- Email: [email protected]
Individual identification of pigs during rearing and at slaughter using microchips
Livestock Science 180 (2015) 233–236
Contents lists available at ScienceDirect
Livestock Science journal homepage: www.elsevier.com/locate/livsci
Short communication
Individual identification of pigs during rearing and at slaughter using microchips Ann-Sofi Bergqvist a,n, Frida Forsberg b, Christina Eliasson b, Anna Wallenbeck b a Division of Reproduction, Department of Clinical Sciences, Faculty of Veterinary Medicine and Animal Sciences, Swedish University of Agricultural Sciences, SLU, P.O. Box 5054, 750 07 Uppsala, Sweden b Department of Animal Breeding and Genetics, Faculty of Veterinary Medicine and Animal Sciences, Swedish University of Agricultural Sciences, SLU, Uppsala, Sweden
art ic l e i nf o
a b s t r a c t
Article history: Received 20 March 2015 Received in revised form 25 June 2015 Accepted 28 June 2015
Identification of individual pigs is essential for management, traceability, breeding, trading and disease control in commercial pig production. Conventional identification methods used for pigs, such as ear tags and tattoos, are not sufficiently reliable due to losses and code erasing. This study investigated the retention rate, functionality and tissue damage of microchips compared with conventional electronic ear tags and assessed the effects of chip size and pig age at microchip injection. A larger proportion of small (95.2%) than large (82.5%) microchips were readable throughout the rearing period (po 0.031). It was better to inject microchips when the piglets were 9–10 weeks old compared with 1–2 weeks (p¼0.058). Ear tags caused significantly more tissue damage than microchips (p¼ 0.001). However, although microchips met the requirements of an identification system for pigs that is unique, easy to read, does not produce apparent disturbance to the animals and causes minimal pathological changes, the proportion of lost microchips was unacceptably high. Further research on chip type, pig age at marking and marking site is needed to find suitable methods for identification of individual pigs. & 2015 Elsevier B.V. All rights reserved.
Keywords: Swine Ears tags Electronic ID Traceability
1. Background Besides identification of pigs for biosecurity reasons when moving between herds and to slaughter (EU, 2008; SJV, 2013), individual identification is essential in breeding and research (Madec et al., 2001). An efficient identification system should be easy to apply, permanently fitted, low cost, and easy and reliable to read ( 498% readability; ICAR, 2012). The most common identification methods in pigs today are tattoos, ear tags, ear notching and electronic ear tags. These methods are useful for identifying pigs during rearing, but the link between live animal and carcass is often broken in the slaughterhouse. Electronic ear tags with an embedded electronic transponder are becoming more popular, especially for identification of breeding animals. External identification methods are not tamperproof and the losses can be extensive. For ear tags, losses of 5–60% have been reported (Madec et al., 2001; Caja et al., 2005; Babot et al., 2006; March et al., 2007, Santamarina et al., 2007). Pigs may lose their ear tags if they become caught on interior fittings in the pen, on the way to slaughter or be lost at the slaughter line after n
Corresponding author. E-mail address: Ann-Sofi[email protected] (A.-S. Bergqvist).
http://dx.doi.org/10.1016/j.livsci.2015.06.025 1871-1413/& 2015 Elsevier B.V. All rights reserved.
slaughter (Stärk et al., 1998). Moreover, ear tagging can be painful for the pig and lesions with subsequent infections are relatively frequent (Leslie et al., 2010). A novel reliable individual identification method could improve monitoring of production and health through connecting information from the rearing period with information on slaughter performance and slaughter remarks. Such information could also improve phenotyping in breeding evaluation. This study evaluated one such novel method for individual identification in pigs during rearing and at slaughter, namely use of microchips. The aims were to investigate retention rate, functionality and tissue damage with microchips compared with conventional electronic ear tags and to assess effects of chip size and pig age at marking.
