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Pre-slaughter handling and pork quality
Meat Science 100 (2015) 118–123
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Pre-slaughter handling and pork quality L. Vermeulen a,⁎, V. Van de Perre a, L. Permentier a, S. De Bie b, G. Verbeke c, R. Geers a a b c
Laboratory for Quality Care in Animal Production, Catholic University Leuven, Bijzondere weg 12, B-3360 Lovenjoel, Belgium BELPORK VZW, Koning Albert II-laan 35, box 54, B-1030 Brussels, Belgium Biostatistical Centre, Catholic University Leuven, Kapucijnenvoer 35, B-3000 Leuven, Belgium
a r t i c l e
i n f o
Article history: Received 5 May 2014 Received in revised form 28 July 2014 Accepted 18 September 2014 Available online 16 October 2014 Keywords: Pre-slaughter stress pH Pork quality Pig
a b s t r a c t Environmental variables, as sound levels, were collected during the pre-slaughter process in 18 different Belgian commercial slaughterhouses. Four pre-slaughter phases were determined: firstly after arrival of the truck at the slaughterhouse and just before unloading, secondly during unloading, thirdly at lairage and finally while moving to the stunner. A total of 8508 pigs was examined during the pre-slaughter process, of which the pHLT (M. longissimus thoracis), at 30 min post-mortem was measured. For each pre-slaughter phase, variables which might influence pork quality were determined. Moreover, this study made it possible to infer a checklist to represent and predict PSE traits of pork for all kind of pre-slaughter situations. The checklist shows also that the impact on pork quality is more decisive for the variables measured close to the stunning phase. Hence, this information is useful for the industry to optimize handling of pigs, reducing the risk for PSE traits. © 2014 Elsevier Ltd. All rights reserved.
1. Introduction Pork production is a still growing industry on the international market (AHDB, 2014), but subjected to great pressure, due to an enhanced competition between export countries. Moreover, consumers still attach a great importance to the trade-off between price and quality but also to the way food is produced, taking into account durability aspects, such as animal welfare (Payne, Mullan, Trezona, & Frey, 1999; USDA-FAS, 2014). Therefore, all stakeholders aim for an optimal qualitative pork production, but too many meat defects still occur, especially Pale Soft and Exudative meat (PSE meat) (Adzitey & Nurul, 2011; Van de Perre, Ceustermans, Leyten, & Geers, 2010; Van de Perre, Permentier, De Bie, Verbeke, & Geers, 2010). PSE meat is caused by acute stress just before slaughter. Pigs genetically sensitive to stress (Halothane gene), but also normal pigs are prone to the defect (Kerth, 2013, chap. 7). Stress results in an accelerated rate of glycolysis. Early post mortem, this metabolism is anaerobic and thus produces lactic acid. A lower pH, due to the lactic acid, while the carcass temperature is still high, results in an increased protein denaturation within the meat (Bendall & Swatland, 1988; Breteler, Wes, Huiskes, Kanis, & Walstra, 1995; Garrido, Pedauyk, Bacon, Lopez, & Laencina, 1995). Due to this process, PSE meat has the property to have a high lightscattering capacity and a low water holding capacity (WHC) (Adzitey & Nurul, 2011; Offer, 1991; Offer & Knight, 1988). Scheffler, Park,
⁎ Corresponding author. Tel.: +32 494281222; fax: +32 16 321994. E-mail address: [email protected] (L. Vermeulen).
http://dx.doi.org/10.1016/j.meatsci.2014.09.148 0309-1740/© 2014 Elsevier Ltd. All rights reserved.
and Gerrard (2011) reported another explanation for the increased pH decline, instead of lactic acid production, namely the free protons and heat, originating from the ATP hydrolysis. To detect PSE meat, the pH of the meat has to be measured 30 min after slaughter. As Josell, Martinsson, Bogaard, Andersen, and Tornberg (2000) defined, the pH value 30 min after slaughter has to be below 6.1. But Van de Perre, Ceustermans, et al. (2010), Van de Perre, Permentier, et al. (2010) and Adzitey and Nurul (2011) reported that in countries where the incidence of PSE meat is high, a stricter pH value (≤ 5.9) can be used. Thereby, handling at the farm, genetics, the season and preslaughter handling, namely during transport, unloading at the slaughterhouse and the handling of the pigs in the slaughterhouse, are very important aspects that influence the stress level of the animal and thus are responsible for the development of aberrant meat quality (Brown, Knowles, Wilkins, Chadd, & Warriss, 2005; Van de Perre, Ceustermans, et al., 2010; Van de Perre, Permentier, et al., 2010). Van de Perre, Ceustermans, et al. (2010) and Van de Perre, Permentier, et al. (2010) listed, described and investigated the combined effect of those parameters. As a follow-up, the significant aspects for the pork quality were selected for each pre-slaughter phase, after which the conditions to comply with good pork quality, were formulated for each pre-slaughter phase. The objective is to build a combination table or checklist for different cases over all pre-slaughter phases which might cause a risk for the pH of the pork and the percentage PSE meat. This table could be very useful for slaughterhouses to evaluate their handling procedures, and if needed to intervene during the preslaughter process to optimize the pork quality.
