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The present experiment aimed to investigate (1) the effect of weaning age on rumen fermentation, dietary intake, growth, and rumination behavior at 20 d after weaning in Simmental calves, and (2) the relationship between rumination time measured by the Hr-Tag rumination-monitoring system (Hr-Tag; SCR Engineers Ltd, Netanya, Israel) and rumen fermentation variables. Ten Simmental calves were randomly assigned at birth to be weaned at 45 (early weaning, EW) or 60 d of age (normal weaning, NW). EW calves were offered 6 L of bulk whole milk/d from d 2 to 38 and 3 L/d from d 39 to 45, while NW were offered 6 L of bulk whole milk/d from d 2 to 53 and 3 L/d from d 54 to 60. Individual calf starter intake was recorded daily and average daily gain (ADG) was calculated taken into account the BW at 6 d after weaning and final BW at 20 d after weaning. On d 20 after weaning, samples of rumen fluid were obtained via an esophageal tube. These samples were used to determine pH and volatile fatty acids (VFAs) concentration. Throughout the entire experiment, the Hr-Tag system continuously recorded the rumination time (RT) by Hr-Tag loggers positioned on the left side of the neck. No treatment differences were detected for total VFAs concentration and molar proportion of acetate, propionate, and butyrate (P > 0.05). Overall in the period -25 to 20 d relative to weaning time, daily RT did not differ between NW and EW calves and it increased around weaning in both groups. Hr-Tags revealed no differences in daily RT pattern (2h-RT) during the 3 d before rumen collection, while during the day (24 h) 2h-RT significantly varied overall in both EW and NW groups. Daily RT measured by Hr-Tags positively correlated to pH (r = 0.98; P < 0.001), and negatively correlated to concentration of total VFAs (r = −0.90; P < 0.001), acetate (r = −0.85; P < 0.001), and propionate (r = −0.90; P < 0.001). On the contrary, a positive linear relationship was found between daily RT and the mola

The present experiment aimed to evaluate the potential of the Hr-Tag rumination-monitoring system (Hr-Tag; SCR Engineers Ltd., Netanya, Israel) to describe the variation in rumination activity behavior in pre-weaned calves from 2 until 35 days of age. The study was carried out in a commercial farm and involved 9 Italian Simmental calves (3 females and 6 males). All calves were provided ad libitum access to water and starter throughout the study and were offered 6 L of bulk whole milk/d from an open-bucket starting at day 2 from birth and through 5 weeks. The Hr-Tag system continuously recorded the rumination time (RT) by Hr-Tag loggers positioned on the left side of the neck, and data were summarized in 2-h intervals. RT recorded by Hr-Tag loggers increased (P < 0.0001) through the first 4 weeks, reaching a plateau at wk 5 and the pattern of daily RT was similar along the weeks. Around milk feeding the observed 2-h intervals of RT drastically decreased (P < 0.0001) compared to the 2-h intervals before. These data shed light on the daily pattern of rumination activity in pre-weaned calves, showing a distinct daily behavior, as observable in adult cattle. Data of this study support the use of the Hr-Tag system for studying rumination activity behavior in the pre-weaning phase of calves.