Proximity sensors attached to ewes and rams at mating can predict date of lambing

<b>Context</b>: Determining the birth date of lambs is important, as it is used in analysis for the generation of breeding values for lamb liveweight and lamb growth traits.<b>Aims</b>: We used proximity sensors to measure the daily interactions between 300 ewes and three rams over the mating period for two successive trial years to test the hypothesis that lambing date can be predicted for a typical New Zealand commercial mating system.<b>Methods</b>: The day that the ewe had the highest number interactions with the three rams was used to estimate the day of conception.<b>Key results</b>: In both trial years, 89% of ewes had a proximity sensor-based predicted lambing date ±6 days of the measured lambing date. In the two trial years, 81% and 78% of ewes had a predicted lambing date ±3 days of the measured lambing date. This demonstrates that the performance of the proximity sensor-based method to predict the lambing date was consistent between years.<b>Conclusions</b>: Proximity sensors, therefore, provide an indirect method to study mating behaviour that can be used to predict the birth date of lambs.<b>Implications</b>: This tool can be used by breeders to improve the breeding values of sires for lamb growth and liveweight when lambs are not tagged at birth, and the management of ewes by grouping them together by gestational age.