L. Vermeulen et al. / Meat Science 100 (2015) 118–123
2. Material and methods 2.1. Experimental design In total, 8508 pigs were observed during the pre-slaughter phases, from March 2009 to March 2011 in 18 different slaughterhouses during 2 to 6 visits in each slaughterhouse. The pigs were heterozygous for the halothane or ryanodine receptor gene (Piétrain boar × homozygous negative sow). During each visit, it was attempted to survey two batches of pigs originating from two different farms, which were transported to the slaughterhouse by two different trucks. Pigs of one batch originated from the same farmer and thus had the same unique identification number. In general, pigs in one truck originated from one farm, due to sanitary measures. In total 181 groups of pigs were observed. Nevertheless, if there were pigs from a different batch on one truck, only pigs from one farm were observed. 2.2. Data collection 2.2.1. Pre-slaughter measurements During different phases in the slaughtering process, several influential factors of the pre-slaughter environment were recorded, from transport of the pigs to the moment of slaughtering (Tables 2 and 3). The mean sound level (Testo 815, Testo NV, Ternat, Belgium) (dB(A)) was recorded just before unloading, when the truck arrived at the slaughterhouse, and during unloading. This measurements took place near the truck at the unloading ramp during the whole unloading procedure. The transport time (min), the time elapsing from arrival at the slaughterhouse till start of unloading (min), the mean live weight of the pigs (kg), the total number of panting pigs on the truck, the unique identification number and the stocking density (m2/100 kg) were determined. Furthermore, the duration of unloading, the percentage vocalizing, falling and slipping pigs (%), pigs, having the tendency to turn back during unloading (%) and dead pigs (%) were counted. Unloading aspects, such as the use of a hydraulic lift (yes/no) and the angle of the ramp (°) were recorded. In the pens the number of pigs and the stocking density (m2/100 kg) were quantified, also the presence of drinking nipples (yes/no), of sufficient air flow (yes/no) and of an operational showering system (yes/no) was noted. Also the water temperature of the shower (°C) and the lairage time (min) were registered. During lairage, movement to the stunner and at the stunner, the mean sound level (dB(A)) was recorded, each time at the same place, during 10 min and as close as possible to the group of pigs. The number of slipping or falling pigs (%) during movement to the stunner was counted. Thereby the use of an electrical prod (yes/no) was noted. Finally the stunning method (gas, manual electrical, head-only, head-to-chest), the properties of the used method (CO2 concentration (%) or the voltage (V)) and the stunning efficiency (%), controlled by means of the corneal reflex test, were recorded (Tables 2 and 3) (Van de Perre, Ceustermans, et al., 2010; Van de Perre, Permentier, et al., 2010). 2.2.2. pH measurements The pH (Hanna HI99163, Hanna Instruments, Temse, Belgium) of the M. Longissimus thoracis (pHLT) was measured between the second last and the last rib, 30 min after slaughtering by using a pH electrode of glass (FC232D, Hanna Instruments) enclosed with an unbreakable stainless steel knife, to facilitate the measurements in a muscle. The apparatus was equipped with a built-in temperature sensor to compensate the pH for a change of temperature. At the start of the measurements and after every 20 measurements the pH electrode was treated with a cleaning solution for oils (HI 7077, Hanna Instruments, Temse, Belgium) and a cleaning solution for proteins (HI7073L, Hanna Instruments, Temse, Belgium). Further, the pH electrode was calibrated by using the standard solutions of pH 7 and pH 4. If the pHLT had a deviation of more than 0.01 units, the electrode was recalibrated.
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Due the high speed of the slaughter process, it was not possible to use the referential method of measuring pHLT 45 min after sticking. Therefore the same method for accurate pHLT measurements, recommended by Josell et al. (2000), Van de Perre, Ceustermans, et al. (2010), and Van de Perre, Permentier, et al. (2010) was used, as described in the introduction. pHLT was measured 30 min after sticking. To make the measurements repeatable, the site along the slaughter line, which corresponds to 30 min after sticking, was determined for each slaughterhouse. Those measurements were performed by the same person, using the same type of pH electrode. PSE meat was defined when the pHLT of the pork was less than 6.0, 30 min after sticking. Due to the fact that measurements took place on pigs heterozygous for the halothane gene, a risk to develop PSE meat was higher, as described in the introduction (Brown et al., 2005; Josell et al., 2000; Van de Perre, Ceustermans, et al., 2010; Van de Perre, Permentier, et al., 2010). 2.3. Statistical analysis Statistical model building was conducted with SAS 9.3 software (SAS version 9.3, SAS Inst., Inc., USA). First, the data was checked for normality and univariate analysis was performed (means and standard deviations). The whole pre-slaughter process was split into 4 stages, namely the transport phase, the unloading phase, the lairage phase and the phase at the stunner. Next, the effect of every observed variable (Tables 2 and 3) on the pHLT and the PSE prevalence was examined separately by using a mixed model, whereby slaughterhouse and sampled group of pigs (batch), nested within slaughterhouse, were used as random factors. Only variables classified as significantly (p b 0.05) influencing the pHLT and the PSE prevalence were considered in the model. Correlations between variables were calculated to check for multicolinearity problems. If significant correlations were found between covariates (|r| N 0.6), the most adequate and representative variable was kept in the model. Insignificant variables and variables with less than 80% of the measurements were left out of the model used to build the checklist or combination table. Finally, for every significant variable, criteria were defined to classify from which value the significant variable has a positive or negative effect on the pHLT. If every criteria, for each phase, was performed to ensure a pHLT value, which is considered as indicating no risk for PSE (pHLT ≥ 6), the phase was qualified as ‘Ok’; if not the phase was qualified as ‘Not Ok’ (pHLT b 6). To conclude all this information was merged in one table, whereby combinations of different situations were put together and the remaining pHLT and the potential risks to develop PSE meat (%), for the specific situations, were calculated. 3. Results and discussion In total 181 batches of pigs, containing 8508 pigs, were observed from arrival at the slaughterhouse until stunning, and pHLT was measured. This means an average number of 47 carcasses, randomly selected out of one batch, were examined. Table 1 presents the number of pigs and the number of batches, of which pre-slaughter parameters were observed and post-mortem pHLT was measured per visit, season and slaughterhouse with their respective stunning methods. The frequency distribution of pHLT is shown in Fig. 1, with a minimum pHLT of 5.33, a mean pHLT of 6.19 and a maximum pHLT of 6.95. At European level a prevalence of 8% PSE meat is reported (Kyriazakis & Whittemore, 2006, chap. 2), while this study shows a mean value of 15.10% of the measured carcasses with a high risk for PSE meat, based on pHLT. This difference might be explained by the genotype of the pigs, i.e. 100% heterozygous for the ryanodine receptor gene, being more prone to develop PSE traits (De Smet et al., 1996). Table 2 shows the number of observed pigs and the mean level (±SD) for all observed continuous pre-slaughter variables, subdivided for each pre-slaughter
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Table 1 Number of pigs and number of batches, of which pre-slaughter parameters were observed and post-mortem pHLTe was measured per visit, season and slaughterhouse (plant) with their respectively stunning methods. Number of batchesf
Number of pHLT measurements
Plant 1 Plant 2 Plant 3 Plant 4 Plant 5 Plant 6 Plant 7 Plant 8 Plant 9 Plant 10 Plant 11 Plant 12 Plant 13 Plant 14 Plant 15 Plant 16 Plant 17 Plant 18 a b c d e f
Springa
Summerb
Autumnc
Winterd
Total
Springa
Summerb
Autumnc
Winterd
Totaal
162 61 163 82 173 222 160 100 0 200 181 102 186 100 190 172 0 102
200 200 100 221 100 0 0 63 0 0 0 0 0 100 0 0 150 79
100 201 200 153 201 191 250 200 107 262 300 301 195 150 301 300 0 0
100 50 100 0 100 0 100 90 0 87 100 100 100 200 100 100 200 0
562 512 563 456 574 413 510 453 107 549 581 503 481 550 591 572 350 181
4 2 4 3 4 6 4 2 0 4 4 2 2 3 4 4 0 4
4 4 2 5 2 0 0 2 0 0 0 0 0 3 0 0 3 2
2 4 4 5 4 5 6 4 2 6 6 6 4 4 6 7 0 0
2 1 2 0 2 0 3 2 0 2 3 2 2 4 2 2 4 0
12 11 12 13 12 11 13 10 2 12 13 10 8 14 12 13 7 6
Stunning method CO2 Electrical Electrical CO2 Electrical Electrical CO2 Electrical Electrical Electrical CO2 CO2 Electrical Electrical CO2 Electrical CO2 CO2
Spring: 21 March–20 June. Summer: 21 June–20 September. Autumn: 21 September–20 December. Winter: 21 December–20 March. pHLT: pH of the M. Longissimus thoracis. Batch: Pigs of one batch originating from the same farmer and thus have the same unique identification number.
