The use of passive injectable transponders in fattening lambs from birth to slaughter: Effects of injection position, age, and breed 1,2

The use of passive injectable transponders in fattening lambs from birth to slaughter: Effects of injection position, age, and breed 1,2 C. Conill*, G. Caja* 3, R. Nehring*, and O. Ribó *Unitat de Ciència Animal, Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain and Safeguards and Verification Techniques Unit, Institute for Systems Informatics and Safety, Joint Research Centre, 21020 Ispra, Italy ABSTRACT: A total of 1,159 Tiris half-duplex passive injectable transponders (PIT) of 32-mm length were used to study the electronic identification of 618 fattening lambs of two breeds used for different production purposes (Ripollesa, meat breed, n = 271, and Manchega, dairy breed, n = 347). The lambs were s.c. injected 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 electronic failures were evaluated at weekly weight recordings 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 failures were observed during the fattening period. Mean recovery of PIT in the abattoir (85.6%) was affected (P < 0.05) by breed and injection position. Losses of PIT in the abattoir were greater (P < 0.05) in the Ripollesa breed (18.4%) than in Manchega (10.0%), and for both breeds losses were greater (P < 0.05) in the retro-auricular than in the armpit positions (18.6 vs 10.8%, respectively). The percentage of PIT broken during slaughtering was low (0.3%). The mean recovery times (18 ± 2 s) were not affected (P > 0.05) by breed, injection position, 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 identification of fattening lambs, even though they perform similarly to small plastic ear tags. This is partly a consequence 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. Key Words: Identification, Localization, Sheep, Transponders 2002 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2002. 80:919 925 Introduction 1 Research supported by the European Commission, General Directorate of Agriculture (DG Agri), Program AIR3, Contract AIR 3 PL 93 2304 (Coupling Active and Passive Telemetric Data Collection for Monitoring, Control and Management of Animal Production at Farm and Sectorial Level, 1995 97). 2 The authors appreciate the assistance of R. Costa and the crew of the Servei de Granges i Camps Experimentals (S1GCE) of the Universitat Autònoma de Barcelona for feeding and taking care of the animals; J. F. Vilaseca and O. Aguilar of Gesimpex Comercial S. L. (Barcelona, Spain), for technical support and advising; the Direction and Veterinary teams of the abattoir of Sabadell (Barcelona, Spain) for the harvesting and recovery facilities; and N. Aldam for the English revision of the manuscript. 3 Correspondence: fax +34 93 5811494; E-mail: gerardo. caja@uab.es. Received June 20, 2001. Accepted November 27, 2001. Traditional identification systems for sheep (wool marks, tattoos, ear notches, and plastic or metal ear tags) are unsuitable and make management and performance recording difficult and expensive in large flocks (Jouveau and Potafeux, 1993; Hosie, 1995; Caja et al., 1997). New individual identification methods are necessary to improve the efficacy of selection and disease control programs in the sheep industry (Kimberling, 1994; Caja et al., 1997). Electronic identification using passive transponders (without batteries) can improve the management and recording of farm animals, allowing the automation of routine tasks and reducing time and human errors during the transfer of data in the recording of performance (Caja et al., 1997, 1999b). 919

920 Conill et al. Among the different types of transponder that can be used in livestock (injectable, ruminal bolus, and ear tags) the most studied system has been the passive injectable transponder (PIT). In sheep, as in cattle (Hasker et al., 1992; Lambooij et al., 1999; Conill et al., 2000) and in pigs (Lambooij et al., 1995; Lammers et al., 1995; Stärk et al., 1998), the optimum injection site for the use of PIT is not known. Positions studied in sheep include beneath the scutiform cartilage of the ear (Kimberling et al., 1993; Kimberling 1994; Hunt, 1994), the ear base (Jouveau and Potafeux, 1993), the retro-auricular region caudal to the ear (Marie et al., 1995; Caja et al., 1996, 1998), and other positions to maintain the PIT in the carcass (Caja et al., 1998). No information is available on the effects of breed characteristics in the retention and retrievability of s.c. injected PIT in sheep. The aim of this work was to evaluate the effects of injection position, breed, and age of the animals on the performance reporting and recovery of PIT used for electronic identification of fattening