Proximity sensors provide an accurate alternative for measuring maternal pedigree of lambs in Australian sheep flocks under commercial conditions

Context. Proximity sensors were used recently to determine the maternal pedigree of lambs on a small plot with high accuracy. If this accuracy is maintained under commercial grazing conditions, this method could be a useful alternative to improving genetic gain in sheep, including reproduction traits. Aims. To investigate using proximity sensors to determine the maternal pedigree of lambs and to define the level of interactions required to determine maternal pedigree confidently irrespective of differences in ewe age, lamb age, birth type, paddock size, flock size or stocking rate under commercial grazing conditions. Methods. We compared maternal pedigree determined using the proximity sensors to DNA profiling (n = 10 flocks) and lambing rounds (n = 16 flocks). Ewes (n = 7315) and lambs (n = 8058) were fitted with proximity sensors under normal grazing conditions for each property for 1-3 days. Flocks varied in ewe age (adults, hoggets and ewe lambs), lamb age (up to 100 days old, except for 1 flock), birth type (singles, multiples), paddock size (0.25-320 ha), flock size (37-420 lambs) and stocking rate (2-100 dry sheep equivalents/ha, except for 1 flock). Key results. An interaction ratio of >2 was required for a confident ewe-lamb match (ewe with the most interactions compared with the ewe with the second-most interactions for each lamb). Using this criterion, the average success of proximity sensors at matching a lamb to a ewe was 95% and the sensors were 97% accurate when compared with the pedigree results from lambing rounds or DNA. For lambs matched successfully, over 90% of this success was achieved in the first 7 h and over 99% in the first 20 h. While the success rate of matching a lamb to a ewe was not influenced significantly by ewe age, birth type, paddock size, flock size or stocking rate, the time to achieve sensor success was significantly quicker for singles than for twins and sensor accuracy was significantly higher for smaller paddocks with higher stocking rates. Conclusions. Our results showed that proximity sensors can establish maternal pedigree effectively and accurately across a range of conditions experienced on commercial properties.