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ARTICLE ORIGINAL
Incidence of pre-slaughter stress on meat
quality of non sensible pigs
° M. FRANCK*, ° PH. FIGWER, °°° A. JOSSEL, ° MT. POIREL, A. KHAZZAKA and ° X. PASTEUR
° ENV de Lyon, Laboratoire de Zootechnie, F-69280 Marcy L’Etoile
* Corresponding author. Tel.: +33-478872665; fax : +33-478872667; e-mail address: [email protected]
SUMMARY
RÉSUMÉ
Pigs (n=186) of the same genetic strain at the RN and HAL loci, i.e.
rn+rn+ / NN, were slaughtered in two abattoirs (referred to as A1 et A2). All
pigs were anaesthetised with CO2, using a mixture of air (30 %) and CO2
(70 %). One hundred and twenty-eight pigs were slaughtered in A1 (corusinga restrainer) and fifty-eight pigs were slaughtered in A2 (backloading)
at a rate of 720 pigs per hour per slaughterline. In A1, the pigs were led in
a single file to the restrainer which introduced them individually into the
stunning machine. In A2, the pigs walked 5 or 6 abreast towards the stunning machine, being pushed by a sliding door from the piggery to the cradle of the machine without human intervention.
The pH was measured at 40 min, 2h30 and 24h after slaughter in the
semimembranosus muscle (SM). Colorimetric values (L*, a* and b*) were
measured after deboning on the internal surface of the SM. The hams were
graded as follows: 1, no PSE zone; 2, doubtful; 3, PSE zones in the SM and
sometimes in the internal flexor muscle; 4, PSE zones in all the flexor
muscles; each one of these grades being squared with pre-thresholded gaps
of luminance.
The muscle pH value was higher in A2 than in A1 at pH1 (40min). L*
and a* value (P < 0.001) were higher in A1 than in A2. There was a remarkable difference between the two abattoirs in the proportion of hams graded
3-4, with 17,7% in A1,vs. 5 % in A2.
Waiting-time before slaughter affected the pH value at 24h. The values of
pH 1 and pH 2.5 decreased with the increase in the meat quality score in the
two abattoirs.
The result of the present study indicate that the method of handling the
pigs to the stunning device affects the frequency and importance of PSEzones in the ham. The stressless automated driving of groups of animals to
the stunning machine, combined with the backloading of a nacelle, (compared to a traditional system driving pigs in single file, using electrical
goads and a queue up restrainer) is beneficial with respect to both meat quality and animal welfare.
Influence du stress pré-abattage sur la qualité de la viande de porcs
génétiquement peu sensibles au stress. Par M. FRANCK, PH.
FIGWER, A. JOSSEL, MT. POIREL, A. KHAZZAKA et X.
PASTEUR.
KEY-WORDS : meat quality - PSE - pig - stress - slaughter.
MOTS-CLÉS : qualité de la viande - PSE - cochon - stress
- abattoir.
Revue Méd. Vét., 2003, 154, 3, 199-204
Cent quatre vingt six porc rn+rn+ / NN aux locus RN et HAL sont abattus dans deux abattoirs A1 et A2. Tous les porcs sont anesthésiés avec un
mélange air/CO2 (30 % / 70 %) ; 128 porcs sont abattus dans l’abattoir A1
équipé d’un restrainer classique avant le poste de narcose et 58 dans l’abattoir A2 équipé d’un poste de narcose avec chargement par l’arrière ; le rythme d’abattage est le même dans les deux abattoirs (720 porcs par heure).
Dans l’abattoir A1, les porcs sont poussés dans le restrainer par quatre opérateurs alors que dans A2 les porcs passent de la porcherie d’attente au poste
de narcose par une porte poussante et par lots de 5 à 6 porcs sans intervention humaine et donc sans stress.
Le pH est mesuré à 40 min., 2h30 et 24h après abattage dans le muscle
semi-membraneux (SM). Les valeurs colorimétriques (L*a*b*) sont mesurées après désossage sur la surface interne du SM. Les lésions de PSE sont
qualifiées comme suit : 1, absence de PSE ; 2, douteux ; 3, lésions de PSE
localisées sur le SM ; 4, extension des lésions de PSE sur l’ensemble des
muscles fléchisseurs.
