Automatic measurement of rumination activity in lactating cows during summer season.

Available data suggest that rumination is depressed during heat stress. The aim of our trial was to evaluate the effect of high temperatures on rumination time (RT) using innovative system. The Hi-Tag rumination monitoring system used in this study consists of rumination loggers positioned on the neck, stationary readers, and software for processing the electronic records. The system summarizes the RT in 2-h intervals. This study used 60 Italian Friesian cows in mid-lactation, raised in a private herd of 286 dairy cows, and fed TMR once daily. Data were collected during summer and the total daily RT, the daytime and nighttime RT were calculated. Daily minimum, mean and maximum temperature were recorded as well as individual daily milk yield (MY). The data were processed using mixed procedure for repeated measures as well as linear and quadratic regressions using RT as dependent variable and daily temperature, MY and DIM. During the trial two hotter periods (HP) were observed. During HP the daily maximum temperature ranged between 32.8 to 38.1° C and the daily minimum temperature ranged between 19.6 to 24° C. Overall total daily RT was 516 ± 87 min d-1 (281 ± 52 and 234 ± 48 min d-1 during nighttime and daytime, respectively). During HP the total daily RT and the daytime RT were significantly lower than the values observed before and after those periods. Overall MY was 21 ± 7 kg d-1 and daily MY was correlated with the total daily RT (r=0.30; P<0.001). A quadratic effect of daily temperature on total daily RT and on daytime was observed, but not on nighttime RT. The temperature, MY and DIM explain the 10% of the RT variability, highlighting that the decline of the RT was non considerable till to a minimum daily temperature of 18° C and to a maximum daily temperature of 28° C. In conclusion high temperatures impact negatively on RT, thus this effect has to be considered during summer to counteract the greater risk of digestive upsets.