Discriminating spontaneous locomotor play of dairy calves using accelerometers

GRÖSSBACHER, V., BUČKOVÁ, Katarína, LAWRENCE, A.B., ŠPINKA, Marek a WINCKLER, C. Discriminating spontaneous locomotor play of dairy calves using accelerometers. Journal of Dairy Science, 2020, 103, 1866-1873. ISSN .
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Play behavior is a promising welfare indicator in dairy calves as it decreases in negative situations such as pain or hunger and increases in positive contexts such as in appropriate social environment. However, directly measuring play is time consuming as it is performed in irregular bouts and can be inconsistent over days. To facilitate automatic recording of play, previous studies fitted tri-axial accelerometers to the hind legs of calves, measuring the velocity of movements in large arenas for short durations, and reported high correlations between vertical axis peak duration and the duration of locomotor play. The current study aimed at validating accelerometers for recording spontaneous locomotor play in the calves’ home-pens for longer durations. Data were collected from n = 48 Holstein Friesian calves at either four or eight weeks of age. Acceleration at the vertical axis of the hind leg was recorded at a rate of 1 Hz. One active time period for each calf was randomly selected (mean observation duration ± SD = 34 ± 9 min). From video of the corresponding time period, frequency of locomotor play events consisting of run, turn and buck/buck-kick was recorded using behavior sampling. Combined counts of play events were highly correlated (rp = 0.91) with counts of peaks in acceleration. However, for calves with higher levels of locomotor play, this method underestimated the extent of play. Alternatively, run, turn and buck events obtained from video were transformed into a binary response by one-zero sampling by creating intervals of 10s and then classifying each 10s interval as comprising events of play or not comprising events of play (noplay) . The corresponding accelerometer data for all 10s periods, equaling 10 consecutive readings each, were classified into play or noplay with quadratic discriminant analysis. 79% of periods with locomotor play were correctly classified. Counts of observed play intervals correlated with the counts of play periods from accelerometers at rp = 0.87, but the discriminant analysis consistently overestimated play. In conclusion, accelerometer measurements at 1 Hz (in 1 s intervals) and at the vertical axis alone cannot be used to exactly quantify levels of locomotor play in the home-pen. However, counts of peak accelerations can provide a rough estimate of inter-individual differences in play events and discriminant analysis can be used as a proxy for one-zero sampling of inter-individual differences in locomotor play .

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