2. Methods The pigs used in the study were reared at the Swedish Livestock Research Center, Uppsala, Sweden. The study was approved by the Swedish Ethical Committee of Experimental Animals in Uppsala (Dnr: C166/12 and C381/12). In total, 80 pigs from 10 birth litters entered the study. The
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from the injection and then dissected to find the microchip. The surrounding tissue was macroscopically evaluated for tissue damage (0 ¼no damage, 1 ¼alteration in the connective tissue, 2¼ grey discoloration in surrounding tissue). The ear tag was removed and skin lesions surrounding the hole were evaluated (0 ¼no lesions, 1 ¼partially mild redness, 2 ¼mild swelling, 3¼ swelling of the whole ear, 4¼ severe swelling).
3. Statistical analysis Fig. 1. Small and large microchips with disposable syringe and male and female part of the electronic ear tag, with microchip inside the female part.
piglets came from nine litters of F1 crosses between Yorkshire (dam)-Hampshire (sire) and one purebred Yorkshire litter. All piglets were identity-marked with a tattoo in the right ear on the day of birth or the day after birth, and with a conventional plastic tag including an electronic ear tag (23 mm Combi Es, Stallmästaren, Lidköping, Sweden) (Fig. 1) in the left ear at 4 days of age. All pigs were additionally identity-marked with a microchip subcutaneously injected into the auricle base of the right ear using disposable syringes provided with the microchips. The choice of microchip injection site was based on findings in previous studies (Merks and Lambooij, 1999), and the fact that the ear and microchip can be easily removed from the carcass at the slaughterhouse (Caja et al., 2005). The microchips were injected at 1–2 or 9–10 weeks of age, all by the same veterinarian. All pigs included in the study were checked daily for general health problems or problems in connection with ear marking. Eight pigs from each litter were selected to be injected with a microchip. Three piglets died before weaning at 5 weeks of age and were excluded from the study, which thus included 77 pigs (37 castrates and 40 gilts). Balanced gender groups were formed to compare microchip size and pig age at injection. Two sizes of microchips (different brands) were used: large 2 mmx13 mm microchips (LifeChip, Destron Fearing, Langeskov, Denmark) and small 1.4 mmx8 mm microchips with barbs (MICRO ID Mini, Swevet AB, Sjöbo, Sweden) (Fig. 1). Pig age at microchip injection was varied by injecting early or late in the rearing period. The early group was injected with a subcutaneous microchip at 2–13 days of age (6.9 73.66 days, mean 7Std) and the late group was injected at 64–75 days of age (68.9 73.61 days, Mean 7Std). A total of 18 pigs were injected with small microchips early and 20 with small microchips late, and a total of 19 pigs were injected with large microchips early and 20 with large microchips late. Scanning of microchips and of electronic IDs in ear tags was performed using a HHR 3000 Pro scanner with 10-cm antenna (BioControl, Rakkestad, Norway). If a microchip did not read from the ear, the whole body of the pig was scanned to ensure that the microchip had not migrated to another part of the body. Readability was recorded once a week for the first four weeks after injection and thereafter every second week until slaughter. The pigs were slaughtered at on average 120 kg live weight, at a slaughterhouse connected to the Research Centre. Ears were removed from the carcass at the slaughter line, after bleeding and scalding but before weighing and classification of the carcass. Ears were checked visually for ear tag number, and the readability of the microchip and electronic ID was checked with the scanner. The ears were then paired, placed in individual plastic bags and saved for further examination. Macroscopic evaluation of skin lesions and tissue damage to the ears was performed on the day after slaughter. The readability of the ear tag number, tattoo, electronic ID and microchip was checked again. The ears injected with microchips were first evaluated for skin lesions (0 ¼no lesions, 1 ¼mild swelling) arising