Les valeurs du pH1 sont plus élevées dans l’abattoir A2 et les valeurs
L*a*b* sont plus élevées dans l’abattoir A1 ; les pourcentages de jambons
des classes 3 et 4 sont significativement différents (17,7 % dans A1 vs 5 %
dans A2). Le temps d’attente modifie les valeurs de pH 24h. Le pH 1 et le
pH 2,5 diminuent avec la détérioration de la qualité des jambons dans les
deux abattoirs.
Les résultats de cet essai montrent que le stress des porcs avant la narcose affecte la fréquence des lésions de PSI dans le jambon ; l’absence de
stress associé au chargement de la nacelle par lots de 5 à 6 porcs (comparé
au système traditionnel de conduite des porcs en file indienne dans un
restrainer par des opérateurs équipés de piques électriques) est bénéfique à
la fois au bien être de l’animal et à la qualité de viande.
200
Introduction
The stress can induce in the pig serious but localised
lesions of exudative myopathy. This myopathy induces PSEzones in the hams, called «unstructured meats» [4]. The sorting, the transport, the unloading of the pigs at the slaughterhouse, the lairage time and the passage through the restrainer
to the station of narcosis are many periods of stress, and one
can only measure with difficulty the incidence of each one on
the expression of this polyfactorielle affection. Moreover the
genetic types are also in question : the pigs carrying «n»
allele at the locus HAL [1, 4, 9, 11, 12] and/or RN- allele at
the locus RN [8,9] are very stress-suceptible, with important
variations in particular per series of slaughter, but all the
authors also recognize that the non carriers of these alleles
can present lesions [1, 4, 9]
The originality of this work is due to the choice of the individuals without alleles «n» (strongly inductor of PSE-zone)
to locus HAL and without RN- (strongly inductor of PSEzone) to locus RN. The objective was to quantify the impact
of the stress pre-narcosis in slaughter-houses (A1) where
stress is regarded as major and contrary with the rules of
well-being (traditional handling system -TS- for STOIER et
al) [13], contrary to the other (A2) where stress is quasi nonexistent. (low stress handling system -LSS- for STOIER et
al.) [13]. The aim of this article was (i) to confirm or invalidate the hypothesis that stress may affect the presence of
«PSE-zones» on «non stress suceptible pigs» (rn+/rn+); (ii)
to draw a parallel between this result and the former one
concerning a similar study on «stress suceptible pigs» (RN-).
Material and methods
A) ORIGIN AND CONTROL OF THE ANIMALS.
One hundred and eighty six homozygote pigs at the Rn
locus (+/+) and HAL locus (NN) were used. They were
issued from the same cooperative farm and the same parental
stock, fattened until a liveweight of 105 kg. At harvest, the
pigs were loaded on air-conditioned transport trucks by
groups using an elevator. At slaughterhouse, after an average
lairage-time of 2 hours (extremes 1h to 4h), pigs (which came
from different rearings and were in no circumstances mixed)
were slaughtered in two different ways: slaughterhouse A1
(reference, that is Traditional System) and slaughterhouse A2
(conceived to induce minimal stress, that is Low Stress
System). The two slaughter chains used in A1 and A2 only
differ from each other by the way of leading the pig to the
narcosis station. In A1 pigs go through the restrainer by a
queue up procedure contrary to A2 in which they are walking
4 or 5 abreast towards the stunning machine. In these two
cases, however, the used narcosis is CO2 gas, but when in A1
the nacelle is single, in A2 the place is as large as containing
4 to 5 pigs. The other stations of the two slaughters-line are
quite identical. One hundred and twenty eight pigs resulting
from 11 breedings constituting the first batch were slaughtered in A1, and 58 pigs coming from 5 breedings, constituting
the second batch were slaughtered in A2. In A1 abattoir, lairage-time is 1h40 versus A2 abattoir in which lairage time is
FRANCK (M.) AND COLLABORATORS
either 1h40 or 20h. Slaughter takes place on average 11 hours
after the last meal in the two slaughterhouses, narcosis being
carried out by a mixture of air (30 %) and CO2 (70 %) at the
rate of 720 porks per hour then distributed on the two parallel chains of treatment of the carcasses.
