present study aimed to investigate changes in the reticuloruminal pH and temperature dynamics in periparturient dairy cows. Reticuloruminal pH and temperature measurements were conducted from 7 d before until 8 d after parturition using indwelling sensors. Nine Simmental and 4 Brown Swiss dairy cows were fed a close-up total mixed ration (52.5% neutral detergent fiber, 5.68 MJ of net energy for lactation per kg of dry matter) with additional 1 kg/cow per d concentrate mixture (29.5% neutral detergent fiber and 6.25 MJ of net energy for lactation per kg of dry matter), starting from 2 wk before the estimated calving date. Postpartum, all cows had free access to the same close-up diet and were gradually fed increasing amounts of a concentrate-rich total mixed ration for early-lactation cows (32.7% neutral detergent fiber, 7.22 MJ of net energy for lactation per kg of dry matter). Data showed depressed reticuloruminal pH early postpartum, but only in the group of cows defined as subacute ruminal acidosis (SARA) susceptible (n = 8), which had a higher duration time of pH <5.8 (753 ± 82 min/d) compared with SARA-tolerant cows (n = 5; 15 ± 6 min/d). Also, compared with SARA-tolerant cows (112 ± 91 min/d), the SARA-susceptible group showed longer (1,049 ± 75 min/d) duration time of pH <6.0. When compared by breed, mean reticuloruminal pH tended to be lower in Simmental (6.16 ± 0.03) than in Brown Swiss cows (6.25 ± 0.05), but no differences were observed in the duration of pH <5.8 between breeds. Simmental cows produced more milk (30.4 ± 1.2 kg/d) compared with Brown Swiss cows (27.9 ± 1.3 kg/d). Neither total dry matter intake nor milk yield were different between SARA-susceptible and SARA-tolerant groups. However, SARA-tolerant cows consumed greater amounts of the close-up total mixed ration than their SARA-susceptible counterparts, whereas no difference was observed in the intake of the early-lactating total mixed ration between the groups. Reticuloruminal temperature was not affected by breed or SARA susceptibility. Interestingly, the mean reticuloruminal temperature and the time duration of temperature >39.5°C abruptly dropped from d 2 to 1 before calving by 0.35°C and 430 min/d, respectively. In conclusion, the strong inter-animal variation in reticuloruminal pH responses suggests the need for more careful monitoring and differentiated feeding management of cows during the transition period, whereby the SARA-susceptible cows may require particular attention regarding feeding management and diet composition. The abrupt decrease in reticuloruminal temperature the day before parturition may enable this noninvasive method as a management tool for prediction of parturition time.