Statistical analysis was performed using the programme Statistical Analysis Systems (SAS) version 9.2. Before statistical analyses, all data on wounds were transformed to a binomial scale with 0 ¼no wounds and 1 ¼wounds. Descriptive statistics were estimated using proc FREQ and proc MEANS. Differences in readability of identity between microchips (right ear) and electronic ear tags (left ear) was analysed with a chi square test in proc FREQ, with each pig being its own control (right and left ear). () Differences in the frequency of readability and incidence of wounds post-slaughter between microchip size, pig age at injection and gender were analysed with a mixed logistic regression model in proc GLIMMIX. For the logistic regression analyses, interactions between the variables and the effect of birth litter were investigated and the following three statistical models developed: Readability of microchip during rearing (% of pigs) ¼Microchip sizeþPig age at injection þ Gender þPig age at injection*Gender þObservation occasion (pig) þe (residual) where microchip (small or large), pig age at injection (1 or 9 weeks), gender and pig age at injection*gender were included as fixed effects and observation occasion (12 times over the growingfinishing period) within pig (subject) was included as a repeated random effect using a binomial distribution and a logit link. Readability of microchip post slaughter (% of pigs) ¼Microchip sizeþPig age at injection þ Gender þPig age at injection*Gender þe (residual) where microchip size, pig age at injection, gender and pig age at injection*gender were included as fixed effects using a binomial distribution and a logit link. Presence of wounds (% of pigs) ¼Microchip size þ Pig age at injection þGender þe (residual). where microchip size, pig age at injection, gender and pig age at injection*gender were included as fixed effects using a binomial distribution and a logit link.
4. Results Microchip size and pig age at injection influenced the proportion of lost microchips as shown for the four combination groups of chip size and pig age at injection in Fig. 2. Logistic regression analysis revealed that a significantly higher proportion (p o0.001) of small microchips (95.2 71.02%, LSM7 SE) were readable throughout rearing compared with large microchips (82.5 7 2.12%, LSM 7SE). Accordingly, there was a significant difference (p ¼0.031) in post-slaughter readability between small (96.0 73.01%, LSM7SE) and large microchips (78.7 77.12%, LSM 7SE). There was a tendency (p ¼0.058) for higher readability throughout rearing of the microchips injected later (93.3 71.50%, LSM 7SE) compared with earlier (87.0 71.63%, LSM 7SE). However, there was no significant difference in readability post slaughter between early and late injection. None of the microchips had migrated to other parts of the body. On average, the proportion of readable microchips post slaughter was 85.7%, while the proportion of readable electronic
A.-S. Bergqvist et al. / Livestock Science 180 (2015) 233–236
Fig. 2. Percentage of pigs with a readable microchip over time (days after injection). Pigs were injected with a small or large microchip, early (1–2 weeks of age) or late (9–10 weeks).
ear tags was 88.3% (difference not statistically significant). A large number of electronic ear tags were lost during the slaughter process, as only 3.9% of the electronic ear tags were lost or unreadable in the days just before slaughter but 11.7% were lost or unreadable post slaughter. There were no significant differences in proportion of lost or unreadable microchips between the genders, with 13.5% of 37 castrates and 15.0% of 40 gilts having lost their microchip at the end of rearing. The incidence of visible wounds on the skin post slaughter was 2.6% at the microchip injection site and 23.4% at the electronic ear tag site (p o0.001).There was no significant difference in wounds due to injection between small and large microchips, between early and late injected microchips or between genders. There were no general health problems among the pigs related to microchip injection.