phase. All class pre-slaughter variables are presented in Table 3 for each pre-slaughter phase with the number of observed pigs and the percent of observations per class. 3.1. Significant variables for each slaughter phase The different significant variables of the global analysis are explained by each phase of the slaughter process after which the checklist is discussed.
3.1.2. Unloading During unloading, both the percentage vocalizing pigs and the mean sound level just before unloading and during unloading had a significant
Percent
3.1.1. Transport A stocking density of 0.41 m2/kg to 0.51 m2/kg on the truck resulted in a significant higher pHLT in comparison with lower or higher stocking densities. As Van de Perre, Ceustermans, et al. (2010), Van de Perre,
Permentier, et al. (2010), Nanni Costa, Lo Fiego, Dall'Olio, Davoli, and Russo (1999) and Guise and Penny (1989) indicated, low stocking densities cause more injuries, because pigs can fall during inconsiderate handling and high stocking densities lead to more fights. Not optimal stocking densities can affect the welfare of the pigs and thus increase the risk for PSE meat. Furthermore, a significant lower risk to develop PSE meat is observed if there were no dead pigs at arrival. So the transport phase is qualified as ‘Ok’ if there are no dead pigs and if the loading density on the truck is between 0.41 m2/kg and 0.51 m2/kg (Tables 2 and 3).
pHLT Fig. 1. Frequency distribution of pHLT.
L. Vermeulen et al. / Meat Science 100 (2015) 118–123 Table 2 Observed continuous, pre-slaughter variables for each pre-slaughter phase, the number of observed pigs (Na), the mean and the standard deviation (SD). Phase
Variable
N
Transport
Before unloading: mean sound level (dB(A)) Transport time (min) Time elapsing arrival–unloading (min) Mean live weight pigs (kg) Panting pigs (%) Stocking density on the truck (m2/100 kg) Dead pigs after transport (%) Unloading Mean sound level (dB(A)) Duration unloading (min) Vocalizing (%) Falling and slipping pigs (%) Turning back (%) Angles of the ramp (°) Lairage Mean sound level (dB(A)) Water temperature of the shower (°C) Lairage time (min) Number pigs in pen Stunning Mean sound level (dB(A)) Falling and slipping pigs (%) If gas stunning: CO2 concentration (%) If electrical stunning: voltage(V)
a
8438
Mean ± SD 73.54 ± 6.22
3421 61.28 ± 46.49 8483 15.13 ± 18.25 8028 115.31 ± 6.17 8483 0.21 ± 0.60 8003 0.44 ± 0.04 4223 0.09 ± 0.29 8376 78.08 ± 3.86 8483 14.37 ± 6.62 8438 4.82 ± 4.06 8438 4.19 ± 5.53 8438 0.54 ± 1.08 8295 6.23 ± 4.39 7983 78.46 ± 4.03 3889 16.46 ± 3.66 8508 100.85 ± 64.16 7745 56.21 ± 40.60 7912 86.09 ± 5.24 8508 0.69 ± 3.27 4024 86.84 ± 5.09 4484 291.49 ± 106.51
N: Number of observed pigs.
3.1.3. Lairage The mean sound level during lairage influenced the risk for PSE meat significantly, and hence has to be lower than 85 dB(A). Also
Table 3 Observed class, pre-slaughter variables for each pre-slaughter phase, the number of observed pigs (Na) and the percent of observations per class. Na
Percent
Yes No
5352 3156
62.91 37.09
Yes No
6153 2355
72.32 27.68
Yes No
8433 75
99.12 0.88
Yes No
3389 4619
45.71 54.29
Yes No
6976 1532
81.99 18.01
Gas Electrical
4024 4484
47.30 52.70
Effective Not effective
5651 2857
66.42 33.58
Variable
Unloading Hydraulic lift (yes/no)
Lairage Drinking nipples (yes/no)
Sufficient air flow (yes/no)
Presence showering system (yes/no)
Stunning Electrical prod (yes/no)
Stunning method
Stunning efficiency: if more than 15% of the pigs are not showing signs of unconsciousness during the corneal reflex test the stunning is not being effective.
a
N: Number of observed pigs.
slaughtering during the winter or autumn makes lairage being classified as ‘Ok’. As Guàrdia et al. (2004), Van de Perre, Ceustermans, et al. (2010), and Van de Perre, Permentier, et al. (2010) stated, high environmental temperatures in summer and temperature fluctuations might result in stress, making it difficult for the pig to maintain deep body temperature, which might result in a poorer meat quality. 3.1.4. Stunning The mean sound levels prior to stunning, the use of an electrical prod (Yes or No) and the quality of the stunning influenced the meat pHLT significantly, as also proven by Van de Perre, Ceustermans, et al. (2010), Van de Perre, Permentier, et al. (2010). But the mean sound level during movement to the stunner was not significant for the PSE risk in this global checklist, due to the multicollinearity with the mean sound level prior to stunning. The stunning phase is classified as ‘Ok’, in case the mean sound level prior to stunning is lower than 85 dB(A), no electrical prod is used and the stunning is effective. In general, this study established that every stage during the preslaughtering process has its impact on the quality of the produced pork. Therefore an overview is set up to indicate whether pigs are having risk to develop PSE meat or not and during which stages of the pre-slaughtering process (3.2). 3.2. Global classification checklist
effect on %PSE. Vocalizing pigs produce high pitched sounds and will activate the pigs' defense mechanism, resulting in stress (Warriss & Brown, 1994). Unloading is classified as ‘Ok’ if the vocalizing percentage is lower than 5%, the sound level just before unloading and during unloading is lower than 85 dB(A).
