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Retention of different sizes of electronic identification boluses in the forestomachs of sheep^1,2

J. J. Ghirardi^*, G. Caja^*,3, D. Garín, M. Hernández-Jover^*, O. Ribó⁴ and J. Casellas^*

^* Grup de Recerca en Remugants, Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, Bellaterra, Spain; and and Facultad de Veterinaria, Universidad de la Repú blica, Montevideo, Uruguay

	Abstract

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
Twelve types of electronic identification ruminal boluses of different dimensions were used to obtain a model for predicting their retention in the forestomachs of sheep. Boluses (n = 1,662) were made of ceramic materials, and their dimensions varied in o.d. (9 to 21 mm), length (37 to 68 mm), volume (2.5 to 21.0 mL), and specific gravity (0.85 to 3.91). Each bolus contained a half-duplex, standardized, glass-encapsulated transponder (32 x 3.8 mm). Boluses were administered to sheep (n = 1,497) of different ages by using the appropriate balling guns, and their retention under semiintensive conditions was recorded for at least 2 yr. When a bolus was lost, the sheep was rebolused with a heavier bolus. All sheep wore 2 plastic ear tags: one for the official control of health programs and the other for farm use. To determine the anatomical limit for a bolus passing through the gastrointestinal tract, the size of the reticulo-omasal orifice was measured in 46 adult sheep (male, n = 14; female, n = 32) that died by causes not related to bolus administration during the experiment. No signs of disease or growth alteration were detected in the bolused sheep. Total ear tag losses during the experiment period were 7.5% on average. Bolus retention (5 to 100%) varied according to bolus features and age of the sheep, but it showed a plateau after 18 mo. Inadequately dimensioned boluses were regurgitated or passed through the gastrointestinal tract and were excreted with the feces. The diameter of the reticulo-omasal orifice in adult sheep differed between male and female (23.1 and 21.8 mm, respectively; P < 0.01) and was greater than the o.d. of the retained boluses. Retention rate was predicted from bolus weight and volume by a logistic regression (R² = 0.997; P < 0.001). When retention data from the literature (59.0 to 100%) were included in the model, the adjustment was slightly lower (R² = 0.967). As a result, the minimum bolus weight estimated to reach a 99.5% retention rate in sheep varied between 16 and 45 g when volume varied between 3 and 22 mL, for boluses with a specific gravity between 2.0 and 5.2. In conclusion, bolus retention rate in sheep varied dramatically according to their features. For safe and efficient retention of electronic identification boluses in sheep, boluses of small volume and diameter (e.g., <15 mm) with specific gravity and weight greater than 3.0 and 20 g, respectively, are recommended.

Key Words: electronic identification • ruminal bolus • sheep • traceability • transponder

	INTRODUCTION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
The electronic bolus has proved to be a reliable and tamper-proof system for animal identification from birth to slaughter (Caja et al., 1999, 2004; Fallon, 2001; Garín et al., 2003, 2005) and was the most used and efficient device in the European Union IDEA Project on animal identification (Ribó et al., 2003). Bolus dimensions are considered to be a critical factor for retention rate in ruminants (Hasker and Bassingthwaighte, 1996; Caja et al., 1997, 1999; Fallon, 2001). Recently, Ghirardi et al. (2006a) proposed a logistic regression model to estimate retention rate of boluses in cattle. The authors concluded that specific gravity (SG), weight, and volume are key factors determining the effective retention of a bolus in ruminants. Because of implementation of the compulsory Regulation EC 21/ 2004 on electronic identification of sheep and goats, and the use of ruminal boluses as the official identification device in the early genotyping of lambs for scrapie susceptibility, reduced bolus dimensions are considered important by the European sheep industry to allow an early identification of lambs.

No negative effects of application of boluses are reported in adult sheep (Caja et al., 1999, 2003) or in lambs (Caja et al., 1999; Garín et al., 2003, 2005; Ghirardi et al., 2006b). Boluses of optimized and miniaturized design proved to be efficiently retained in lambs from suckling to harvesting (Garín et al., 2005; Ghirardi et al., 2006b). Few data on the retention rate of these mini-boluses in adult sheep are currently available. Features and retention rate of the different boluses referred to in the literature are summarized in Table 1.