lambs under intensive fattening conditions. Animals Materials and Methods A total of 618 fattening lambs of two different Spanish breeds, Ripollesa (n = 271; wool fiber diameter 23 to 26 m; closed fleece; meat purpose) and Manchega (n = 347; wool fiber diameter, 25 to 28 m; open fleece, dairy purpose), born on the experimental farm of the Universitat Autònoma of Barcelona were used. Animals were randomly assigned after birth to three experimental groups according to age at injection: 2, 15, or 30 d. Lambs were reared by ewes until wk 4 to 6 of age (12 to 15 kg BW) with free access to water, concentrate diet, and straw. After weaning, lambs were moved to fattening pens and fed a commercial concentrate (DM, 87%; CP, 18.5%; fat, 4%; crude fiber, 4%; NDF, 22%, on DM basis; Agribrands Europe-España, Barcelona, Spain) and given ad libitum access to barley straw for the production of the typical Pascual type lamb (11 to 12 kg hot carcass weight) in an intensive fattening system (Torre et al., 1989). The lambs were weighed every week using a portable electronic scale (Allflex FX31, Azasa, Madrid, Spain). Transponders A total of 1,159 half-duplex and read-only glass-encapsulated PIT (Model Ri-Trp-RC2B, Tiris, Texas Instruments, Almelo, The Netherlands) of 32-3.8-mm were injected s.c. in two positions: armpit (right, left, or both) and retro-auricular (right, left, or both). The side of the lamb that was injected at each position was decided randomly. Replacement animals (males and females) were chosen according to their breeding value and only injected in the right armpit (n = 76). All lambs were also identified with a conventional small plastic ear tag on Figure 1. Positions for the s.c. injection of 32-mm glassencapsulated transponders for the electronic identification of young lambs (A: armpit, RA: retro-auricular region). the left ear after birth (Allflex Tip-tag, Azasa, Madrid, Spain). Serial numbers of the PIT used ranged from 5,911,191 to 8,627,392, indicating they had been manufactured by Texas Instruments with a tough, green biocompatible glass of 0.33 mm thickness (Gruys et al., 1993; Caja et al., 1998), increasing their resistance to breakage. Injections Injections were performed by one trained operator and one assistant according to the procedures described by Caja et al. (1998) and Conill et al. (2000). Figure 1 shows injection positions. The armpit injection (Regio axillaris) resulted in the PIT being placed in the space between the thoracic wall and the caudal muscles of the arm (triceps brachii muscle). In the retro auricular (Regio retro-auricularis) injection, the PIT was inserted caudally to the auricular concavity of the ear, in a downward dorsoventral direction, as close as possible to the auricular cartilage (Scapha). A multi-shot injector (Model Riinj-002A, Tiris, Texas Instruments) equipped with a 60-4.8-mm needle (Model Ri-ndl-oo2a) was used for the injection in both positions. The PIT were packed in car-

Injectable transponders in lambs 921 tridges of 10 and immersed in an iodine gel solution (Betadine oplossing, Dagra, The Netherlands) before injection. Another iodine solution (Braunol, B. Braun Medical, Jaén, Spain) was used to disinfect the body site before and to clean the needle after each injection. Farm Readings Each PIT was immediately read after injection by using an intelligent hand-held transceiver with a built-in keyboard and a stick antenna (Portoreader, Insentec, Marknesse, The Netherlands) and the conventional ear tag number and relevant animal data recorded at tagging (age, sex, breed, and observations) were automatically linked to the PIT number. The data were then transferred to a computer and stored in a database (FeogaPro v. 3.0, Díez et al., 1994). Reading performances were evaluated under static conditions as proposed by Caja et al. (1999a) and Conill et al. (2000). Transponder readability (PIT that were read/pit injected) was determined in restrained animals using two types of hand-held transceivers: Portoreader (with memory and two exchangeable stick antennas of 22- and 50-cm length) and Gesreader I (Gesimpex Comercial, Barcelona, Spain; without memory and with a built in antenna and connection to an external stick of 40 cm). In order to ensure the proper reading of the PIT, the stick antennas were located as near as possible to the injection position in all cases. Readability was evaluated weekly at the weight recording throughout the fattening period. Losses, breakages, and other possible problems (infections, injuries, etc.) were checked, and the absence of breakages was ensured by palpation. An electronic failure was assumed when the PIT was considered not broken by palpation but was not readable. Abattoir Readings and Transponder