The use of passive injectable transponders in fattening lambs from birth to slaughter: effects of injection position, age, and breed

A total of 1,159 Tiris half-duplex pas- sive injectable transponders (PIT) of 32-mm length were used to study the electronic identification of 618 fattening lambs of two breeds used for different produc- tion purposes (Ripollesa, meat breed, n = 271, and Man- chega, dairy breed, n = 347). The lambs were s.c. in- jected in the armpit and the retro-auricular positions at 2, 15, and 30 d of age. All lambs were also tagged with a small plastic ear tag after birth. A group of 76 lambs were injected only in the right armpit and were kept for breeding. The PIT losses, breakages, and elec- tronic failures were evaluated at weekly weight re- cordings throughout the fattening period using two types of hand-held transceivers. Fattened lambs were harvested in a commercial abattoir between 3 and 4 mo of age when they reached market weight (11 to 12 kg hot carcass weight). The total number of PIT that fell or broke in the slaughtering line, the location method, and the recovery time were recorded. On the farm PIT losses were not affected (P > 0.05) by age at injection, injection position, or breed. Mean losses of PIT and ear tags during the same period were 5% and 6.3%, respectively (P > 0.05). No PIT breakages or fail- ures were observed during the fattening period. Mean recovery of PIT in the abattoir (85.6%) was affected (P 0.05) by breed, injection posi- tion, or age, thus allowing a harvesting speed of 200 lambs/h on average. In conclusion, the injection of 32- mm PIT into the armpit or the retro-auricular region is not recommended as a practice for the electronic iden- tification of fattening lambs, even though they perform similarly to small plastic ear tags. This is partly a conse- quence of the PIT losses observed on the farm but mainly because of the difficulties with recovering the PIT in the abattoir. More research will determine whether the use of smaller transponders or injection in other positions could improve their performance in fattening lambs.