Phase
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Table 4 shows the effect of different combinations of handling pigs during the four significant stages in the slaughtering process, namely transport, unloading, lairage and stunning phase. The explained variation of this checklist for pHLT is 19.2% and 13.6% for the %PSE meat. The low values does not indicate that X and Y are unrelated, since the model was found to be statistically significant by the F-test, but it can be explained by the number of variables used in this model and the large variability in the dataset (Neter, Kutner, Nachtsheim, & Wasserman, 1996). Thereby some pre-slaughter data of measured carcasses were incomplete, for example when there were no sound levels, measured during lairage due to a technical defect. Thus, those observations were not used in the checklist. A total of 83 batches, meeting the requirements described in each horizontal line, was left to examine the global checklist (3820 carcasses of which the pHLT is measured). Firstly, %PSE was mainly affected by pre-slaughter handling, occurring just before stunning, i.e. the last phase of the handling procedure (Table 4, a, b, c, d, e, f, g, h), resulting in a lower mean pHLT and a higher percentage of loins with PSE traits, compared when the last phase of the pre-slaughter process was performed in terms to deliver good meat quality (Table 4, i, j), as explained in Section 3.1.4 (Van der Wal, Engel, & Reimert, 1999). A good pHLT (6.21 ± 0.08) and a low %PSE (13.53 ± 10.49) were found when only the unloading phase is classified as Ok (Table 4, c). It can be due to the low number of measured batches; thus more observations are required to decide on significant conclusions. Thereby when pigs are stressed during almost the whole slaughtering phase and not, abrupt, at the latest stage of the slaughter process, pigs have less stress then pigs subjected to abrupt, tremendous stress factors, as Kittawornrat and Zimmerman (2010) indicated. This was also proven if both transport, unloading, lairage and stunning procedures were not performed according to the conditions described above (6.13 (± 0.16)) (Table 4, a), comparing with the results if transport and stunning phases were classified as Not Ok (Table 4, g). Stressful periods alternate with stress less periods; thus pigs were more abruptly exposed and created a higher risk to develop PSE meat. Table 4 (d and g) shows that a higher pHLT and a lower %PSE were reported when only lairage was classified as Ok (Table 4, d), compared when also the unloading phase was classified as Ok (Table 4, g). More observations are needed to clarify this result. Thus the global checklist shows the closer in time the preslaughtering phase to the stunning, the more critical the phase in
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Table 4 Mean pHLTk and percentage of PSE meat ± SD (Standard deviation) in different status of transport, unloading, lairage and the stunning itself.
a b c d e f g h i j
Nl
Transport ⁎
Unloading ⁎⁎
Lairage ⁎⁎⁎
Stunning ⁎⁎⁎⁎
pHLTk
%PSEm
9 5 2 3 14 8 6 23 7 4
Not Ok Ok Not Ok Not Ok Ok Ok Not Ok Ok Not Ok Ok
Not Ok Not Ok Ok Not Ok Ok Not Ok Ok Ok Ok Ok
Not Ok Not Ok Not Ok Ok Not Ok Ok Ok Ok Ok Ok
Not Ok Not Ok Not Ok Not Ok Not Ok Not Ok Not Ok Not Ok Ok Ok
6.13 (±0.16) 6.14 (±0.09) 6.21 (±0.08) 6.17 (±0,09) 6.19 (±0.11) 6.19 (±0.09) 6.13 (±0.07) 6.20 (±0.08) 6.27 (±0.08) 6.30 (±0.10)
22.45 (±22.15) 23.69 (±16.44) 13.53 (±10.49) 16.51 (±12.00) 16.70 (14.51) 12.04 (10.74) 24.34 (13.91) 12.60 (11.37) 6.83 (±7.27) 5.13 (±1.00)
a, b, c, d, e, f, g, h, i, j
: References to specific cases, as explained in the text. pHLT: pH of the M. Longissimus thoracis. N: Number of batches, meeting the requirements described in each horizontal line. Pigs of one batch originating from the same farmer and thus have the same unique identification number. m PSE: Pale soft and exudative meat. ⁎ Transport is Ok if there are no dead pigs after transport and the loading density on the truck is 0.41–0.51 m2/100 kg. Otherwise the transport is Not Ok. ⁎⁎ Unloading is Ok if the percentage of vocalizing pigs is less than 5%, mean sound level just before unloading and during unloading is less than 85 dB(A). Otherwise the unloading is Not Ok. ⁎⁎⁎ Lairage is Ok if the mean sound level during lairage is less than 85 dB(A) and the slaughtering took place during the winter or the autumn. Otherwise the lairage is Not Ok. ⁎⁎⁎⁎ Stunning is Ok if the mean sound level prior to stunning is less than 85 dB(A), the use of an electrical prod is not frequent and the stunning is accurate. Otherwise the stunning is Not Ok. k l
terms of developing PSE meat. Thereby, pigs that are not treated in terms of PSE prevalence, as described in Section 3.1, can possibly recover during lairage. This is also proven by the higher mean pHLT of 6.27 (± 0.08) when only transport is classified as Not Ok (Table 4, i). No observations were found when only lairage and stunning were Ok. The highest pHLT was recorded in case every phase was classified under ‘Ok. The better the pre-slaughter conditions, the better the pork quality can be. The resulting %PSE followed the same trend of the mean pHLT. Although 83 batches of pigs were used to perform this analysis, Table 4 shows that this is inconclusive for investigating the relationship of the pHLT over the not mentioned classification-combinations, such as when every phase classified as Not Ok except the transport phase. Therefore more measurements are needed.
4. Conclusion In this paper, a global determination checklist is presented to map out the influence of different combinations of critical variables, during all pre-slaughter phases, on the pork quality and the risk for PSE meat, measured in the slaughterline. Despite the well-known difficulties to measure meat quality and large variability in observed pHLT, this table gives a clear indication of the pHLT and the risk to develop PSE meat in the investigated process. Furthermore this study proves also that every stage during the pre-slaughter process has its impact on the quality of the produced pork and establishes that the closer to the stunning phase, the more critical the pre-slaughter handling of the pigs on the pHLT and PSE prevalence of the produced pork. The checklist is not only useful to predict the pork quality but also to advice intervention during the pre-slaughter process, in case during some pre-slaughter phases the handling of pigs is not according to the defined standards to deliver good pork meat. This study developed a very useful and upgradable tool for and by the pork industry, also again showing that the welfare of pigs might have a big impact on final meat quality, including perception by consumers. Further research will focus on the impact of loading aspects, such as sound levels during loading, loading time etc. on pHLT of pork and the PSE prevalence, finally to implement also the loading procedure at the farm in the classification table.
Acknowledgments This work was supported by Belpork vzw, Belgium. The authors would like to thank the staff of the participated slaughterhouses for their assistance.