5. Discussion In this study, a large number of microchips were lost from the auricle base during the first month after injection, confirming previous findings (Caja et al., 2005; Prola et al., 2010). A possible reason for this unacceptably large loss of microchips could be the size of the needle used for injection, which could have allowed the microchip to fall out before the skin had healed (Caja et al., 2005). Microchips injected at 9–10 weeks of age had a significantly higher retention rate than microchips injected at 1–2 weeks of age. Similarly, Lammers et al. (1995) reported that injection at 4 weeks of age is more successful than injection at 10 days of age, due to the larger size of the ear. There was no significant difference in readability between microchips and electronic ear tags. Electronic ear tags can fail due to biting or friction from interior fittings (Babot et al., 2006), but in this study the reason for failure in readability during rearing was in all cases due to the electronic ear tag being lost. There was no difference in microchip readability between rearing and post slaughter. However, losses of electronic ear tags increased from 3.9% in the days just before slaughter to 11.7% post
235
slaughter. A possible reason for these losses is fighting when different groups of pigs are mixed during transportation and at the slaughterhouse. A more likely reason is that the ear tags were damaged or lost at the slaughter line when the carcass was washed and scaled. Although some previous studies have concluded that the auricle base is the best site for subcutaneously injected electronic transponders, others have reported great variation in losses of electronic transponders injected at this site, ranging from 1.6–6.9% (30 mm transponder) (Janssens et al., 1996) to 19.4% (23 mm transponder) (Stärk et al., 1998) and 17.1–72.5% (12–34 mm transponder) (Caja et al., 2005). The auricle base is also an easy site for microchip removal at slaughter compared with intraperitoneal injection. There are reports of increased losses of microchip with greater transponder size in pigs and other species (Caja et al., 2005). Due to product development, the sizes of the commercially available microchips have decreased over the years. Thus the microchip sizes in the present study (13 and 8 mm) are smaller than in previous studies. However, the results of the present study also showed that significantly fewer of the smaller microchips were unreadable or lost. Migrating microchips could potentially be a problem in the food industry. However, our results showed that the microchips did not migrate under the skin. Previous studies on electronic transponders have reported incidence rates of injection site inflammation ranging from 1–2% (Stärk et al., 1998) to 40% (Lammers et al., 1995) and concluded that transponder size and syringe size had an influence on the healing process. In the present study, there were no significant differences in wound incidence between small and large microchips.
6. Conclusions Based on the results obtained here, it can be concluded that today's commercially available microchips are not reliable for identification of individual pigs due to microchip losses during rearing. However, the method may be more reliable when small microchips are used and when the microchips are injected late (10 weeks of age). Losses of electronic ear tags at slaughter were also high, indicating that this is not a reliable method of identification. None of the identification methods studied here met the requirements of 498% readability and thus more research is needed to find a satisfactory method. As regards using microchips for identification, more research is needed on injection method, injection site, pig age at injection and microchip size.
Acknowledgements We gratefully acknowledge the staff at Lövsta Research Center for handling the pigs; Lena Eliasson-Selling, senior animal health officer, for supporting our initial idea for this study; and the Royal Swedish Academy of Agriculture and Forestry (KSLA) for funding the study.
References Babot, D., Hernández-Jover, M., Caja, G., Santamarina, C., Ghirardi, J., 2006. Comparison of visual and electronic identification devices in pigs: on-farm performances. J. Animal Sci. 84, 2575–2581. Caja, G., Hernández-Jover, M., Conill, C., Garín, D., Alabern, X., Farriol, B., Ghirardi, J., 2005. Use of ear tags and injectable transponders for the identification and traceability of pigs from birth to the end of the slaughter line. J. Animal Sci. 83, 2215–2224. EU. 2008. EU directive: Identification and registration of pigs. 2008/71/EG.
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ICAR, 2012. International agreement of recording practices Guidelines approved by the general assembly held in Cork, Ireland, in June 2012. Janssens, S., Rocha, L., Bosschaerts, L., Barbosa, M., Puers, R., Villé, H., Geers, 1996. Implant recovery and tissue reaction in growing pigs following implantation of packaging materials for injectable electronic identification and monitoring devices. Prev. Vet. Med. 25 (3–4), 249–258. Lammers, G., Langeveld, N., Lambooij, E., Gruys, E., 1995. Effects of injecting electronic transponders into the auricle of pigs. Vet. Rec. 136 (24), 606–609. Leslie, E., Hernández-Jover, M., Newman, R., Holyoake, 2010. Assessment of acute pain experienced by piglets from ear tagging, ear notching and intraperitoneal injectable transponders. Appl. Animal Behav. Sci. 127, 86–95. Madec, F., Geers, R., Vesseur, P., Kjeldsen, N., Blaha, T., 2001. Traceability in the pig production chain. Rev. Sci. Tech. Off. Int. Epizoot. 20 (2), 523–537. March, E., Ferri, N., Comellini, F., 2007. Pig identification: comparison of results from injected transponders and electronic ear tags. Vet. Ital. 43, 97–102.