Retrieval Fattened lambs were harvested when they reached marketable weight (11 to 12 kg hot carcass weight) between 3 and 4 mo of age in a commercial abattoir at a harvesting speed of approximately 160 lambs/h. Retention of plastic ear tags was recorded at the start of the harvesting line. Skin removal was performed manually in all cases by trained operators from the abattoir. Reading of PIT was carried out using the two types of handheld transceivers equipped with stick antennas (Portoreader and Gesreader I). The PIT number was read at the start of the harvesting line and the PIT location and recovery were performed at the end of the line, before the release of the carcass. Total PIT losses (fell out or broken) in the line, the PIT location method within each injection area (by sight, palpation, or cutting), and the total recovery time from the carcass or from the head for each injection position were also recorded. Heads were collected in containers after separation from the body to retrieve the PIT injected in the retroauricular region. Hides were also checked using the hand-held transceivers to detect the presence of PIT, and they were manually removed when necessary. The absence of broken or electronically failed PIT in the heads and in the carcasses was ensured by the use of a highly sensitive metal detector (Type GM 17, Gelan, Tiris). All carcasses were inspected by the veterinarian service before release and grading. Statistical Analysis Conventional linear statistical models were not appropriate to study the effects of the experimental factors on losses, breakages, and readability on the farm and losses, breakages, place of location (carcass, hide, or head), and location method (sight, palpation, or cut) due to the dichotomy of the variables. For this reason a Logit model with the estimation method of maximum likelihood (Cox, 1970) was chosen. The CATMOD procedure of SAS (SAS Inst. Inc., Cary, NC) was used, and factors and interactions that were not significant (P > 0.20) were removed from the model. The recovery time in the slaughterhouse was analyzed by analysis of variance using the GLM procedure of SAS and the factors and interactions that were not significant (P > 0.20) were removed from the model. Recovery times were transformed into the inverse of the square according to the Box-Cox transformation method (Draper and Smith, 1981). Statistical significance was declared at P < 0.05 and, following a significant F-test, means were separated using the Tukey test of SAS. Results and Discussion No apparent animal health disorders as a consequence of PIT injections were noted during the weekly postinjection observations. Average daily gain (280 g/d) and gain:feed ratio (1: 3.2) were similar to those obtained during previous fattening trials without electronic identification (Torre et al., 1989; Caja et al., 1999a; Casals et al., 1999). Injection in the armpit was considered by the operators to be easy and safe for all sheep. However, during the injection in the retro-auricular region in very young animals (2 d old), the needle passed through the skin and made a second perforation in 5% (n = 8) of cases. In these cases, it was necessary to repeat the injection in the animals 1 wk later. The identification in food animals using PIT requires the complete recovery of PIT at the end of the slaughtering line, to avoid any risk to the food chain. For this reason, and because in ruminants the head of the animal is separated from the carcass during the slaughter procedure, the auricular region has been one of the most studied positions for location of PIT. The advantage of this region is that PIT can be recovered during the cutting of the ears or during skin removal, reducing the possibilities of PIT residues in the head and carcass. Most current references (Jouveau and Potafeux, 1993; Hunt, 1994) show the results of injection of a small PIT (18-mm length) under the scutulum (Cartilago scuti-

922 Conill et al. Table 1. On-farm readability of 32-mm transponders used for the electronic identification of lambs according to injection position, age at injection, and breed of lambs Armpit Retro-auricular region Item and breed 2 d 15 d 30 d Overall 2 d 15 d 30 d Overall Injected transponders, n Ripollesa 92 86 121 299 59 56 65 180 Manchega 139 133 126 398 102 95 85 282 Overall 231 219 247 697 161 151 150 462 Lost transponders, n (%) Ripollesa 4 4 3 11 (3.7) 2 2 3 7 (3.9) Manchega 8 13 6 27 (6.8) 3 5 5 13 (4.6) Overall a 12 (5.2) 17 (7.8) 9 (3.6) 38 (5.5) 5 (3.1) 7 (4.6) 8 (5.3) 20 (4.3) Readability, n (%) b Ripollesa 88 82 118 288 (96.3) 57 54 62 173 (96.1) Manchega 131 120 120 371 (93.2) 99 90 80 269 (95.4) Overall a 219 (94.8) 202 (92.2) 238 (96.4) 659 (94.5) 156 (96.9) 