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Van de Perre, V., Permentier, L., De Bie, S., Verbeke, G., & Geers, R. (2010). Effect of unloading, lairage, pig handling, stunning and season on pH of pork. Meat Science, 86, 931–937. Van der Wal, P.G., Engel, B., & Reimert, H.G. (1999). The effect of stress, applied immediately before stunning, on pork quality. Meat Science, 53, 101–106. Warriss, P.D., & Brown, S.N. (1994). A survey of mortality in slaughter pigs during transport and lairage. Veterinary Record, 134, 513–515.
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Meat Science journal homepage: www.elsevier.com/locate/meatsci
Pre-slaughter handling and pork quality L. Vermeulen a,⁎, V. Van de Perre a, L. Permentier a, S. De Bie b, G. Verbeke c, R. Geers a a b c
Laboratory for Quality Care in Animal Production, Catholic University Leuven, Bijzondere weg 12, B-3360 Lovenjoel, Belgium BELPORK VZW, Koning Albert II-laan 35, box 54, B-1030 Brussels, Belgium Biostatistical Centre, Catholic University Leuven, Kapucijnenvoer 35, B-3000 Leuven, Belgium
a r t i c l e
i n f o
Article history: Received 5 May 2014 Received in revised form 28 July 2014 Accepted 18 September 2014 Available online 16 October 2014 Keywords: Pre-slaughter stress pH Pork quality Pig
a b s t r a c t Environmental variables, as sound levels, were collected during the pre-slaughter process in 18 different Belgian commercial slaughterhouses. Four pre-slaughter phases were determined: firstly after arrival of the truck at the slaughterhouse and just before unloading, secondly during unloading, thirdly at lairage and finally while moving to the stunner. A total of 8508 pigs was examined during the pre-slaughter process, of which the pHLT (M. longissimus thoracis), at 30 min post-mortem was measured. For each pre-slaughter phase, variables which might influence pork quality were determined. Moreover, this study made it possible to infer a checklist to represent and predict PSE traits of pork for all kind of pre-slaughter situations. The checklist shows also that the impact on pork quality is more decisive for the variables measured close to the stunning phase. Hence, this information is useful for the industry to optimize handling of pigs, reducing the risk for PSE traits. © 2014 Elsevier Ltd. All rights reserved.
1. Introduction Pork production is a still growing industry on the international market (AHDB, 2014), but subjected to great pressure, due to an enhanced competition between export countries. Moreover, consumers still attach a great importance to the trade-off between price and quality but also to the way food is produced, taking into account durability aspects, such as animal welfare (Payne, Mullan, Trezona, & Frey, 1999; USDA-FAS, 2014). Therefore, all stakeholders aim for an optimal qualitative pork production, but too many meat defects still occur, especially Pale Soft and Exudative meat (PSE meat) (Adzitey & Nurul, 2011; Van de Perre, Ceustermans, Leyten, & Geers, 2010; Van de Perre, Permentier, De Bie, Verbeke, & Geers, 2010). PSE meat is caused by acute stress just before slaughter. Pigs genetically sensitive to stress (Halothane gene), but also normal pigs are prone to the defect (Kerth, 2013, chap. 7). Stress results in an accelerated rate of glycolysis. Early post mortem, this metabolism is anaerobic and thus produces lactic acid. A lower pH, due to the lactic acid, while the carcass temperature is still high, results in an increased protein denaturation within the meat (Bendall & Swatland, 1988; Breteler, Wes, Huiskes, Kanis, & Walstra, 1995; Garrido, Pedauyk, Bacon, Lopez, & Laencina, 1995). Due to this process, PSE meat has the property to have a high lightscattering capacity and a low water holding capacity (WHC) (Adzitey & Nurul, 2011; Offer, 1991; Offer & Knight, 1988). Scheffler, Park,
⁎ Corresponding author. Tel.: +32 494281222; fax: +32 16 321994. E-mail address: [email protected] (L. Vermeulen).
http://dx.doi.org/10.1016/j.meatsci.2014.09.148 0309-1740/© 2014 Elsevier Ltd. All rights reserved.
and Gerrard (2011) reported another explanation for the increased pH decline, instead of lactic acid production, namely the free protons and heat, originating from the ATP hydrolysis. To detect PSE meat, the pH of the meat has to be measured 30 min after slaughter. As Josell, Martinsson, Bogaard, Andersen, and Tornberg (2000) defined, the pH value 30 min after slaughter has to be below 6.1. But Van de Perre, Ceustermans, et al. (2010), Van de Perre, Permentier, et al. (2010) and Adzitey and Nurul (2011) reported that in countries where the incidence of PSE meat is high, a stricter pH value (≤ 5.9) can be used. Thereby, handling at the farm, genetics, the season and preslaughter handling, namely during transport, unloading at the slaughterhouse and the handling of the pigs in the slaughterhouse, are very important aspects that influence the stress level of the animal and thus are responsible for the development of aberrant meat quality (Brown, Knowles, Wilkins, Chadd, & Warriss, 2005; Van de Perre, Ceustermans, et al., 2010; Van de Perre, Permentier, et al., 2010). Van de Perre, Ceustermans, et al. (2010) and Van de Perre, Permentier, et al. (2010) listed, described and investigated the combined effect of those parameters. As a follow-up, the significant aspects for the pork quality were selected for each pre-slaughter phase, after which the conditions to comply with good pork quality, were formulated for each pre-slaughter phase. The objective is to build a combination table or checklist for different cases over all pre-slaughter phases which might cause a risk for the pH of the pork and the percentage PSE meat. This table could be very useful for slaughterhouses to evaluate their handling procedures, and if needed to intervene during the preslaughter process to optimize the pork quality.