Merks, J., Lambooij, E., 1999. Injectable electronic identification systems in pig production. Pig News Info 11 (1), 35–36. Prola, L., Perona, G., Massimiliano, T., Mussa, P., 2010. Use of injectable transponders for the identification and traceability of pigs. J. Animal Sci. 35, 183–186. Santamarina, C., Hernández-Jover, M., Babot, D., Caja, G., 2007. Comparison of visual and electronic identification devices in pigs: slaughterhouse performance. J. Animal Sci. 85, 497–502. SJV, 2013. Märkning, journalföring och registrering. Swedish Board of Agriculture [2012-10-08]http://www.jordbruksverket.se/amnesomraden/djur/oli kaslagsdjur/grisar/markningjournalforingochregistrering.4. 2b43ae8f11f6479737780001307.html. Stärk, K., Morris, R., Pfeiffer, D., 1998. Comparison of electronic and visual identification systems in pigs. Livest. Prod. Sci. 56 (2), 143–150.
Contents lists available at ScienceDirect
Livestock Science journal homepage: www.elsevier.com/locate/livsci
Short communication
Individual identification of pigs during rearing and at slaughter using microchips Ann-Sofi Bergqvist a,n, Frida Forsberg b, Christina Eliasson b, Anna Wallenbeck b a Division of Reproduction, Department of Clinical Sciences, Faculty of Veterinary Medicine and Animal Sciences, Swedish University of Agricultural Sciences, SLU, P.O. Box 5054, 750 07 Uppsala, Sweden b Department of Animal Breeding and Genetics, Faculty of Veterinary Medicine and Animal Sciences, Swedish University of Agricultural Sciences, SLU, Uppsala, Sweden
art ic l e i nf o
a b s t r a c t
Article history: Received 20 March 2015 Received in revised form 25 June 2015 Accepted 28 June 2015
Identification of individual pigs is essential for management, traceability, breeding, trading and disease control in commercial pig production. Conventional identification methods used for pigs, such as ear tags and tattoos, are not sufficiently reliable due to losses and code erasing. This study investigated the retention rate, functionality and tissue damage of microchips compared with conventional electronic ear tags and assessed the effects of chip size and pig age at microchip injection. A larger proportion of small (95.2%) than large (82.5%) microchips were readable throughout the rearing period (po 0.031). It was better to inject microchips when the piglets were 9–10 weeks old compared with 1–2 weeks (p¼0.058). Ear tags caused significantly more tissue damage than microchips (p¼ 0.001). However, although microchips met the requirements of an identification system for pigs that is unique, easy to read, does not produce apparent disturbance to the animals and causes minimal pathological changes, the proportion of lost microchips was unacceptably high. Further research on chip type, pig age at marking and marking site is needed to find suitable methods for identification of individual pigs. & 2015 Elsevier B.V. All rights reserved.
Keywords: Swine Ears tags Electronic ID Traceability
1. Background Besides identification of pigs for biosecurity reasons when moving between herds and to slaughter (EU, 2008; SJV, 2013), individual identification is essential in breeding and research (Madec et al., 2001). An efficient identification system should be easy to apply, permanently fitted, low cost, and easy and reliable to read ( 498% readability; ICAR, 2012). The most common identification methods in pigs today are tattoos, ear tags, ear notching and electronic ear tags. These methods are useful for identifying pigs during rearing, but the link between live animal and carcass is often broken in the slaughterhouse. Electronic ear tags with an embedded electronic transponder are becoming more popular, especially for identification of breeding animals. External identification methods are not tamperproof and the losses can be extensive. For ear tags, losses of 5–60% have been reported (Madec et al., 2001; Caja et al., 2005; Babot et al., 2006; March et al., 2007, Santamarina et al., 2007). Pigs may lose their ear tags if they become caught on interior fittings in the pen, on the way to slaughter or be lost at the slaughter line after n
Corresponding author. E-mail address: Ann-Sofi[email protected] (A.-S. Bergqvist).
