Influence of the dehairing machine in abattoirs on the complete traceability of fattening pigs from birth to post- slaughter
Frank Burose
1), Thomas Jungbluth
2), Michael Zähner
1)1) Forschungsanstalt Agroscope Reckenholz-Tänikon ART, Tänikon, CH-8356 Ettenhausen, Tel.: +41 52 368 33 38, frank.burose@art.admin.ch
2) University of Hohenheim, Institute of Agricultural Engineering, D-70593 Stuttgart
Abstract
Electronic labelling is necessary for automatic, individual tracing of pigs. To ensure unique identification of animals, the label must remain in place until the carcase has been dehaired at the slaughterhouse.
Loss rates and the reliability of an electronic and a plastic ear tag were tested in various dehairing machines. Instances of animals passing one another during carcase dehairing were analysed.
1’028 experimental animals with plastic or electronic ear tags were examined both before scalding and after dehairing of the carcase at five different abattoirs. The loss rate with the electronic ear tag was more than two and a half times greater, at 25.2 %, than with the conventional plastic ear tag (9.7 %). Results for the different abattoirs are very heterogeneous. The abattoir with the fewest lost ear tags had a loss rate of 9.0 %, compared with 31.1 % for the one with the most. The electronic ear tags were fully operational before scalding and after dehairing. Carcases were able to pass one another during dehairing. Out of 98 animals involved in passing, 95 changed position by only one or two places. One animal dropped back by three places, one by four and one by five. Between 0.6 and 28.9 % of the slaughtered animals passed one another at the five abattoirs, according to the dehairing machine design.
The results obtained do not allow all the slaughtered pigs to be clearly identified.
Problem
The Swiss Epizootic Diseases Act requires pigs to be identified by an ear tag at or before weaning from the sow. The presence of the ear tag at the place where the individual animal number is linked to the abattoir data is crucial for pig traceability. This interfaces occurs where the carcase is suspended from the gambrel hook. In modern abattoirs, hoisting takes place following dehairing of the carcase.
The dehairing machine has great potential for ripping ear tags out of pigs’ ears. The machine subjects the carcase, and therefore the ear, to considerable mechanical stress and this can cause ear tags to be lost. Identification of the animal downstream of the dehairing machine, and thus full traceability, then become impossible.
Aim
Loss rates and the reliability of an electronic and a plastic ear tag were tested in various dehairing machines. Instances of animals passing one another during carcase dehairing were analysed.
Method
Piglets from a Swiss breeder had an ear tag affixed between the eighth and the 30th day of life. As well as the official plastic ear tag from the Tierverkehrsdatenbank (Animal Tracking Database) plastic ear tag currently in use, an electronic ear tag was also tested (Fig. 1).
Each animal received only one ear tag.
The fattened pigs were delivered to five different abattoirs for slaughter. At the abattoirs the animals were scalded and dehaired in two successive processes after killing. The presence of the ear tags on the carcases was checked before scalding and after dehairing.
The plastic ear tag loss rate was established visually and the loss rate and reliability of the electronic ear tag was checked visually and with the aid of a portable reader. The ear tag loss rate and reliability were previously documented at various dates during rearing and fattening: ear tag application, weaning of piglets, start of rearing, start of fattening, end of fattening.
Fig. 1: The tested ear tags: plastic ear tag (left) and electronic ear tag (right).
Results
The analysis comprised 1’028 pigs killed at five abattoirs in Switzerland. The size of the 47 groups of pigs for slaughter averaged 27 animals. The largest group consisted of 80 animals and the minimum number of fattened pigs marketed was nine. The pigs were killed in the period from 5th of June to 13th of November 2007. Their average age of life was 184 days.
Ear tag losses
Prior to scalding of the carcases, 972 out of the 1’028 animals were reliably allocated to the experiment by visual checking of the four-digit ear tag numbers (Tab. 1). Of that total, 515 animals had a plastic ear tag and 457 an electronic ear tag. By 56 animals, the ear tag was already missing before scalding of the carcases, and these animals could not be definitely allocated. At the second measuring point, after dehairing of the carcases, there were 221 unmarked animals. These individuals had lost their ear tags during either scalding or the dehairing process that followed immediately afterwards. Loss rates varied considerably between the two types of ear tag. The experimental animals with the plastic ear tag had an ear tag loss rate of 9.7 %, whereas more than one-quarter of the electronic ear tags were lost. Taking the average for all the experimental animals, 17.0 % had lost their ear tag after dehairing of the carcases.
Tab. 1: Ear tag numbers and losses of plastic (TVD) and electronic ear tags (ISO) between scalding and dehairing of carcases.
Unit Total TVD ISO No ear tag
n 1'028 515 457 56
n 1'028 465 342 221
n 56
n 165 50 115
% 17.0 9.7 25.2
Ear tag losses (at the slaughterhouse)
Slaughtered animals (after dehairing) Slaughtered animals
(before scalding)
Ear tag losses (before the slaughterhouse)
The 1’028 animals for slaughter were divided among five abattoirs in percentages of between 12.5 and 30.9 % (Tab. 2). Between 100 and 295 animals identified by an ear tag were examined at each abattoir. The five dehairing machines are of three different makes.
Three abattoirs used the same make of dehairing machine, but a different model.
Between 9.0 and 31.1 % of the ear tags were lost at the five abattoirs. Electronic ear tag losses were considerably greater than losses of conventional plastic ear tags. 125 animals with no ear tag after dehairing were found to have an average ear hole diameter of 12.0 mm.