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2. Material and methods 2.1. Experimental design In total, 8508 pigs were observed during the pre-slaughter phases, from March 2009 to March 2011 in 18 different slaughterhouses during 2 to 6 visits in each slaughterhouse. The pigs were heterozygous for the halothane or ryanodine receptor gene (Piétrain boar × homozygous negative sow). During each visit, it was attempted to survey two batches of pigs originating from two different farms, which were transported to the slaughterhouse by two different trucks. Pigs of one batch originated from the same farmer and thus had the same unique identification number. In general, pigs in one truck originated from one farm, due to sanitary measures. In total 181 groups of pigs were observed. Nevertheless, if there were pigs from a different batch on one truck, only pigs from one farm were observed. 2.2. Data collection 2.2.1. Pre-slaughter measurements During different phases in the slaughtering process, several influential factors of the pre-slaughter environment were recorded, from transport of the pigs to the moment of slaughtering (Tables 2 and 3). The mean sound level (Testo 815, Testo NV, Ternat, Belgium) (dB(A)) was recorded just before unloading, when the truck arrived at the slaughterhouse, and during unloading. This measurements took place near the truck at the unloading ramp during the whole unloading procedure. The transport time (min), the time elapsing from arrival at the slaughterhouse till start of unloading (min), the mean live weight of the pigs (kg), the total number of panting pigs on the truck, the unique identification number and the stocking density (m2/100 kg) were determined. Furthermore, the duration of unloading, the percentage vocalizing, falling and slipping pigs (%), pigs, having the tendency to turn back during unloading (%) and dead pigs (%) were counted. Unloading aspects, such as the use of a hydraulic lift (yes/no) and the angle of the ramp (°) were recorded. In the pens the number of pigs and the stocking density (m2/100 kg) were quantified, also the presence of drinking nipples (yes/no), of sufficient air flow (yes/no) and of an operational showering system (yes/no) was noted. Also the water temperature of the shower (°C) and the lairage time (min) were registered. During lairage, movement to the stunner and at the stunner, the mean sound level (dB(A)) was recorded, each time at the same place, during 10 min and as close as possible to the group of pigs. The number of slipping or falling pigs (%) during movement to the stunner was counted. Thereby the use of an electrical prod (yes/no) was noted. Finally the stunning method (gas, manual electrical, head-only, head-to-chest), the properties of the used method (CO2 concentration (%) or the voltage (V)) and the stunning efficiency (%), controlled by means of the corneal reflex test, were recorded (Tables 2 and 3) (Van de Perre, Ceustermans, et al., 2010; Van de Perre, Permentier, et al., 2010). 2.2.2. pH measurements The pH (Hanna HI99163, Hanna Instruments, Temse, Belgium) of the M. Longissimus thoracis (pHLT) was measured between the second last and the last rib, 30 min after slaughtering by using a pH electrode of glass (FC232D, Hanna Instruments) enclosed with an unbreakable stainless steel knife, to facilitate the measurements in a muscle. The apparatus was equipped with a built-in temperature sensor to compensate the pH for a change of temperature. At the start of the measurements and after every 20 measurements the pH electrode was treated with a cleaning solution for oils (HI 7077, Hanna Instruments, Temse, Belgium) and a cleaning solution for proteins (HI7073L, Hanna Instruments, Temse, Belgium). Further, the pH electrode was calibrated by using the standard solutions of pH 7 and pH 4. If the pHLT had a deviation of more than 0.01 units, the electrode was recalibrated.
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Due the high speed of the slaughter process, it was not possible to use the referential method of measuring pHLT 45 min after sticking. Therefore the same method for accurate pHLT measurements, recommended by Josell et al. (2000), Van de Perre, Ceustermans, et al. (2010), and Van de Perre, Permentier, et al. (2010) was used, as described in the introduction. pHLT was measured 30 min after sticking. To make the measurements repeatable, the site along the slaughter line, which corresponds to 30 min after sticking, was determined for each slaughterhouse. Those measurements were performed by the same person, using the same type of pH electrode. PSE meat was defined when the pHLT of the pork was less than 6.0, 30 min after sticking. Due to the fact that measurements took place on pigs heterozygous for the halothane gene, a risk to develop PSE meat was higher, as described in the introduction (Brown et al., 2005; Josell et al., 2000; Van de Perre, Ceustermans, et al., 2010; Van de Perre, Permentier, et al., 2010). 2.3. Statistical analysis Statistical model building was conducted with SAS 9.3 software (SAS version 9.3, SAS Inst., Inc., USA). First, the data was checked for normality and univariate analysis was performed (means and standard deviations). The whole pre-slaughter process was split into 4 stages, namely the transport phase, the unloading phase, the lairage phase and the phase at the stunner. Next, the effect of every observed variable (Tables 2 and 3) on the pHLT and the PSE prevalence was examined separately by using a mixed model, whereby slaughterhouse and sampled group of pigs (batch), nested within slaughterhouse, were used as random factors. Only variables classified as significantly (p b 0.05) influencing the pHLT and the PSE prevalence were considered in the model. Correlations between variables were calculated to check for multicolinearity problems. If significant correlations were found between covariates (|r| N 0.6), the most adequate and representative variable was kept in the model. Insignificant variables and variables with less than 80% of the measurements were left out of the model used to build the checklist or combination table. Finally, for every significant variable, criteria were defined to classify from which value the significant variable has a positive or negative effect on the pHLT. If every criteria, for each phase, was performed to ensure a pHLT value, which is considered as indicating no risk for PSE (pHLT ≥ 6), the phase was qualified as ‘Ok’; if not the phase was qualified as ‘Not Ok’ (pHLT b 6). To conclude all this information was merged in one table, whereby combinations of different situations were put together and the remaining pHLT and the potential risks to develop PSE meat (%), for the specific situations, were calculated. 3. Results and discussion In total 181 batches of pigs, containing 8508 pigs, were observed from arrival at the slaughterhouse until stunning, and pHLT was measured. This means an average number of 47 carcasses, randomly selected out of one batch, were examined. Table 1 presents the number of pigs and the number of batches, of which pre-slaughter parameters were observed and post-mortem pHLT was measured per visit, season and slaughterhouse with their respective stunning methods. The frequency distribution of pHLT is shown in Fig. 1, with a minimum pHLT of 5.33, a mean pHLT of 6.19 and a maximum pHLT of 6.95. At European level a prevalence of 8% PSE meat is reported (Kyriazakis & Whittemore, 2006, chap. 2), while this study shows a mean value of 15.10% of the measured carcasses with a high risk for PSE meat, based on pHLT. This difference might be explained by the genotype of the pigs, i.e. 100% heterozygous for the ryanodine receptor gene, being more prone to develop PSE traits (De Smet et al., 1996). Table 2 shows the number of observed pigs and the mean level (±SD) for all observed continuous pre-slaughter variables, subdivided for each pre-slaughter
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Table 1 Number of pigs and number of batches, of which pre-slaughter parameters were observed and post-mortem pHLTe was measured per visit, season and slaughterhouse (plant) with their respectively stunning methods. Number of batchesf
Number of pHLT measurements
Plant 1 Plant 2 Plant 3 Plant 4 Plant 5 Plant 6 Plant 7 Plant 8 Plant 9 Plant 10 Plant 11 Plant 12 Plant 13 Plant 14 Plant 15 Plant 16 Plant 17 Plant 18 a b c d e f
Springa
Summerb
Autumnc
Winterd
Total
Springa
Summerb
Autumnc
Winterd
Totaal
162 61 163 82 173 222 160 100 0 200 181 102 186 100 190 172 0 102
200 200 100 221 100 0 0 63 0 0 0 0 0 100 0 0 150 79
100 201 200 153 201 191 250 200 107 262 300 301 195 150 301 300 0 0
100 50 100 0 100 0 100 90 0 87 100 100 100 200 100 100 200 0
562 512 563 456 574 413 510 453 107 549 581 503 481 550 591 572 350 181
4 2 4 3 4 6 4 2 0 4 4 2 2 3 4 4 0 4
4 4 2 5 2 0 0 2 0 0 0 0 0 3 0 0 3 2
2 4 4 5 4 5 6 4 2 6 6 6 4 4 6 7 0 0
2 1 2 0 2 0 3 2 0 2 3 2 2 4 2 2 4 0
12 11 12 13 12 11 13 10 2 12 13 10 8 14 12 13 7 6
Stunning method CO2 Electrical Electrical CO2 Electrical Electrical CO2 Electrical Electrical Electrical CO2 CO2 Electrical Electrical CO2 Electrical CO2 CO2
Spring: 21 March–20 June. Summer: 21 June–20 September. Autumn: 21 September–20 December. Winter: 21 December–20 March. pHLT: pH of the M. Longissimus thoracis. Batch: Pigs of one batch originating from the same farmer and thus have the same unique identification number.
