Experimental cases of rumen hypomotility

Cases of sudden drop in rumination time (RT) are commonly defined as rumen hypomotility (RH). These events are often due to different causes, such as environmental stress, digestive pathologies, estrus, lameness, etc. The objective of this study was to investigate, in high producing cows, the modifications occurred during RH cases. Overall, 50 RH cases were identified in 40 lactating Holstein cows across 7 different studies. Identified major causes were housing changes (TS, from freestall to tie stall, n = 15) and primary (PY, no apparent other causes, n = 28). Minor causes were lameness (n = 1), mastitis (n = 3), veterinary practices (n = 4) and estrus (n = 2). From each episode, we considered 3 d before (−3, −2, −1) the event, the first and the last day of RH (0) and the first 3 d of recovery (+1, +2, +3). Average RH length was 4.3 ± 0.9 d. Reticular pH (r-pH) was recorded by boluses and RT by collars. All data were statistically analyzed using JMP (v14.3) with a factorial arrangement for time and RH causes (TS and PY) using mixed model procedure, with day as repeated measure. The results showed a dramatic drop in RT (−270 min, from −3 to 0, P < 0.01) with more descendent slope in TS. We confirmed 200 min of RT as threshold of RH. During RH, DMI and milk yield decreased (−3 and –4 kg, from −3 to 0, P < 0.01) with PY as less productive group (−5 kg/d during the entire study). This fact showed how cow subjected to PY-RH were less productive also before the RH cases. In PY group, daily r-pH increased in d −1 and 0 (+0.06, P < 0.05), as daily r-pH st.dev. increased in d0 and a spike of pH below 5.5 was recorded (+40min and +6AUC, P < 0.05). During the recovery period, high variability in all parameters was recorded, depending on the different outcome of the cows. However, DMI and milk yield level was restored faster and completely in TS. In conclusion, PY-RH cases are characterized by anomalies in ruminal fermentation that can be better detected by measuring variation in daily pH, and not just the 5.5 threshold, as reported in literature. This fact is mainly due to the reticular localization of boluses and the peculiarity conditions at that level.