Tab. 2: Ear tag losses of plastic (TVD) and electronic ear tags (ISO) by abattoir.
Total TVD ISO
n n n n % n % n %
1 161 72 89 50 31.1 13 18.1 37 41.6
2 100 73 27 9 9.0 4 5.5 5 18.5
3 188 80 108 26 13.8 5 6.3 21 19.4
4 295 156 139 54 18.3 17 10.9 37 26.6
5 228 134 94 26 11.4 11 8.2 15 16.0
Total 972 515 457 165 17.0 50 9.7 115 25.2
Slaughter- house
Ear tag losses (at the slaughterhouse)
Total TVD ISO
Slaughtered animals (with ear tag before scalding)
Reliability
Following visual recording of the four-digit animal number on the ear tag, the functioning of the electronic ear tags was checked. Both measurements, before scalding and after dehairing, resulted in one hundred per cent recognition of both types of ear tag at all the abattoirs.
Passing
Passing is defined as at least two animals changing position compared with their original positions, in this study between the two measuring points before scalding and after dehairing. Within 47 groups slaughtered, there were 42 instances of passing involving 98 animals (Tab. 3). These 42 instances of passing were distributed over 14 slaughter groups at all the abattoirs.
Eight different passing situations were described. Most commonly, two animals would change position. This event was noted 34 times. All seven other situations occurred only once or twice. 84 of the 98 animals involved in passing moved one place and eleven moved two places. One animal dropped back by three places, one by four and one by five.
Tab. 3: Characteristics of passing. (* in addition to 1’028 tested pigs, another 247 pigs were analysed)
34 of the 42 instances of passing occurred at two of the five abattoirs. At the two plants concerned, up to seven animals were dehaired at one time. At the other three abattoirs, eight instances of passing were recorded, with two animals changing position in each case.
These dehairing machines processed one to two animals at the same time.
The number of animals involved in changes of position varied between 0.6 and 28.9 % (Tab. 4). At two of the abattoirs, between 17 and 29 % of the animals changed position. The percentage at the other abattoirs ranged from 0.6 to 3.2 %. At one of these, there was only one instance of passing in more than 320 pigs slaughtered.
Tab. 4: Instances of passing by abattoir.
Slaughtered animals n 1'275*
Instances of passing n 42 1 2 3 4 5
n 98
% 7.7 84 11 1 1 1
Animals involved
Changes of position
Number of animals
Tiere zeitgleich in Enthaarungs-
maschine
Tierüber- holungen
n % n n n %
1 187 14.7 2 3 6 3.2
2 159 12.5 5-7 18 46 28.9
3 212 16.6 6-7 16 36 17.0
4 394 30.9 2 4 8 2.0
5 323 25.3 1 1 2 0.6
Schlacht- betrieb
Schlachttiere Involvierte Tiere in
Tierüberholungen
Discussion
Several factors influence ripping out of ear tags from the ear. The size and shape of the ear tag determine the surface that may come into contact with objects. Within the production process these comprise housing and slaughtering equipment. The heterogeneous results for ear tag losses at the different abattoirs show that the place of slaughter and thus the carcase scalding and dehairing equipment play a large part. The flexible plastic ear tags are easily deformed by the effect of heat. That increases the likelihood of an ear tag being pulled or pushed out of the ear. The beaters in the dehairing machine impact upon the carcase and thus upon the ear tag. A beater hitting an ear tag may split it or rip it completely out of the ear.
The difference in ear tag losses between the two kinds of ear tag may be explained by factors such as the size, shape and type of material. The arch-shaped plastic ear tag measures 27 x 34 mm, whereas the electronic ear tag is round and is 27 mm in diameter.
The perforated part of the plastic ear tag has a hard, round cap. The perforated part of the electronic ear tag contains the transponder; it is made from hard plastic and is not flexible.
The post material is flexible in both types of ear tag. Due to its smaller size and the greater flexibility of the round shape, the electronic ear tag can more readily be pulled through the ear hole. The development of a tensile force by the dehairing machine beaters is favoured in the case of the perforated part of the hard plastic electronic ear tag, as against the largely soft perforated part of the plastic ear tag. The constitution of the ear tags and the room thus needed to pass through the ear hole together with the measured average ear hole diameter in the case of missing ear tags indicate that the post of the ear tags slips through the ear.
Visual inspection of the ripped-out ear tags shows that most of the ear tags were removed from the ear in one piece.
The hundred per cent reliability of the electronic ear tags shows that production of these ear tags based on the ISO standard (International Organization of Standardization) is mature.
The design of the dehairing machine is a very significant factor in the occurrence of passing.
Those abattoirs with a large number of passings dehair perceptibly more carcases at the same time than the abattoirs with a low instance of passing. The skin of the carcases is soft and wet on entering the dehairing machine. Most of the bristles are easily removed. The frictional resistance of the carcase is thus very low. If two carcases meet, it is easy for them to slip past each other. The passing situations involving three to five changes of place by a single animal would tend to indicate that these animals were held fast by the equipment while other animals passed them.
Conclusion
The results obtained do not allow all the slaughtered pigs to be clearly identified before and after the scalding and dehairing process at the abattoir. The absence of identification following dehairing in the case of two or more successive carcases makes definite allocation of the animals impossible. Reliable identification of individual animals is likewise not possible in sequences of carcases in which animals processed shortly after one another have no ear tags. The possibility of allocating unidentified animals after dehairing on the basis of their place before scalding is mainly determined by the dehairing machine design and thus by the likelihood of animals passing one another.
