Evaluation of migratory distance of passive transponders injected in different body sites of adult sheep for electronic identification

To study the effect of injection body site on migration and readability of transponders in sheep, 153 glass encapsulated passive transponders (Tiris, 32.5 x 3.8 mm) were subcutaneously injected in 26 ewes by a trained operator. Six body regions were considered: ear base, neck, chest, armpit, groin and tail. Ease of injection and animal reactions were also evaluated. The injection point was marked afterwards with a surgery clamp. Animals were radiographed at 15, 45, 90 and 180 d post-injection, and migration distance from the injection point was evaluated. A random sample of ten animals was also radiographed at 250d. Migration increased significantly with time in neck, chest and groin. Ear base (34 mm; 6 to 149), and tail (27 mm; 5 to 100), showed the lowest mean and variation intervals from 15 to 180 d. Values were higher in armpit (41 mm; 5 to 150), chest (42 mm; 7 to 218) and groin (43 mm; 7 to 118). The highest values were observed in neck (63 mm; 5 to 209). Mean values at 250 d were unchanged when compared with 180d. Injection site also affected the readability of transponders when losses (tail, 5), breakage tear base, 1; and tail, 1) and migration out of the injection region (neck, 10; ear base, 1; and chest, 2) were considered. Advantages and drawbacks of injection at each body site are discussed. The results suggest firstly armpit, and secondly ear base, as suitable subcutaneous injection sites for electronic identification of Sheep.