144 (95.4) 142 (94.7) 442 (95.7) Dead lambs, n (%) 16 10 8 34 (4.9) 7 13 8 28 (6.0) Replacement lambs, n 12 20 44 76 a Injection position effect (P = 0.575). Breed effect (P = 0.210). Injection age effect (P = 0.652). b Readability = (transponders read/transponders injected) 100. formis). Nevertheless, as noted by Nehring et al. (1994a), the PIT size (related to the size of its internal antenna) is an important factor for determining the reading distance. Thus, the use of small PIT, which can be injected under the scutulum of sheep, reduces the dynamic reading efficiency and its usefulness in practical conditions. Therefore, in order to use the 32-mm length PIT it is necessary to find injection positions other than the scutulum. With this aim, the choice of armpit and retroauricular region seems to be adequate, due to the high readability obtained in other species (Merks and Lambooij, 1990; Lambooij et al., 1999; Conill et al., 2000) and in adult sheep (Marie et al., 1995; Caja et al., 1997, 1998). The total losses and readability of PIT on the farm are presented in Table 1. The PIT losses recorded on the farm were not affected by age, position, or breed of the lambs (P > 0.05), and mean loss values were 5%. The mean losses observed in the armpit region were greater than losses reported in adult sheep of 2.3% (Caja et al., 1996), 1.7% (Ribó, 1996), 1.0% (Marie et al., 1995), and 0% (Nehring et al., 1994b; Caja et al., 1998) using the same PIT size and type. This may be a consequence of the injection region size and the behavior of lambs at early ages. Animals less than 2 wk of age may be more curious than frightened (Romeyer and Bouissou, 1992). For this reason, catching 2-d-old lambs was easy and lambs remained calm and close to the operator after injection. The opposite was observed with lambs injected at 15 d of age. These displayed fear and strong reactions during catching, restraining, and PIT injection. As a consequence, these lambs ran away immediately after injection, making the rejection of PIT through the injection hole more probable. The losses obtained with the animals injected at 30 d of age were only slightly greater (P > 0.05) than those observed at 2 d or those reported in adult animals. The 30-d-old lambs, like adult sheep, ran away immediately after injection. The larger size of the injection region in relation to the PIT in the case of adult sheep may also be a factor. In the retro-auricular region, losses were not affected by the age of the lambs at injection (P > 0.05). The mean losses from the retroauricular region (Table 1) were similar to those obtained by Ribó (1996) in adult sheep using the same size and type of PIT. No breakages or failures of PIT were observed during the trial. For this reason, results of readability were complementary to the losses obtained in each position. Probably, the short duration of the trial for each lamb (between 2 and 4 mo) was the main reason for this result. Fattening lambs do not have feed bunks with head lockers or separators, which in the case of adult animals contribute directly to the breakage of PIT in the retroauricular region (Ribó, 1996). Losses of conventional plastic ear tags was 6.3% during the whole experimental fattening period (n = 39), and another 13.8% (n = 85) showed signs of damage from chewing. No significant differences (P > 0.05) were observed between plastic ear tag and PIT losses. The total percentage of PIT that arrived intact at the abattoir in the harvested lambs was 89.6% (n = 414) in the retro-auricular area and 78.8% (n = 549) in the armpit. For these calculations, the PIT lost on the farm (4.3% in retro-auricular area and 5.5% in armpit, P > 0.05), the PIT injected in lambs that died during the fattening period for reasons not related to the injection procedure (4.9% in armpit and 6.0% in retro-auricular area), and the PIT injected in the armpit of replacement ewe lambs (10.9%) were excluded. The percentage of PIT present in slaughtered lambs was 83.1%. General means of PIT lost and recovered in the abattoir are summarized in Table 2. Mean percentages of PIT recovered varied from 82.1% in the retro-auricular area to 90.2% in the armpit, and total losses ranged from 17.9 to 9.8%, respectively. These recovery percentages were affected (P < 0.001) by breed and injection position. Losses in the Ripollesa breed were greater (P < 0.05) than those in the Man-