After evisceration, the carcasses were forwarded into the
room of fast refrigeration (-18°C for 30mn with air speed
10m/s in both abattoirs) then were stored at 2°C in similar
conditions before being carved up and deboned, on the day
following the slaughter. Colorimetry was carried out immediately after the deboning on the internal part of the SM in
accordance to the procedure described by FRANCK et al.[4],
that is close to the emergence of the arteriovenous beam of
the femoral one.
B) MEASUREMENTS
- Carcasses weight and lean meat percentage (Hennessy
Grading Probe) were registered on the slaughterline,
- The pH value was measured at 40 min (referred to as pH
1) with a Knick Portamess 911 pH-meter and a xerolyte glass
combination electrode, in the SM.
- The pH value at 2.5 h after death (referred to as pH 2.5)
was measured in room of cooling in the SM with the same
apparatus on only one of the two hams, 5cm approximately
above the pubic symphysis.
- The pH value at 24 h was measured just before the deboning process on the two hams.
- The measurement of colorimetric values (L*a*b*) of the
SM of the right hams was carried out 24 hours after stunning
and immediately after deboning, therefore on the internal
face of the muscle, with a Minolta CR 300 chromameter (diameter 8 mm, 0° viewing geometry, Osaka, Japan).
- The importance of PSE-zones of hams were scored according to BARBRY [4]: 1, no PSE-zone; 2, doubtful; 3, PSEzones in the SM and sometimes on the internal flexor
muscles; 4, PSE-zones in all the flexor muscles (sometimes
the whole ham is affected).
- Samples were taken from the SM and kept at -25°C for
further determination of the glycogen content (G) in order to
control the pigs as non-carriers of the RN- allele [3]. One
gram of meat was homogenised in 5 ml cold perchloric acid.
G Level was determined in the homogenate using the enzymatic method of DALRYMPLE & HAMM [2]. Animals
with a G content above 22 µmol/g were considered to be carriers and animals with a G content below 12µmol/g were
considered to be non carriers of the RN- allele. Pigs with a G
in SM between 12 and 22 µmol/g were DNA typed according
to MILAN et al. [10]
C) STATISTICAL ANALYSIS
Software MINITAB v.13.31 was used in order to check the
normality of samples. The unstructuration scores were submitted to a variance analysis taking into account the weak
distribution of this variable. The equality of the averages of
the breedings in each batch was tested by a chi2 test. The
comparisons were made by Anova with a controlled factor.
Revue Méd. Vét., 2003, 154, 3, 199-204
INCIDENCE OF PRE-SLAUGHTER STRESS ON MEAT QUALITY OF NON SENSIBLE PIGS
Results
201
B) RELATIONSHIPS AMONG MEAT QUALITY TRAITS
(TABLE II)
The comparisons carried out relate to the means values of
colorimetry and pH of the batches of hams in the two slaughterhouses.
A) DIFFERENCES BETWEEN ABATTOIRS (TABLE I)
The results of the measurements done in the two abattoirs
are presented in table I. Comparisons between A1 et A2 abattoirs are founded owing to the fact that the two batches of carcasses of pigs are very homogeneous in weight and lean meat
percentage.
Differences in pH between abattoirs were highly significant at 40 min (6.33 vs 6.65, that is 0,32 points; p < 0,001)
and 24h (5.49 vs 5.37) but not at 2.5 h. The a* value
(p < 0.01) differed between A1 and A2. There was a remarkable difference in meat quality scores, with 17.7 % of the
hams obtaining scores of 3 or 4 in A1, vs 5 % in A2
(p<0,001). It has to be noted that the value of the column
notation 3-4 for the slaughterhouse A2 relates to only 1 ham
out of 23.
