Technical note: Evaluation of an automatic system for monitoring rumination time in weaning calves

Rumination time is a relevant marker for health evaluation. The use of rumination monitoring systems can decrease labor costs when measuring rumination time. The objectives of this study were to: i) validate the Hr-Tag rumination monitoring system for estimating rumination time in Zebu calves during the weaning period and to evaluate the Hr-Tag capacity to identify differences in daily rumination patterns during the weaning period. Thirty-two Gyr calves averaging 69 +/- 7.6 kg body weight and 77.0 +/- 4.0 days were used. Calves were fed 4.7 +/- 0.5 L/day of whole milk and ad libitum commercial textured starter ration up to 83 days old (pre-weaning period). During the weaning period (84-86 days old) the same starter was used, but corn silage was also available and only half the milk dose was offered. After weaning (87-92 days old, post-weaning period) only corn silage and starter were used. For the Hr-Tag system validation, the rumination time obtained by Hr-Tag was compared with visual observations at four 2 h intervals (0600 to 0800, 0800 to 1000, 1400 to 1600, and 1600 to 1800 h) at pre- and post-weaning. Two observers were used in all visual evaluations. To compare daily rumination pattern at pre-weaning, weaning and post-weaning, only the Hr-Tag data was used. Rumination time values between observers were highly correlated (rho = 0.956; P < 0.001). Visual and Hr-Tag rumination time did not follow a similar probability distribution (P < 0.001), but they were correlated (rho = 0.702; P < 0.001). The Hr-Tag system overestimated rumination time, mainly when the calves had visual rumination activity close to or equal to zero. The Hr-Tag detected differences in rumination time between weaning periods (P < 0.05). In conclusion, the Hr-Tag system overestimates rumination time in weaning calves, mainly by recording nonexistent rumination. However, the Hr-Tag system recorded rumination values correlated to visual observations and detected differences in rumination activity among weaning periods.