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A field study was conducted on a 2,300-sow piggery in southwestern New South Wales, Australia, over a 17-wk period (from weaning at 4 wk of age) to assess the suitability for lifetime traceability of weaners of 4 identification devices: 1) full duplex ear tag (FDX, AIlfiex), 2) half duplex ear tag designed for cattle (HDX, Leadertronic), 3) conventional ear tag (Leader), and 4) ear tattoo (Ketchum ear tattoo 101). Visual read- ability, retention rate, electronic failures, and adverse side effects were assessed at 8 wk after application at both sites and before slaughter at 14 or 17 wk after application at site A and site B, respectively. A total of 394 weaner pigs were randomly assigned after weaning to 6 treatment groups and reared either in small groups in intensive, indoor, concrete-based pens (n = 224; site A) or in a large group on deep litter (n = 170; site B). Visual readability was similar for all ear tag types before slaughter (P > 0.05); however, visual readability of the ear tattoo was lower (P < 0.05), with between 78.2 and 60.0% illegible due to ink fading. Few tags were lost in the 8-wk period after application; however, tag loss increased for each tag device after this period and varied with housing system. Conventional tag loss was greater among pigs housed at site A (29.0%) than in pigs housed at site B (4.9%) in the 6- to 9-wk period before slaughter. The overall readability of FDX and HDX tags did not differ (P > 0.05) between sites; how- ever, overall readability of FDX tags at 98.4% was better (P < 0.05) than 71.8% for HDX tags. Tag costs ranged from $0.73 for the conventional ear tag to $2.42 for the HDX ear tag. The identification devices did not induce production-limiting adverse effects after they were applied. Under conditions of this study, FDX electronic ear tags were the most efficacious for lifetime identification of weaner pigs on-farm. [ABSTRACT FROM AUTHOR]