A mobile and automated walk-over-weighing system for a close and remote monitoring of liveweight in sheep

Monitoring bodyweight (BW) is a critical practice used for management purposes (e.g. assessing weight gain, body condition or establishing slaughtering schedules). Measuring BW indoors is relatively easy although time and labor consuming. However, recording BW outdoors may become difficult. The aim of this project was to trial an automated small ruminant weighing prototype using the remote weighing concept of walk-over-weighing (WoW), combined with radio-frequency identification and designed to be light, resistant, transportable and autonomous in energy. The BW is collected as the animal crosses freely over the WoW platform, strategically placed in an obligatory path combined with a small yard containing water and mineral salts as incentives. We studied the system's efficacy in a series of experiments under a range of sheep farming situations (i.e. indoor and outdoor). Time required for achieving individual voluntary passages, the number of daily visits and the proportion of biologically plausible BW records were analysed. The Lin's concordance correlation coefficient (CCC) was used to establish the agreement between WoW records and the gold standard BW measurements (static weighing scale). Our results showed the feasibility of recording BW with free and voluntary passage of sheep with controlled sheep flow over the platform while preventing congestion. After 2-3 weeks of adaptation, 100% of animals crossed daily. Sheep misbehaviour (e.g. speed of passage) can result in spurious values and accounted for many of the larger weight discrepancies. Once outliers were removed, the prediction accuracy of the system and the CCC ranged between 0.89 and 0.98, showing a substantial agreement between the two methods. Using this standalone WoW system, it was possible to record daily individual BW, which may contribute to save labor and time while providing timely information to improve productivity and animal welfare under varying farming conditions.