Injectable transponders in lambs 923 Table 2. Retrievability in the abattoir of 32-mm transponders used for the electronic identification of lambs according to injection position, age at injection, and breed Armpit Retro-auricular region Item and breed 2 d 15 d 30 d Overall 2 d 15 d 30 d Overall Present transponders, n Ripollesa 71 68 76 215 54 53 59 166 Manchega 120 104 110 334 95 78 75 248 Overall 191 172 186 549 149 131 134 414 Lost transponders, n (%) Ripollesa 10 9 14 33 (15.3) b 16 10 11 37 (22.3) b Manchega 9 6 6 21 (6.3) c 17 12 8 37 (14.9) b Overall a 19 (9.9) 15 (8.7) 20 (10.8) 54 (9.8) c 33 (22.1) 22 (16.8) 19 (14.2) 74 (17.9) b Recovery, n (%) Ripollesa 61 59 62 182 (84.7) c 38 43 48 129 (77.7) c Manchega 111 98 104 313 (93.7) b 78 66 67 211 (95.1) c Overall a 172 (90.1) 157 (91.3) 166 (89.2) 495 (90.2) b 116 (77.9) 109 (83.2) 115 (85.8) 340 (82.1) c Mean recovery time, s d Ripollesa 33 ± 9 25 ± 6 27 ± 9 28 ± 8 11 ± 2 14 ± 2 13 ± 1 13 ± 2 Manchega 19 ± 6 17 ± 3 20 ± 4 19 ± 4 c 14 ± 4 14 ± 3 14 ± 2 14 ± 2 b Overall e 24 ± 5 20 ± 3 22 ± 4 22 ± 2 c 13 ± 3 14 ± 2 13 ± 2 14 ± 1 b a Injection position effect (P < 0.001). Breed effect (P < 0.001). Age at injection effect (P = 0.856). b,c Values for each item in the same column within an injection position or in the same row between injection positions having different superscript letters differ (P < 0.05). d Values are means ± SE. e Injection position effect (P = 0.002). Breed effect (P = 0.179). Injection age effect (P = 0.923). chega breed (18.4 vs 10.0%, respectively). Although it is difficult to find an explanation for the differences between breeds, it is probably because of different management according to purpose (meat or dairy), behavior, and hide and wool characteristics. In both breeds, losses were greater in the retro-auricular region than in the armpit, but the difference was only significant (P < 0.05) in the Manchega breed. These results are due to the fact that the retro-auricular region is a cutting zone during the slaughtering procedure. For this same reason 0.7% of PIT injected in the retro-auricular region were found broken. The high mean percentage of losses obtained in the retro-auricular region (17.9%) suggests that injection in this position is not recommended because it does not allow enough traceability of the animal from the farm to the final point of the slaughtering line. Although losses obtained in the armpit were lower (9.8%, P < 0.05) than in the retro-auricular region, this percentage was also too high to recommend the armpit as a suitable position for injection of PIT under practical conditions. Both percentages of recovery in the abattoir are lower than the desired value for practice (99%) recommended by the International Committee for Animal Recording (Geers et al., 1997). These percentages of losses are greater than losses obtained by Conill et al. (2000) in fattening calves, and it is probable that these differences are related to the hide removal procedure. In bovines, hide removal was performed mechanically with manual help and the hide traction force was approximately similar for all animals. However, hide removal in lambs was performed manually and the hide was pulled off with different traction force, depending on the operator. As a consequence, the PIT injected s.c. could easily fall out during the procedure. The presence of macroscopic injuries to the carcasses (armpit region) and head (retro-auricular region) in relation to the injection site was not observed in any cases and, as described by Hunt (1994), transponders appeared to be surrounded by a thin but very resistant fibrous capsule. Mean recovery times of PIT were not affected by breed or age at injection (P > 0.05; Table 2). However, mean recovery times of PIT from the armpit were greater (P < 0.05) than for PIT in the retro-auricular region. For both positions, the recovery times had a marked skewed distribution (Figure 2). The percentage of PIT recovered in less than 10 s were 58.2 and 57.4% and in less than 20 s were 84.4 and 78.8% in the retro-auricular region and in the armpit, respectively. Values increased to 94.4 and 89.1%, respectively, in under 40 s and reached 97.6 and 93.3% during the 1st min. Mean recovery times increased as a result of migrated or deeply injected PIT. Approximately 0.3 and 4.0% of PIT injected in the retroauricular region and armpit, respectively, required more than 2 min to be recovered. These mean recovery times (10 s in 40% of cases) were greater than the recommendations (Caja et al., 1997) for practical conditions in commercial abattoirs. These results suggest the need for research in automatic recovery methods that will allow a faster recovery, in order to facilitate the use of injectable transponders under practical conditions. For these reasons, and taking into account the results obtained, recovery is recommended in all cases after the slaughtering process, either in the offal plant after cutting off the head (retro-auricular region) or at the end of the line (armpit) before the release of the carcasses.