The relations between allocated scores and the main parameters of meat quality, thoroughly studied by the inter abattoir analysis displayed score by score, assess that the fall in
the pH values are inversely proportional to the score, that is,
the higher the score, the lower the pH. This inter-abattoirs
analysis is based at the score 1 because of the strong strenght
and reports: (i). the differences are very significant
(p < 0,001) for pH1 as previously noted, and L*; significant
(p < 0,01) for pH 2.5 and a*, and non significant for pH 24 h
and b*.
Such results confirm that under some differences of
slaughtering method (A1 and A2) pH 1 and L* values could
be the most stress worthwhile values to term hams quality.
C) INFLUENCE OF LAIRAGE TIME BEFORE SLAUGHTER IN A2 ABATTOIRS (TABLE III)
Lairage time before slaughter had a significant influence
on pH 24h, L*, a* b* values, and also on meat quality scores
(p < 0.001)
Threshold of significance: *: p < 0,05; * *: p < 0,01; * * *:p < 0,001; NS: Nonsignificant
TABLE I. — Results of measurements of weight, TVM, pH, colorimetry, and structure scores.
Revue Méd. Vét., 2003, 154, 3, 199-204
202
FRANCK (M.) AND COLLABORATORS
Differences between scores in a same abattoir : the means in a same row bearing different letters are significantly different
at the probability level of 5 %.
Differences between abattoirs for a same score:*: P < 0.05; * *: P < 0.01; * * *:P < 0.001; Ns:Non significant
TABLE II. — Relations between structure score and meat quality.
Discussion
The protocol presents specific characteristics important to
underline: the two batches issued from the same co-operative
company were slaughtered in two different slaughterhouses
with, in both cases, a narcosis with CO2, the electric narcosis effect is thus not considered.
It is known that the mode of carcass chilling can affect the
development of PSE meat: in this study the difference in temperature between the two abattoirs was non significant. The
cold shock is more important in this test (-18°C vs -4°C)
compared to those of preceding works [4, 5, 6].
In the slaughterhouse A1 (TS), the stress is maximum
when the pigs enter into the restrainer (frequent use of the
battery, cries, scuffles). In the slaughterhouse A2 (LSS) the
corridors are of a sufficient width so that 4 to 5 pigs may
advance face, gently pushed by a sliding door towards the
nacelle of descent into the well with CO2; the entry from 4 to
6 pigs at the same time in the nacelle with CO2 is almost
voluntary; the noise is tiny room to its bare minimum, the
electrical goad is not used and the stress can be considered as
non-existent. As in our precedent study involving stress
suceptible pigs (rn+ / RN-) [6], the main difference between
the two abattoirs consisted in the way the pigs were led to the
stunning device, that is, in the level of resulting stress.
TABLE III. — Comparison of the meat quality between two batches issued
from the A2 abattoir with a different lairage time.
Revue Méd. Vét., 2003, 154, 3, 199-204
INCIDENCE OF PRE-SLAUGHTER STRESS ON MEAT QUALITY OF NON SENSIBLE PIGS
In this observation as in the preceding one [4,5], the pH
appears as a bad predictor of unstructured meats: (i) No ham
in A1 and A2 has pH 45 lower than the threshold of 5.8,
extreme limit given to identify the PSE at 45 minutes, (ii) at
pH 2.5 the mean values are not significant between the two
abattoirs, (iii) at 24h the pH values are significantly different
in outline and not in some details (pH 24h at score 1) even
when L* value is very relevant between abattoirs. As a matter of fact not only the difference in L* value at score 1 between A 1 and A 2 is very significant, but the values of L* per
level of notation are appreciably the same ones as those
observed before [4,5]. Such differences substantiate a stronger colorimetry of meat in the traditional slaughterhouse
(A1), raising that has been correlated to PSE zones [8].
Eventually, and unlike usual pattern in food industries that
use pH24 h as a predictive value of ham quality on the carving and deboning process, we propose that L* value could
be a more appropriate and accurate parameter than pH value
in labelling «PSE-zones» in deboned and carved hams.
