Use of injectable transponders for the identification and traceability of pigs

Individual identification in pigs is a key point for management, traceability and trade control. The aim of this experiment was to study retention rate and functionality of electronic identification systems in pigs, injected in different sites, to evaluate traceability of animals and highlight histopathological alterations of tissues in different inoculation sites. A total of 60 crossbred piglets were used to compare different transponder inoculation sites. One group (15 piglets) was identified only by plastic ear tags; and three groups were identified by passive injectable transponders (PIT) with different inoculation sites. Pigs were slaughtered in two different moments, in order to evaluate injection sites, macroscopically and histologically, either 50 days after injection or at a normal slaughtering weight. In general, no apparent animal health problems were observed the day after the injection or during the control readings performed during the experiment. Intraperitoneal localization gave excellent results in term of readability until the slaughter time. Transponders at the slaughter line were always recovered in the viscera tray because they were found loose in the peritoneal cavity. In some cases, they were found on the carcasses, attached to the peritoneum. In those cases a sample of peritoneal tissue was collected for histological examination. A reparative chronic reaction with moderate and multifocal fibrosis and neoformed vessels associated to multifocal and mild lymphoplasmacytic infiltrate were detected. In one case (6.7%) the transponder was found on the visceral side of the liver and the histological examination highlighted a localized superficial hepatic atrophy by compression. Retroauricolar site of injection gave lower readability results because 2 transponders (13.3%) were no more readable during the first month after injection. No lesions were found with this inoculation site. PIT injected in the perineal region were operative until slaughter time. Recovery procedures at the slaughter house were simple for animals slaughtered at a low weight, but much more difficult in the case of heavy pigs. Moreover, in three cases (20%), PITs were no more in the subcutaneous tissue but they had an intramuscular localization. The histological examination of the muscles revealed a chronic reparative process. In our experiment, injectable transponders in the intraperitoneal position provided the best identification system for pigs. Histopathological examination revealed only local reparative processes in the tissues interested by PIT contact, and no other pathological changes.