Summary
The aim of this study was to evaluate the results of two different electronic pig identification methods on various closed-cycle fattening farms in Brescia, Bergamo and Modena provinces and to consider the effect of slaughter procedures on ear tag retention. On-farm tests involved the intraperitoneal injection of a transponder into 527 piglets aged 20-30 days using a 5 cm steel needle, and the use of an electronic ear tag in 114 piglets of the same age range. The percentage of reading controls of intraperitoneal transponders varied from 96.8-100%, with recovery of 70% at the slaughterhouse. Retention of electronic ear tags on arrival at the slaughterhouse was 75.43%. Activities performed during the slaughter process resulted in the loss of 4.65% of the electronic ear tags present at the beginning of the slaughter cycle. To evaluate the effect of procedures conducted in the slaughterhouse on ear tag retention, various tests were conducted in an industrial slaughterhouse in Modena province, using a total of 199 ear tags of three different brands. The percentage of ear tags recovered after the slaughter process varied from 89% to 96%.

Keywords
Ear tags, Electronic identification, Pigs, Transponders.