924 Conill et al. Figure 2. Abattoir recovery time of 32-mm transponders injected into the armpit and the retro-auricular region in lambs. Location and distribution of PIT injected in the armpit and in the retro-auricular region according to the recovery method is presented in Table 3. In the armpit, 14.5% were recovered on the internal side of the hide and the remainder (85.5%) were recovered from the carcass. These percentages were not significantly affected by breed (P = 0.785) or age at injection (P = 0.634). Recovery from the hide was easy and quick (< 5 s) and 94.4% of PIT were located by sight. Nevertheless, these results suggest that 14.5% of carcasses lost their identification during the harvesting process, which reduces the utility of the application in the armpit under practical conditions. Similar results were obtained by Nehring et al. (1994b) using the same type of PIT; 14% of PIT injected in the armpit were recovered on the internal side of the hide in adult sheep at slaughter. However, those authors obtained a lower percentage of losses in this position during harvest (4%). The location method of PIT recovery from the carcass was not affected by breed or age at injection. As shown in Table 3, partitioning according to recovery method was approximately 49:45:6 for sight:palpation:cutting, indicating few difficulties in the Table 3. Location and distribution of transponders injected in different positions according to recovery method in the abattoir Armpit Retro-auricular region Item Hide Carcass Head Hide Carcass Transponders present, % 14.5 85.5 63.8 34.7 1.5 Recovery method, % Sight 94.4 48.7 36.8 57.6 94.3 Palpation 5.6 45.3 56.1 42.4 5.7 Cutting 0 6.0 7.1 0 0 process. A total of 4.5% of PIT were recovered by sight between the 6th and 7th rib. This result is probably due to a mistake made during the injection procedure, because the short period of time involved makes migration an unlikely explanation. As described by Caja et al. (1998) in a 6-mo migration trial performed in adult sheep, average migration value in the armpit was 37 mm, with values ranging from 9 to 76 mm. A total of 1.4% of PIT recovered by cutting armpit region muscles needed between 4 and 10 min to be located and recovered. These values are not acceptable under practical abattoir conditions. In the retro-auricular region, a total of 34.7% of PIT were recovered on the internal side of the hide and 63.8% in the head, with no significant effects produced by breed (P = 0.942) or age at injection (P = 0.885). Recovery on the internal side of the hide was made by sight (57.6%) or palpation (42.4%). Partitioning according to recovery method in the head was approximately 37:56:7 for sight:palpation:cutting, respectively. However, these values do not indicate there is a greater recovery difficulty than in the armpit. Moreover, 1.5% of PIT injected in the retro-auricular region were recovered in the cervical region of the carcass, caudally displaced 20 cm from the injection site. This value is greater than expected because of mistakes produced during injection. The mobility of the cervical region may contribute to this higher migration in the retro-auricular region, as indicated by Caja et al. (1998) in adult sheep. Implications The identification of young lambs using 32-mm injectable transponders in the retro-auricular region or in the armpit did not produce any damage to the animals

Injectable transponders in lambs 925 or carcasses. Losses observed on the farm in lambs were greater than those reported in adult animals. Losses observed in the slaughterhouse also were higher than recommendable values for both positions, which makes its use difficult. Location difficulties of transponders in the retro-auricular region and the retrieval of transponders on the internal side of the hide in the armpit region, which does not warrant the complete identification of carcasses, are also unsatisfactory results. Mean recovery times were greater than recommended values for commercial abattoirs. In conclusion, the use of 32-mm passive injectable transponders in lambs at early ages is not recommended for generalized use under practical conditions. More research will determine whether the use of smaller transponders could reduce losses in the same positions. Literature Cited Caja, G., F. Barillet, R. Nehring, C. Marie, C. Conill, E. Ricard, O. Ribó, G. Lagriffoul, S. Peris, M. R. 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