Use of a digital passive infrared motion detector in piglet rearing for the identification of animal activity

Abstract

The activity of pigs is an important indicator of animal welfare and is useful as an input parameter of an early warning tool for behavioural changes caused by e.g. suboptimal housing conditions or health issues. Methods for activity monitoring include video analysis of human observations (V_HO) and dynamic background subtraction (V_BG) or passive infrared motion detectors (PIR). This study analyses the relationship between these methods at the beginning and end of piglet rearing in two different housing environments. Thus, the aim of the present study was to determine whether the representation of activity within a pen using V_BG or PIR, above the activity area (PIR_AA) and the faeces area (PIR_FA), is comparable to V_HO. The trial used data from video analysis (V_BG and V_HO) and PIR (PIR_AA and PIR_FA) at the ninth and tenth day (T1) as well as at the 44th and 45th day of piglet rearing (T2) in two barren pens (28 pigs per pen) and two enriched pens (18 pigs per pen). Spearman's rank correlation coefficient (RS) was calculated to determine the correlation between V_HO and V_BG to PIR above the activity area as well as faeces area for each period (T1, T2) and pen. In comparison with V_HO, V_BG showed a RS of 0.94 to 0.96, PIR_AA showed a RS of 0.75 to 0.94 and PIR_FA showed a RS of 0.81 to 0.96. When comparing with V_BG, PIR_AA showed a RS of 0.79 to 0.90 and PIR_FA showed a RS of 0.86 to 0.93. In a further comparison, the number of active phases per method was identified according to the median per method, pen and period. The number of active phases documented by V_HO compared to V_BG and PIR (PIR_AA and PIR_FA) was determined using a regression analysis. In the detection of active phases from V_HO to V_BG, PIR_AA and PIR_FA, V_BG and PIR_AA showed good accuracy (V_BG R² = 0.94, Slope = 1.02; PIR_AA R² = 0.89, Slope = 0.97). Therefore, V_BG and PIR_AA are suitable methods to determine activity in a pen.