Retinal image recognition for verifying the identity of fattening and replacement lambs1

With the objective of verifying the presumed identity of sheep in a traceability study based on visual ear tags and electronic boluses, retinal image recognition was used as an auditing biomarker on 152 lambs of 2 dairy breeds (Manchega, n=82; Lacaune, n=70). Lambs were identified with temporary ear tags (birth to weaning), and with official ear tags and electronic mini-boluses (weaning to yearling). At 3 mo of age, 58 lambs were recruited for flock replacement, and the rest were transported to a slaughterhouse. Retinal images (RI) and capturing times (CT) were recorded from the left and right eyes of each lamb in duplicate and by the same operator using an OptiReader device (Optibrand, Fort Collins, CO) at 3, 6, and 12 mo of age in 152, 58, and 58 lambs, respectively. The 3-mo RI were used as reference images and to assess operator training and accuracy of the technique. Intra- and inter-age comparisons were made to obtain the matching score (MS; 0 to 100) of pairs of RI from the same eye, using Optibrand's software. Operator skill improved with training sessions, but MS reached a plateau after the sixth session (264 images; MS=93.2 ± 1.5). Values of CT also decreased in trained compared with untrained operators (63 ± 5 vs. 144 ± 15 s, respectively; P 70, which supported 100% lamb traceability. In conclusion, retinal imaging was an accurate technique for auditing the identity of living lambs from weaning to yearling.