	MATERIALS AND METHODS

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The experimental procedures and animal care conditions were approved by the Ethical Committee of Animal and Human Experimentation of the Universitat Autònoma de Barcelona.

Animals and Management

A total of 1,497 sheep of different breeds and productive purposes (dairy sheep: Lacaune, n = 182; Manchega, n = 212; meat sheep: Ripollesa, n = 1,103), belonging to 3 farms and farmed under semiintensive conditions, were used during a period of 4 yr. Sheep were in a semiconfinement system that included grazing approximately 6 h/d on cultivated pastures after which they were kept indoors with hay and concentrate. All dairy sheep (n = 394) and a group of Ripollesa meat sheep (n = 153) belonged to the experimental farm of the S1GCE (Servei de Granges i Camps Experimentals) of the Universitat Autònoma de Barcelona (Bellaterra, Barcelona, Spain).

Lambs (1 to 8 wk of age; n = 527) and adult sheep (1 to 9 yr of age; n = 970) were bolused as described by Ghirardi et al. (2006b) using the appropriate balling guns. All sheep were also tagged with 2 flag-type ear tags made of polyurethane: an official plastic ear tag in the right ear (4.2 g, 3.8 x 4.0 cm; Azasa-Allflex, Madrid, Spain), and a commercial ear tag in the left ear (4.1 g, and 3.8 x 3.5 cm; Rumitag, Esplugues de Llobregat, Barcelona, Spain).

The remainder of the Ripollesa sheep belonged to 3 commercial sheep farms registered in the flock-book of the breed (Ramaderia Castosa, Bigues i Riells, Barcelona, Spain, n = 682; Ramadería Vallmitjana, Taradell, Barcelona, Spain, n = 168; and, Mas Muxach, Torroella de Montgrí, Girona, Spain, n = 100) and were bolused at approximately 3 to 5 mo of age, when they were chosen for replacement, and also tagged with a flag-type official polyurethane ear tag in the right ear (4.2 g, 3.8 x 4.0 cm; Azasa-Allflex). Sheep were bolused by trained operators using the appropriate balling gun according to bolus type (Ref-012, Rumitag). When a bolus was lost, the sheep were bolused again with a heavier bolus as soon as possible after detection.

All sheep that died or were culled during the experiment in the S1GCE experimental farm (n = 56) were sent to the Pathology Service of the Universitat Autònoma de Barcelona for necropsy, and boluses were recovered. Located boluses were removed manually from the reticulorumen by cutting the reticulorumen wall next to the location site. At necropsy, the diameter of the reticuloomasal orifice was measured in a total of 46 adult sheep (male, n = 14; and, female, n = 32) by using a conical caliper calibrated between 5 and 14 mm (with marks every 2.5 mm).

Electronic Boluses and Transponders

Twelve types of cylindrical boluses made of different materials, totaling 1,662 boluses, and varying in dimensions (weight; o.d x length; volume; and SG), were used (Table 2). Seven types were mini-bolus prototypes, of which 4 types were made of alumina (Al₂O₃) according to the patent by the European Community et al. (1998) and Caja et al. (2001), and the other 3 were made of zirconia (ZrO₂) according to the patent of Caja et al. (2005). Three others were standard commercial boluses also made of alumina according to the European Community et al. (1998) and Caja et al. (2001) patents. The last 2 were prototypes made of plastic laboratory tubes filled with concrete and silicone, or made of bars of PVC hollowed out to make enough space to contain the transponder. These boluses were made to increase the experimental range of variation of bolus dimensions; they had a low SG but a similar volume to the standard boluses.

Transceivers and Reading Procedures

Electronic boluses were read throughout the experiment in static conditions, using handheld transceivers (Gesreader 2S ISO, Rumitag) in restrained sheep, or in dynamic conditions, using stationary transceivers F-210 (Rumitag) connected to a left-side-installed antenna (94 x 52 cm; Rumitag) in sheep passing through a runway (width, 40 cm). Both transceiver types were certified by the Tempest laboratory (Korn, 2004) guaranteeing the reading performances (handheld, >22 cm; and, stationary, >65 cm) specified in the technical guidelines for implementation of the Regulation 21/ 2004 in sheep and goats in the European Union (SANCO, 2005). At reading, the transceivers recorded and stored the transponder code and the reading time. Data was downloaded onto a personal computer by using the GesCon v.1.4 software (Rumitag).