Concerning «PSE-zones», it is generally assumed that
immediate preslaughter stress plays an important role in their
occurence in the pig hams. It was reported that the succession
of stress during 24h preceding narcosis was likely to cause
the «unstructured meats» (PSE zones) affection, more or less
worsened by a too short latency [6]. Of course the stress of
the sorting and transport is attenuated by the lairage - what
we confirm by a parallel study implying only the A2 abattoir
(table III), but its role is a minor one compared to that induced by the control at the station of anaesthesia. Actually, the
stress of the restrainer which lasts a few seconds just before
narcosis (10 seconds to 1mn according to the slaughter
rhythm, the length of the restrainer, the skill of the pig-keeper
and the number of blows of electrical goad) appears to be the
major cause in charge of the defects of destructuration. The
same observation was made by VAN DER WAL [14, 15] and
STOIER [13] with a clear variation of the pH and of the capacity of retention of water. In our study the comparison of two
batches of non sensible pigs (rn++), slaughtered under comparable conditions, that is a CO2 narcosis, shows that the
major effect of «PSE-zones» may be imputable to this stress
immediately preceding narcosis and induced by the control
of the animals into the passage of the restrainer. In our test the
suppression of this stress, initially under consideration for
reasons of animal wellbeing, decreases of almost 13 points
the frequency of unstructured hams since the defects of quality drop from 17.8 % in A1 to 5 % in A2.
In the present article, as in precedent one on pigs rn+ / RN[7], the stress effect is particularly significant on the fall of
pH in minutes following narcosis. Moreover the pH1 values
are identical for the two populations rn+/rn+ and rn+/RNrespectively in the slaughterhouses A1 (6,33 vs 6,32) and A2
(6,65 vs 6,56) [7] (Table IV: inter-comparison of the pH mean
values, the L* values and the percentage of structurless meat
in two genetic strains)
The results of the pH 2,5 in the two genetic strains
(rn+/RN- et rn+/rn+) are on the contrary more divergent and
significantly different in the slaughterhouses A1 (5,82 vs
5,95) and A2 (5,68 vs 6.03), just as the pH 24 h in A1 (5,39
vs 5,50). Such results are in conformity with current knowledge on acid meats and gene RN-, whose principal demonstration is a great amplitude of pH in the 24 hours following
narcosis and the bleeding [9]. The interest of the results of
table IV is to yield that this variation between the two populations (+ + and + -), at locus RN, is not related to the pH but
with the stress, and particularly that : (i) under stress conditions the most genetic «stress-suceptible population» of pigs
(rn+/RN-) reaches a percentage of PSE-zones higher than the
less suceptible one (rn+/rn+): 49.6 % versus 17.8 %; and (ii)
that under stressless conditions the most genetic ìstresssuceptible populationî of pigs (RN-/rn+) reaches a percentage of PSE zones higher than the less suceptible one
(rn+/rn+) : 16.4 % versus 5 %.
TABLE IV — Inter-comparison of the pH mean values, the L* values and the % of structurless meat
between genotypes, slaughterhouses and lairage time.
Revue Méd. Vét., 2003, 154, 3, 199-204
203
204
Conclusion
The results of the present study indicate that by leading
pigs to slaughter without antemortem stress the PSE-zone
drops from 18 % to 5 %. This way of leading pigs from the
waiting-area to the stunning device decreases significantly
the frequency of «PSE-zones» in hams. Results also indicate
that this defect can be targeted with L* value, a more reliable
parameter. Even if the L* value appears as the most reliable
indicator of the PSE-zones it will have to be validated to be
used by the industrial meat process. Likewise, the «PSEzones» problem in pigs will be reduced by the absence of
restrainers and the use of a backloading process coupled with
CO2 narcosis.
Acknowledgements
This research was funded following an agreement between Research and
Development of SQM and Zootechnia Laboratory of Veterinary School of
Lyon under the AQS (Alimentation, Qualité, Sécurité) program.
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