http://dx.doi.org/10.1016/j.livsci.2015.06.025 1871-1413/& 2015 Elsevier B.V. All rights reserved.
slaughter (Stärk et al., 1998). Moreover, ear tagging can be painful for the pig and lesions with subsequent infections are relatively frequent (Leslie et al., 2010). A novel reliable individual identification method could improve monitoring of production and health through connecting information from the rearing period with information on slaughter performance and slaughter remarks. Such information could also improve phenotyping in breeding evaluation. This study evaluated one such novel method for individual identification in pigs during rearing and at slaughter, namely use of microchips. The aims were to investigate retention rate, functionality and tissue damage with microchips compared with conventional electronic ear tags and to assess effects of chip size and pig age at marking.
2. Methods The pigs used in the study were reared at the Swedish Livestock Research Center, Uppsala, Sweden. The study was approved by the Swedish Ethical Committee of Experimental Animals in Uppsala (Dnr: C166/12 and C381/12). In total, 80 pigs from 10 birth litters entered the study. The
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A.-S. Bergqvist et al. / Livestock Science 180 (2015) 233–236
from the injection and then dissected to find the microchip. The surrounding tissue was macroscopically evaluated for tissue damage (0 ¼no damage, 1 ¼alteration in the connective tissue, 2¼ grey discoloration in surrounding tissue). The ear tag was removed and skin lesions surrounding the hole were evaluated (0 ¼no lesions, 1 ¼partially mild redness, 2 ¼mild swelling, 3¼ swelling of the whole ear, 4¼ severe swelling).
3. Statistical analysis Fig. 1. Small and large microchips with disposable syringe and male and female part of the electronic ear tag, with microchip inside the female part.
piglets came from nine litters of F1 crosses between Yorkshire (dam)-Hampshire (sire) and one purebred Yorkshire litter. All piglets were identity-marked with a tattoo in the right ear on the day of birth or the day after birth, and with a conventional plastic tag including an electronic ear tag (23 mm Combi Es, Stallmästaren, Lidköping, Sweden) (Fig. 1) in the left ear at 4 days of age. All pigs were additionally identity-marked with a microchip subcutaneously injected into the auricle base of the right ear using disposable syringes provided with the microchips. The choice of microchip injection site was based on findings in previous studies (Merks and Lambooij, 1999), and the fact that the ear and microchip can be easily removed from the carcass at the slaughterhouse (Caja et al., 2005). The microchips were injected at 1–2 or 9–10 weeks of age, all by the same veterinarian. All pigs included in the study were checked daily for general health problems or problems in connection with ear marking. Eight pigs from each litter were selected to be injected with a microchip. Three piglets died before weaning at 5 weeks of age and were excluded from the study, which thus included 77 pigs (37 castrates and 40 gilts). Balanced gender groups were formed to compare microchip size and pig age at injection. Two sizes of microchips (different brands) were used: large 2 mmx13 mm microchips (LifeChip, Destron Fearing, Langeskov, Denmark) and small 1.4 mmx8 mm microchips with barbs (MICRO ID Mini, Swevet AB, Sjöbo, Sweden) (Fig. 1). Pig age at microchip injection was varied by injecting early or late in the rearing period. The early group was injected with a subcutaneous microchip at 2–13 days of age (6.9 73.66 days, mean 7Std) and the late group was injected at 64–75 days of age (68.9 73.61 days, Mean 7Std). A total of 18 pigs were injected with small microchips early and 20 with small microchips late, and a total of 19 pigs were injected with large microchips early and 20 with large microchips late. Scanning of microchips and of electronic IDs in ear tags was performed using a HHR 3000 Pro scanner with 10-cm antenna (BioControl, Rakkestad, Norway). If a microchip did not read from the ear, the whole body of the pig was scanned to ensure that the microchip had not migrated