Bolus readability was checked by using a handheld transceiver immediately before and after bolus administration to assure that the transponder was functioning and 24 h later in order to record early losses. Bolus administration time was automatically recorded by the handheld transceiver. Static readings were also performed every 3 mo. Data obtained with the handheld reader was used to obtain retention rate, calculated as: (bolus read/bolus administered) x 100. All sheep that died during the experiment were excluded from calculations.

Dynamic readings were also done in the Ganaderia Castosa farm (n = 781) at approximately 1, 2, 3, 5, 10, 13, and 15 mo. When a sheep was not read in dynamic conditions, a handheld transceiver was used to confirm if the bolus was readable in static conditions. Dynamic reading efficiency was estimated as: (bolus read/bolus readable) x 100, according to Caja et al. (1999) and Conill et al. (2000). Lost boluses or failed transponders were not included in the estimation of reading efficiency.

Statistical Analyses

Retention rate data of all boluses was analyzed by means of a nonlinear least squares regression model, using the NLIN procedure of SAS (v.8.2, SAS Inst. Inc., Cary, NC), assuming a logistic distribution, as indicated for bolus retention rate in cattle (Ghirardi et al., 2006a). The model included the weight (W) and volume (V) of the boluses as independent covariates:

where y = bolus retention rate; b₀, b₁, and b₂ = the regression coefficients; and A = the maximum value of bolus retention rate.

The WEIGHT statement was used to assign the relative weight of each value of retention rate according to the number of animals, allowing for a weighted regression. Moreover, to increase the statistical power of the regression model, a meta-analysis, including the independent bibliographical data reported in Table 1, was also conducted.

Dynamic reading efficiency was analyzed using the PROC MIXED procedure of SAS for repeated measures. Statistical significance was declared at P < 0.05, and means were separated with a Tukey’s test.

	RESULTS AND DISCUSSION

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
Bolus Dimensions

Dimensions of mini-boluses ranged between 5.2 and 25.8 g in weight, 9 and 15 mm in o.d., 37 and 56 mm in length, and 2.16 and 3.91 in SG. These dimensions included the previous mini-bolus prototypes used by Garín et al. (2003, 2005) and Ghirardi et al. (2006b) in lambs. Dimensions of the standard commercial boluses varied between 51.4 and 75.1 g in weight, 17 and 21 mm in o.d., 66 and 68 mm in length, and 3.11 and 3.60 in SG. The plastic prototypes varied between 15.6 and 27.4 g in weight, 20.5 and 21.0 mm in o.d., 60 and 68 mm in length, and 0.85 and 1.34 in SG, according to the experimental design. All bolus dimensions are summarized in Table 2.

Bolus Administration and Data Recording

Administration of boluses used in our experiment was done in suckling lambs (n = 394), in replacement ewe lambs before 6 mo of age (n = 192), or in adult sheep (n = 891). Absence of problems at bolus administration were also reported by Caja et al. (1999, 2003) and Stanford et al. (2001) in adult sheep, and Garín et al. (2003, 2005) and Ghirardi et al. (2006b) in lambs, when bolus size was adapted to animal size. Mortality rate of sheep during the experiment was 4.6% on average, equivalent to an estimated annual mortality rate of less than 2%. None of these deaths were related to bolus administration or long-term damages, as concluded from the pathology service reports of necropsy. This mortality rate is lower than the average annual mortality estimated for adult sheep (5%) in Spain (Saa et al., 2005) as well as in international reports (Binns et al., 2002; Walton, 2002).

Total time for bolus administration and data recording, calculated in the farm Ramaderia Castosa with adult sheep restrained in a runway, averaged 33.2 ± 1.5 s. This time was similar to the time reported by Ghirardi et al. (2006b) in suckling lambs. Administration time was greater than the value previously reported by Caja et al. (1999) in adult sheep, who recorded an average of 24 ± 3 s using boluses of 75 g, but without including the restraining time. For practical on-farm conditions, longer bolus administration times were reported on breeding stock of different ages by Caja et al. (2003; 68 s on average) and ADAS (2005; range, 60 to 84 s). The time was considered similar to ear tagging in the British pilot project (ADAS, 2005). A greater total identification time (1 to 3 min) was estimated for restraining and administrating boluses to sheep under a wide range of conditions (intensive to extensive) in the European IDEA Project (Ribó et al., 2003), estimating that the average number of sheep identified daily by a team of 2 operators, is approximately 300.

