Subcutaneous tissue reaction to polyethylene terephtalate-covered electronic identification transponders in pigs

Polyethylene terephtalate-covered identification transponders were injected in 4 week old piglets to examine clinically and histologically the reaction in the surrounding tissue after 4, 7 and 21 days and 6 months. Inflammatory signs at the injection site were clinically noticed from 2 days onwards and gradually decreased after day 3. A second series of inflammatory events occured in some animals around day 7. Swelling was observed thereafter in a few animals. In the pigs slaughtered at day 4, all samples showed a layer of exudate and debris surrounding the transponder. Afterwards a fibrous capsule developed. The mean thickness of reactive tissue decreased significantly (p < 0.01) between days 4 and 7 and days 14 and 21, and remained unchanged between day 21 and 6 months. The mean (+/- s.e.) capsule thickness was 0.32 +/- 0.12 mm after 6 months. It is concluded that PET-covered transponders are encapsulated in fibrous connective tissue within 3 weeks after injection at the base of the ear. After 6 months the capsule around the transponder revealed no or only minor signs of inflammation.