to another part of the body. Readability was recorded once a week for the first four weeks after injection and thereafter every second week until slaughter. The pigs were slaughtered at on average 120 kg live weight, at a slaughterhouse connected to the Research Centre. Ears were removed from the carcass at the slaughter line, after bleeding and scalding but before weighing and classification of the carcass. Ears were checked visually for ear tag number, and the readability of the microchip and electronic ID was checked with the scanner. The ears were then paired, placed in individual plastic bags and saved for further examination. Macroscopic evaluation of skin lesions and tissue damage to the ears was performed on the day after slaughter. The readability of the ear tag number, tattoo, electronic ID and microchip was checked again. The ears injected with microchips were first evaluated for skin lesions (0 ¼no lesions, 1 ¼mild swelling) arising
Statistical analysis was performed using the programme Statistical Analysis Systems (SAS) version 9.2. Before statistical analyses, all data on wounds were transformed to a binomial scale with 0 ¼no wounds and 1 ¼wounds. Descriptive statistics were estimated using proc FREQ and proc MEANS. Differences in readability of identity between microchips (right ear) and electronic ear tags (left ear) was analysed with a chi square test in proc FREQ, with each pig being its own control (right and left ear). () Differences in the frequency of readability and incidence of wounds post-slaughter between microchip size, pig age at injection and gender were analysed with a mixed logistic regression model in proc GLIMMIX. For the logistic regression analyses, interactions between the variables and the effect of birth litter were investigated and the following three statistical models developed: Readability of microchip during rearing (% of pigs) ¼Microchip sizeþPig age at injection þ Gender þPig age at injection*Gender þObservation occasion (pig) þe (residual) where microchip (small or large), pig age at injection (1 or 9 weeks), gender and pig age at injection*gender were included as fixed effects and observation occasion (12 times over the growingfinishing period) within pig (subject) was included as a repeated random effect using a binomial distribution and a logit link. Readability of microchip post slaughter (% of pigs) ¼Microchip sizeþPig age at injection þ Gender þPig age at injection*Gender þe (residual) where microchip size, pig age at injection, gender and pig age at injection*gender were included as fixed effects using a binomial distribution and a logit link. Presence of wounds (% of pigs) ¼Microchip size þ Pig age at injection þGender þe (residual). where microchip size, pig age at injection, gender and pig age at injection*gender were included as fixed effects using a binomial distribution and a logit link.
4. Results Microchip size and pig age at injection influenced the proportion of lost microchips as shown for the four combination groups of chip size and pig age at injection in Fig. 2. Logistic regression analysis revealed that a significantly higher proportion (p o0.001) of small microchips (95.2 71.02%, LSM7 SE) were readable throughout rearing compared with large microchips (82.5 7 2.12%, LSM 7SE). Accordingly, there was a significant difference (p ¼0.031) in post-slaughter readability between small (96.0 73.01%, LSM7SE) and large microchips (78.7 77.12%, LSM 7SE). There was a tendency (p ¼0.058) for higher readability throughout rearing of the microchips injected later (93.3 71.50%, LSM 7SE) compared with earlier (87.0 71.63%, LSM 7SE). However, there was no significant difference in readability post slaughter between early and late injection. None of the microchips had migrated to other parts of the body. On average, the proportion of readable microchips post slaughter was 85.7%, while the proportion of readable electronic
A.-S. Bergqvist et al. / Livestock Science 180 (2015) 233–236
Fig. 2. Percentage of pigs with a readable microchip over time (days after injection). Pigs were injected with a small or large microchip, early (1–2 weeks of age) or late (9–10 weeks).