A total of 1.6% of the sheep identification records showed errors in the manually typed data. These errors were mainly produced when the individual ear tag number was typed on the keyboard of the handheld transceiver. Values were lower than the 6% of errors estimated by Austin (1995) when manual data management was used, but greater than the 0.1% generally attributed to electronic data management. Average manual errors estimated on paper registration in the British sheep pilot study was 5% (ADAS, 2005).

Bolus Retention

Results of bolus retention rate in the forestomachs of sheep during the time of the experiment ranged from 5.0 to 100% (Table 2), depending on bolus type (P < 0.001). Values converged to 100% for the greater bolus dimensions (Figure 1), as previously indicated by Ghirardi et al. (2006a). Retention rate data were satisfactorily predicted by the logistic model assessed using bolus weight and bolus volume as covariates (R² = 0.997; P < 0.001). The estimated regression coefficients were A = 100, b₀ = 0.842, b₁ = 0.485, and b₂ = –0.807. Inclusion of SG in the model did not improve the adjustment and was not considered. This was a consequence of the small range of variation of the SG data used and to that SG expression also implicit contains weight and volume.

View larger version (10K): [in this window] [in a new window]   Figure 1. Bolus retention rates (%) according to their weight and volume (V, mL) in sheep under on-farm conditions (•, observed data, n = 1,662; and , literature data, n = 666). Lines are the predicted retention rate according to the logistic model:

where W the bolus weight (g) and V the bolus volume (mL).

As shown in Figure 1, retention rate increased with bolus weight and decreased with bolus volume, indicating the suitability for miniaturized and heavy boluses in sheep, as previously concluded in cattle (Ghirardi et al., 2006a). Figure 1 also includes the predicted values for the parameterization of the equation at 3, 9, and 22 mL of bolus volume compared with observed values. On average, error of the predicted retention rate values was 1.3 units of percentage (Figure 2).

View larger version (9K): [in this window] [in a new window]   Figure 2. Comparison of observed and predicted values of bolus retention rate in sheep (mean SE = 1.3).

According to these equations, the minimum weight to obtain the desired retention rate for the parameterized volumes of 3, 9, and 22 mL were: 15.3 g (SG = 5.11), 24.2 g (SG = 2.69), and 43.5 g (SG = 1.98). These values are lower than those previously estimated by Ghirardi et al. (2006b) in cattle and similar to the SG range (1.8 to 2.5) accepted as necessary for the retention of therapeutic boluses in calves (Riner et al., 1982; Allen et al., 1985). Although lighter materials can be used for manufacturing sheep boluses when compared with cattle, no plastic polymers reach the requested SG for bolus retention in sheep forestomachs. Special nonmagnetic materials, transparent to the radiofrequency radiation (e.g., ceramic) should be used for producing electronic boluses. Special attention should be paid to the SG of the materials if the aim is to design a mini-bolus capable of being administered to young lambs and efficiently retained in adult sheep. Relationship between bolus volume, weight, and SG is shown in Figure 3, from where it can be concluded that few mini-bolus designs will have a retention rate >99.5% when SG < 3.

View larger version (30K): [in this window] [in a new window]   Figure 3. Bolus weight and volume combinations that allow a retention rate (RR) greater than 99.5% (gray zone), according to bolus specific gravity (SG), in adult sheep on-farm conditions.

Total losses of plastic ear tags throughout the experiment were 7.5% on average (3.3% annual rate), without differences between farms (P > 0.05). A total of 4 sheep lost both ear tags and the ears of 6 other sheep appeared split and unsuitable for retagging. The ear tag annual losses observed in our data were low, when compared with the range of values (6.3 to 11.4%) reported in the literature (Conill et al., 2002; Caja et al., 2004). In a recent pilot study on use of electronic identification and electronic data transfer carried out in the British sheep industry (ADAS, 2005), ear tag losses ranged from 2 to almost 9% in breeding stock (but reached 42% on 1 farm), which are unsatisfactory according to the ICAR (2005a) recommendations (>99% for 6 mo; >98% for 12 mo).