phase. All class pre-slaughter variables are presented in Table 3 for each pre-slaughter phase with the number of observed pigs and the percent of observations per class. 3.1. Significant variables for each slaughter phase The different significant variables of the global analysis are explained by each phase of the slaughter process after which the checklist is discussed.
3.1.2. Unloading During unloading, both the percentage vocalizing pigs and the mean sound level just before unloading and during unloading had a significant
Percent
3.1.1. Transport A stocking density of 0.41 m2/kg to 0.51 m2/kg on the truck resulted in a significant higher pHLT in comparison with lower or higher stocking densities. As Van de Perre, Ceustermans, et al. (2010), Van de Perre,
Permentier, et al. (2010), Nanni Costa, Lo Fiego, Dall'Olio, Davoli, and Russo (1999) and Guise and Penny (1989) indicated, low stocking densities cause more injuries, because pigs can fall during inconsiderate handling and high stocking densities lead to more fights. Not optimal stocking densities can affect the welfare of the pigs and thus increase the risk for PSE meat. Furthermore, a significant lower risk to develop PSE meat is observed if there were no dead pigs at arrival. So the transport phase is qualified as ‘Ok’ if there are no dead pigs and if the loading density on the truck is between 0.41 m2/kg and 0.51 m2/kg (Tables 2 and 3).
pHLT Fig. 1. Frequency distribution of pHLT.
L. Vermeulen et al. / Meat Science 100 (2015) 118–123 Table 2 Observed continuous, pre-slaughter variables for each pre-slaughter phase, the number of observed pigs (Na), the mean and the standard deviation (SD). Phase
Variable
N
Transport
Before unloading: mean sound level (dB(A)) Transport time (min) Time elapsing arrival–unloading (min) Mean live weight pigs (kg) Panting pigs (%) Stocking density on the truck (m2/100 kg) Dead pigs after transport (%) Unloading Mean sound level (dB(A)) Duration unloading (min) Vocalizing (%) Falling and slipping pigs (%) Turning back (%) Angles of the ramp (°) Lairage Mean sound level (dB(A)) Water temperature of the shower (°C) Lairage time (min) Number pigs in pen Stunning Mean sound level (dB(A)) Falling and slipping pigs (%) If gas stunning: CO2 concentration (%) If electrical stunning: voltage(V)
a
8438
Mean ± SD 73.54 ± 6.22
3421 61.28 ± 46.49 8483 15.13 ± 18.25 8028 115.31 ± 6.17 8483 0.21 ± 0.60 8003 0.44 ± 0.04 4223 0.09 ± 0.29 8376 78.08 ± 3.86 8483 14.37 ± 6.62 8438 4.82 ± 4.06 8438 4.19 ± 5.53 8438 0.54 ± 1.08 8295 6.23 ± 4.39 7983 78.46 ± 4.03 3889 16.46 ± 3.66 8508 100.85 ± 64.16 7745 56.21 ± 40.60 7912 86.09 ± 5.24 8508 0.69 ± 3.27 4024 86.84 ± 5.09 4484 291.49 ± 106.51
N: Number of observed pigs.
3.1.3. Lairage The mean sound level during lairage influenced the risk for PSE meat significantly, and hence has to be lower than 85 dB(A). Also
Table 3 Observed class, pre-slaughter variables for each pre-slaughter phase, the number of observed pigs (Na) and the percent of observations per class. Na
Percent
Yes No
5352 3156
62.91 37.09
Yes No
6153 2355
72.32 27.68
Yes No
8433 75
99.12 0.88
Yes No
3389 4619
45.71 54.29
Yes No
6976 1532
81.99 18.01
Gas Electrical
4024 4484
47.30 52.70
Effective Not effective
5651 2857
66.42 33.58
Variable
Unloading Hydraulic lift (yes/no)
Lairage Drinking nipples (yes/no)
Sufficient air flow (yes/no)
Presence showering system (yes/no)
Stunning Electrical prod (yes/no)
Stunning method
Stunning efficiency: if more than 15% of the pigs are not showing signs of unconsciousness during the corneal reflex test the stunning is not being effective.
a
N: Number of observed pigs.
slaughtering during the winter or autumn makes lairage being classified as ‘Ok’. As Guàrdia et al. (2004), Van de Perre, Ceustermans, et al. (2010), and Van de Perre, Permentier, et al. (2010) stated, high environmental temperatures in summer and temperature fluctuations might result in stress, making it difficult for the pig to maintain deep body temperature, which might result in a poorer meat quality. 3.1.4. Stunning The mean sound levels prior to stunning, the use of an electrical prod (Yes or No) and the quality of the stunning influenced the meat pHLT significantly, as also proven by Van de Perre, Ceustermans, et al. (2010), Van de Perre, Permentier, et al. (2010). But the mean sound level during movement to the stunner was not significant for the PSE risk in this global checklist, due to the multicollinearity with the mean sound level prior to stunning. The stunning phase is classified as ‘Ok’, in case the mean sound level prior to stunning is lower than 85 dB(A), no electrical prod is used and the stunning is effective. In general, this study established that every stage during the preslaughtering process has its impact on the quality of the produced pork. Therefore an overview is set up to indicate whether pigs are having risk to develop PSE meat or not and during which stages of the pre-slaughtering process (3.2). 3.2. Global classification checklist
effect on %PSE. Vocalizing pigs produce high pitched sounds and will activate the pigs' defense mechanism, resulting in stress (Warriss & Brown, 1994). Unloading is classified as ‘Ok’ if the vocalizing percentage is lower than 5%, the sound level just before unloading and during unloading is lower than 85 dB(A).
