Monitoring liveweight in sheep is a valuable management strategy: a review of available technologies

Liveweight is a widely accepted proxy for the energy status of sheep at a particular point in time. Fleece-and conceptus-free ewe liveweight and liveweight change influence the productivity of the ewe and optimisation may increase whole-farm profitability. Despite this, it is uncommon for producers to monitor ewe liveweight regularly and objectively. The current review discusses why ewe liveweight is important, identifies and assesses available technologies for monitoring sheep liveweight, and highlights future research priorities. The common theme in the literature is that while there are options that could possibly be used to monitor the liveweight of sheep in extensive grazing systems, few of them offer realistic solutions, especially in regard to timeliness of data collection. Thermal and stereo imaging, body measurements and plasma hormonal assays are unlikely to be commercially viable, while visual assessment, although widely practised, offers a surprisingly poor indication of sheep liveweight. Alternatively, assessment of body condition (condition scoring) or fat (fat scoring) offers viable methods of assessing sheep energy status; however, like conventional static weighing, they are performed infrequently and therefore contribute little to the day-to-day tactical management of sheep flocks. Walk-over weighing systems offer a feasible alternative for regular monitoring of sheep liveweight. Such systems are fully automated, and may be operated remotely. Currently, there are challenges associated with monitoring the liveweight of individual animals using such systems and hence there is little commercial opportunity for individual animal management. Mob-based walk-over weighing, which generates flock average liveweight estimates, offers greater potential in the short term, although the technology would benefit from further research and development, primarily to increase the frequency and repeatability of liveweight capture.