Bolus Automatic Reading

Handheld transceivers used in our experiment read all boluses present in sheep at any age (readability, 100%). The best reading results were obtained when sheep were individually restrained and scanned in the left side armpit area (location of the reticulum), although some boluses were read when scanned caudo-ventrally on the right side (position of the blind caudo-ventral sac). With regard to the static transceiver used to evaluate the dynamic on-farm reading efficiency in 8 reading controls performed with a total of 792 sheep (6,036 readings), values ranged between 95.9 and 100% (Table 3) and were 98.5% on average. The lowest reading efficiency values were obtained with the mini-bolus of 16 g (12.2 x 42.2 mm), and overall mean increased to 99.6% when it was excluded from the calculations. This value is in the range of reading efficiency (99 to 100%) reported by Caja et al. (1999), Conill et al. (2000), and Ghirardi et al. (2006a) in electronically identified cattle. Lower reading efficiency is expected in sheep compared with cattle as a consequence of the faster running speed (1 to 2 sheep/s) and the smaller distance between sheep (and transponders) when passing through a race way. Moreover, Ghirardi et al. (2006b) observed in lambs that mini-boluses of 16 g (12.2 x 42.2 mm) were more often located in the rumen and abomasum than other mini-boluses, which must increase reading difficulties of this type of mini-bolus.

Only boluses from sheep belonging to the S1GCE experimental farm, and necropsied in the Pathology Service of the Universitat Autonoma de Barcelona, were recovered. Location of boluses in the forestomachs was not affected by the bolus type (P = 0.43) or by the breed (P = 0.65); 79.2% were found in the reticulum and 21.8% in the rumen. No boluses were found outside the reticulorumen in the adult sheep necropsied. Values measured for the diameter of reticulo-omasal orifice in the forestomachs of male and female sheep were 23.12 ± 0.11 and 21.83 ± 0.13 cm, respectively, the differences between sexes being significant (P < 0.01). Our results agree with the value (24 mm) previously reported in sheep (Buéno, 1975). The diameter of the reticulo-omasal orifice was greater than the diameter of the retained boluses (15 to 21 mm) as previously reported in cattle (Ghirardi et al., 2006a).

In conclusion, identification performances of boluses in sheep varied dramatically varied according to their features. For effective bolus retention in the reticuloru-men of sheep and an efficient automatic reading, bolus design should be optimized taking into account weight, volume, and SG.

	IMPLICATIONS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 
Weight and volume are key dimensions for retention of electronic identification boluses in the reticulorumen of sheep and to avoid losses by regurgitation or passage through the reticulo-omasal orifice. According to the prediction model obtained, to reach a minimum of 99.5% retention rate in sheep, boluses of small volume and diameter (e.g., <15 millimeters) with specific gravity and weight greater than 3.0 and 20 grams, respectively, are recommended.

	Footnotes

 
¹ Research supported by The European Commission, Fifth Framework Program, Quality of Life and Management of Living Resources, Contract FAIR 5 QLK1-2001-02229 EID+DNA Tracing (Electronic Identification and Molecular Markers for Improving the Traceability of Livestock and Meat). Available on http://www.uab.es/tracing/

² The authors appreciate the assistance of R. Costa and the crew of the S1GCE (Servei de Granges i Camps Experimentals) de la Universitat Autònoma de Barcelona, and J. Castosa (Ramaderia Castosa, Bigues i Riells, Barcelona, Spain) for feeding and taking care of the animals; I. Llach (Universitat Autònoma de Barcelona) and R. Bach (Associació Nacional de Criadors d’ovins de raça Ripollesa, Monells, Girona, Spain) for assisting in the on field recordings; J. F. Vilaseca of Rumitag (Esplugues de Llobregat, Barcelona, Spain) and the Subdirección General de Ordenación de Explotaciones del Ministerio de Agricultura, Pesca y Alimentación of Spain (Madrid, Spain) for the supply of part of the electronic boluses and N. Aldam for the English revision of the manuscript.

⁴ Current address: Animal Health and Animal Welfare Unit, European Food and Safety Authority, Largo Palli Natale 5/A, I-43100 Parma, Italy.

³ Corresponding author: gerardo.caja{at}uab.es

Received for publication March 20, 2006. Accepted for publication May 16, 2006.

	LITERATURE CITED

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION IMPLICATIONS LITERATURE CITED

 


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