Phase
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Table 4 shows the effect of different combinations of handling pigs during the four significant stages in the slaughtering process, namely transport, unloading, lairage and stunning phase. The explained variation of this checklist for pHLT is 19.2% and 13.6% for the %PSE meat. The low values does not indicate that X and Y are unrelated, since the model was found to be statistically significant by the F-test, but it can be explained by the number of variables used in this model and the large variability in the dataset (Neter, Kutner, Nachtsheim, & Wasserman, 1996). Thereby some pre-slaughter data of measured carcasses were incomplete, for example when there were no sound levels, measured during lairage due to a technical defect. Thus, those observations were not used in the checklist. A total of 83 batches, meeting the requirements described in each horizontal line, was left to examine the global checklist (3820 carcasses of which the pHLT is measured). Firstly, %PSE was mainly affected by pre-slaughter handling, occurring just before stunning, i.e. the last phase of the handling procedure (Table 4, a, b, c, d, e, f, g, h), resulting in a lower mean pHLT and a higher percentage of loins with PSE traits, compared when the last phase of the pre-slaughter process was performed in terms to deliver good meat quality (Table 4, i, j), as explained in Section 3.1.4 (Van der Wal, Engel, & Reimert, 1999). A good pHLT (6.21 ± 0.08) and a low %PSE (13.53 ± 10.49) were found when only the unloading phase is classified as Ok (Table 4, c). It can be due to the low number of measured batches; thus more observations are required to decide on significant conclusions. Thereby when pigs are stressed during almost the whole slaughtering phase and not, abrupt, at the latest stage of the slaughter process, pigs have less stress then pigs subjected to abrupt, tremendous stress factors, as Kittawornrat and Zimmerman (2010) indicated. This was also proven if both transport, unloading, lairage and stunning procedures were not performed according to the conditions described above (6.13 (± 0.16)) (Table 4, a), comparing with the results if transport and stunning phases were classified as Not Ok (Table 4, g). Stressful periods alternate with stress less periods; thus pigs were more abruptly exposed and created a higher risk to develop PSE meat. Table 4 (d and g) shows that a higher pHLT and a lower %PSE were reported when only lairage was classified as Ok (Table 4, d), compared when also the unloading phase was classified as Ok (Table 4, g). More observations are needed to clarify this result. Thus the global checklist shows the closer in time the preslaughtering phase to the stunning, the more critical the phase in
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Table 4 Mean pHLTk and percentage of PSE meat ± SD (Standard deviation) in different status of transport, unloading, lairage and the stunning itself.
a b c d e f g h i j
Nl
Transport ⁎
Unloading ⁎⁎
Lairage ⁎⁎⁎
Stunning ⁎⁎⁎⁎
pHLTk
%PSEm
9 5 2 3 14 8 6 23 7 4
Not Ok Ok Not Ok Not Ok Ok Ok Not Ok Ok Not Ok Ok
Not Ok Not Ok Ok Not Ok Ok Not Ok Ok Ok Ok Ok
Not Ok Not Ok Not Ok Ok Not Ok Ok Ok Ok Ok Ok
Not Ok Not Ok Not Ok Not Ok Not Ok Not Ok Not Ok Not Ok Ok Ok
6.13 (±0.16) 6.14 (±0.09) 6.21 (±0.08) 6.17 (±0,09) 6.19 (±0.11) 6.19 (±0.09) 6.13 (±0.07) 6.20 (±0.08) 6.27 (±0.08) 6.30 (±0.10)
22.45 (±22.15) 23.69 (±16.44) 13.53 (±10.49) 16.51 (±12.00) 16.70 (14.51) 12.04 (10.74) 24.34 (13.91) 12.60 (11.37) 6.83 (±7.27) 5.13 (±1.00)
a, b, c, d, e, f, g, h, i, j
: References to specific cases, as explained in the text. pHLT: pH of the M. Longissimus thoracis. N: Number of batches, meeting the requirements described in each horizontal line. Pigs of one batch originating from the same farmer and thus have the same unique identification number. m PSE: Pale soft and exudative meat. ⁎ Transport is Ok if there are no dead pigs after transport and the loading density on the truck is 0.41–0.51 m2/100 kg. Otherwise the transport is Not Ok. ⁎⁎ Unloading is Ok if the percentage of vocalizing pigs is less than 5%, mean sound level just before unloading and during unloading is less than 85 dB(A). Otherwise the unloading is Not Ok. ⁎⁎⁎ Lairage is Ok if the mean sound level during lairage is less than 85 dB(A) and the slaughtering took place during the winter or the autumn. Otherwise the lairage is Not Ok. ⁎⁎⁎⁎ Stunning is Ok if the mean sound level prior to stunning is less than 85 dB(A), the use of an electrical prod is not frequent and the stunning is accurate. Otherwise the stunning is Not Ok. k l
terms of developing PSE meat. Thereby, pigs that are not treated in terms of PSE prevalence, as described in Section 3.1, can possibly recover during lairage. This is also proven by the higher mean pHLT of 6.27 (± 0.08) when only transport is classified as Not Ok (Table 4, i). No observations were found when only lairage and stunning were Ok. The highest pHLT was recorded in case every phase was classified under ‘Ok. The better the pre-slaughter conditions, the better the pork quality can be. The resulting %PSE followed the same trend of the mean pHLT. Although 83 batches of pigs were used to perform this analysis, Table 4 shows that this is inconclusive for investigating the relationship of the pHLT over the not mentioned classification-combinations, such as when every phase classified as Not Ok except the transport phase. Therefore more measurements are needed.
4. Conclusion In this paper, a global determination checklist is presented to map out the influence of different combinations of critical variables, during all pre-slaughter phases, on the pork quality and the risk for PSE meat, measured in the slaughterline. Despite the well-known difficulties to measure meat quality and large variability in observed pHLT, this table gives a clear indication of the pHLT and the risk to develop PSE meat in the investigated process. Furthermore this study proves also that every stage during the pre-slaughter process has its impact on the quality of the produced pork and establishes that the closer to the stunning phase, the more critical the pre-slaughter handling of the pigs on the pHLT and PSE prevalence of the produced pork. The checklist is not only useful to predict the pork quality but also to advice intervention during the pre-slaughter process, in case during some pre-slaughter phases the handling of pigs is not according to the defined standards to deliver good pork meat. This study developed a very useful and upgradable tool for and by the pork industry, also again showing that the welfare of pigs might have a big impact on final meat quality, including perception by consumers. Further research will focus on the impact of loading aspects, such as sound levels during loading, loading time etc. on pHLT of pork and the PSE prevalence, finally to implement also the loading procedure at the farm in the classification table.
Acknowledgments This work was supported by Belpork vzw, Belgium. The authors would like to thank the staff of the participated slaughterhouses for their assistance.
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