ear tags was 88.3% (difference not statistically significant). A large number of electronic ear tags were lost during the slaughter process, as only 3.9% of the electronic ear tags were lost or unreadable in the days just before slaughter but 11.7% were lost or unreadable post slaughter. There were no significant differences in proportion of lost or unreadable microchips between the genders, with 13.5% of 37 castrates and 15.0% of 40 gilts having lost their microchip at the end of rearing. The incidence of visible wounds on the skin post slaughter was 2.6% at the microchip injection site and 23.4% at the electronic ear tag site (p o0.001).There was no significant difference in wounds due to injection between small and large microchips, between early and late injected microchips or between genders. There were no general health problems among the pigs related to microchip injection.
5. Discussion In this study, a large number of microchips were lost from the auricle base during the first month after injection, confirming previous findings (Caja et al., 2005; Prola et al., 2010). A possible reason for this unacceptably large loss of microchips could be the size of the needle used for injection, which could have allowed the microchip to fall out before the skin had healed (Caja et al., 2005). Microchips injected at 9–10 weeks of age had a significantly higher retention rate than microchips injected at 1–2 weeks of age. Similarly, Lammers et al. (1995) reported that injection at 4 weeks of age is more successful than injection at 10 days of age, due to the larger size of the ear. There was no significant difference in readability between microchips and electronic ear tags. Electronic ear tags can fail due to biting or friction from interior fittings (Babot et al., 2006), but in this study the reason for failure in readability during rearing was in all cases due to the electronic ear tag being lost. There was no difference in microchip readability between rearing and post slaughter. However, losses of electronic ear tags increased from 3.9% in the days just before slaughter to 11.7% post
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slaughter. A possible reason for these losses is fighting when different groups of pigs are mixed during transportation and at the slaughterhouse. A more likely reason is that the ear tags were damaged or lost at the slaughter line when the carcass was washed and scaled. Although some previous studies have concluded that the auricle base is the best site for subcutaneously injected electronic transponders, others have reported great variation in losses of electronic transponders injected at this site, ranging from 1.6–6.9% (30 mm transponder) (Janssens et al., 1996) to 19.4% (23 mm transponder) (Stärk et al., 1998) and 17.1–72.5% (12–34 mm transponder) (Caja et al., 2005). The auricle base is also an easy site for microchip removal at slaughter compared with intraperitoneal injection. There are reports of increased losses of microchip with greater transponder size in pigs and other species (Caja et al., 2005). Due to product development, the sizes of the commercially available microchips have decreased over the years. Thus the microchip sizes in the present study (13 and 8 mm) are smaller than in previous studies. However, the results of the present study also showed that significantly fewer of the smaller microchips were unreadable or lost. Migrating microchips could potentially be a problem in the food industry. However, our results showed that the microchips did not migrate under the skin. Previous studies on electronic transponders have reported incidence rates of injection site inflammation ranging from 1–2% (Stärk et al., 1998) to 40% (Lammers et al., 1995) and concluded that transponder size and syringe size had an influence on the healing process. In the present study, there were no significant differences in wound incidence between small and large microchips.
6. Conclusions Based on the results obtained here, it can be concluded that today's commercially available microchips are not reliable for identification of individual pigs due to microchip losses during rearing. However, the method may be more reliable when small microchips are used and when the microchips are injected late (10 weeks of age). Losses of electronic ear tags at slaughter were also high, indicating that this is not a reliable method of identification. None of the identification methods studied here met the requirements of 498% readability and thus more research is needed to find a satisfactory method. As regards using microchips for identification, more research is needed on injection method, injection site, pig age at injection and microchip size.
Acknowledgements We gratefully acknowledge the staff at Lövsta Research Center for handling the pigs; Lena Eliasson-Selling, senior animal health officer, for supporting our initial idea for this study; and the Royal Swedish Academy of Agriculture and Forestry (KSLA) for funding the study.
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