Use of an automated walk-over-weighing system to monitor and forecast liveweight in grazing lambs

Aim of the present study was to evaluate the use of a walk-over-weighing (WoW) technology to remotely weigh growing lambs in a pastoral sheep production system and then use these data to predict future liveweight (LW) at different lead times. Thus, an experiment was carried out in a flock of 144 lambs that were grazing freely for a total of 94 days while an automatic WoW system allowed to remotely estimate LW and growth rate of individual lambs daily under these grazing conditions. Data were recorded as each animal entered voluntarily into the WoW platform and walked through it to access water. Daily LW of each animal was used to forecast LW (FW) at 20, 30, 40, 50, and 60 days ahead of any actual day. The accuracy of the FW was assessed using a linear mixed-effects model and Lin’s concordance correlation coefficient (LCCC) with FW as dependent variable and actual observed LW (OW) as independent for each target days, both animal and date were random effects. In total, data from 132 lambs were included in the final dataset which had an average growth rate of 0.25 ± 0.11 kg/d throughout the 93 days of the trial. The FW for the next 20 and 30 days showed substantial agreement with observed weight (LCCC > 0.90). However, FW beyond 40 days was less precise and accurate (LCCC < 0.75). In addition, the LCCC of FW was higher when estimated from the growth rate in the last 14 compared to the last 7 days and late compared to early in the trial. The WoW technology is suitable to monitor LW and growth rate of lambs both in real-time and to predict future LW in commercial farms. Hence, the WoW system can be recommended to help with on-farm decision making of individual sheep