ELSEVIER

Meat Science, Vol. 45, No. 2, 253.-262. 1997 c, 1997 Elsewer Saence Ltd

Printed in Great Britain. All rights reserved PII: s0309-1740(96)00048-4 0309-174oj97 $17.00+0.00

Influence of Lairage Environmental Conditions and Resting Time on Meat Quality in Pigs

C. Santos,‘* J. M. Almeida,” E. C. Matias,O M. J. Fraqueza,Q C. Roseiroa & L. Sardinah

Wnidade de Industrias Carneas, Departamento de Tecnologia das Industrias Alimentares IBQTA, INETI, Estrada do Paco do Lumiar, PT-1699, Lisboa Codex, Portugal

bCentro de Abate de Suinos do Oeste, Qta do Munhoz, Milharado, PT-2665, Malveira, Portugal

(Received 3 1 December 1995; revised version received 10 May 1996; accepted 18 May 1996)

ABSTRACT

This study investigated the influence of lairage environmental conditions and resting time on pig carcasses and meat qualify. The experimental material consisted of 1001 cross Pietrain-Duroc-Hampshirex Belgium-LR-LW pigs, held in lairage for either ~30 min (direct slaughter) or between 2-3 h under 12”C/90% relative humidity (RH). ZoOCjSO% or 90% RH and 3S’CcjSOX or 85% RH. Prior to arrival at the lairage plant they were trans- ported for about 4560 min and subjected to a fasting period of 36 h before loading. Unloading operation and the driving of pigs to the point of stunning were carried out accord- ing to the practices used in the plant (sticks and electrical goads were used). Batches of 20-30 mixed pigs were used in each trial, held at a stocking density of approximately 0.55 m2/pig f x 100 Kg live weight).

Lairage environmental conditions (LC), significantly affected almost all measurements, but not pHt, in Semi-membranosus (SM) and Longissimus dorsi (LD) muscles and the carcass damage score. The influence of resting time (RT) was basically exerted on pH,,, deep ham temperature and in pHt, of SM, the internal muscle reJlectance being mostly unaffected. There were also significant batch (B) effects in a large range of parameters. Factors greatly interacted their inJruence on carcass and meat quality, denoting LCxB, LCx RTx B and LCx RT the most sign$cant eflects. RTx B only showed two low significant interactions for rigor value andpHr. in SM, suggesting that, conversely to the lairage environmental conditions the influence of resting time is practically unaffected by the day of slaughter.

The increase of lairage temperature decreased the frequency of normal carcasses, followed by an expressive higher incidence of PSE status. The influence of lairage relative humidity on the PSEIDFD muscle incidence depended on the associated temperature, but the most important detrimental effects were noticed in experiments carried out at 35°C.

In respect to lairage resting time, the influence on meat quality is strictly related to environ- mental conditions, mainly the temperature. Nevertheless, and excepting the assays at 35”C/85% RH, direct slaughter of pigs ( = 30 min in pens) generally produced less carcasses of normal quality than resting periods up to 2-3 h. 0 1997 Elsevier Science Ltd. AN rights reserved

*To whom correspondence should be addressed. Tel.: + 351 17165141. Call: 2906. Fax: + 351 1 7163786. E-mail: uic@dtia.ineti.pt

253

254 C. Suntos et al.

INTRODUCTION

The ante-mortem handling of slaughter pigs has proved to be critical for the expression of genetic variations in meat quality, causing stress and physical pain, Among the stressors, adverse climatic conditions during transport and lairage can be important (Lambooy et al., 1987; Honkavaara, 1989; Schrama et al., 1994). According to these authors, higher environmental temperatures affect the animal’s ability to keep the body temperature con- stant, inducing higher post-mortem muscle temperature and poorer meat quality. Lendfers (1968) and Warriss (1991) also concluded that meat quality appeared significantly damaged, when pigs were subject to higher lairage temperatures. However, Scheper (1971) pointed out that the poorest meat quality was associated with cold seasons in Germany. However, the higher range temperatures of most known studies tested under commercial conditions are moderate when compared with those in Mediterranean slaughter plants during hot seasons. On the other hand, the environmental relative humidity, also assumed to be an important parameter by its influence on the evaporation level and subsequently on the animal’s upper critical temperature (Schrama et al., 1994), has been scarcely considered.

The present study was performed to assess, under controlled environmental conditions, the influence of lairage temperature and relative humidity on pork quality when pigs were held in pens for up to 30 min (direct slaughter) or between 2-3 h.

MATERIALS AND METHODS

Test animals

A total of 1001 cross Pietrain-Duroc-Hampshire x Belgium-LR-LW pigs, unmixed during transport from the farm to the slaughter house (45-60 min) and subjected to a fasting period of 36 h before loading, were used. Unloading and the driving of pigs to the point of stunning were carried out according to the practices used in the plant (sticks and electric goads were used). Batches of 20-30 mixed groups of pigs were used in each trial, held at a stocking density of approximately 0.55 m*/pig (w 100 kg live weight).

Facilities

The controlled environmental area housing the pigs was built in one lairage pen, measur- ing 2 m wide, 10 m long and 2.5 m high. The temperature of the air was controlled through a refrigeration system (evaporator Centauro, mod. CB 103/condenser Tuareg R22) for cooling and by electrical resistance for warming. The relative humidity was changed through a water spray device or by the refrigeration system itself, for increasing or decreasing the water vapour in the air. The ventilation was maintained by the ventilator of the refrigeration system (3.900 m3/h) and by a fan.

The relative humidity was recorded using cracked chromium oxide sensors and thermohygrometers and the temperature through type K thermocouples and thermistors.

Experimental conditions

Measured environmental conditions were 12”C/90% relative humidity (RH), 2O”C/80% or 90% RH and 35”C/50% or 85% RH, to simulate winter, mild summer and hot summer seasons in Portugal. The effect of 35”C/85% RH on meat quality was also assessed in this work, despite its occurring rarely in practice, in order to allow comparison of the results with an extremely stressful condition. The tested resting times were around 30 min and between 2 and 3 h (Table 1).

Lairage conditions in pork quality 255

Meat quality evaluation

After electrical stunning (420 V/2-3s) the half carcasses were ready for cooling in about 20 min. The chilling system included rapid cooling (4”C/34 ms-‘) for 1 h, followed by an overnight equilibration at 2”C/l-2 ms- i. For measurement purposes the carcasses were diverted from the slaughter line just before the entrance to the chilling tunnel. Approximately 30 min after slaughter, measurements were made of the pH1 in the M. semimembranosus (SM) and M. longissimus dorsi (LD) (Knick 655 pH-meter, electrode Ingold Lot 406M6-DXK 57/25), the rigor state in the SM (Rigormeter), the deep ham temperature (Fluke 52 thermometer, K-type thermocouple) and the skin damage score (Cpoint scale; 1, no damage; 4, severe damage). After measurements, the carcasses were returned to the line (* 1 h after slaughter), and followed the normal cooling procedure referred above. The meat quality evaluation at 24 h post mortem included pH, and FOP (Fibre Optic Probe; MacDougall, 1984) in M. biceps femoris (BF), SM, M. adductor (Ad), LD, and M. semispinalis cupitis (SC).

Muscles were classified as PSE, slightly PSE, DFD and slightly DFD according to Table 2.

In the Figs, 1 PSE, 2 PSE and 3 PSE or 1 DFD, 2 DFD and 3 DFD under the bars mean, respectively, carcasses having 1,2 or all muscles of the SM, BF, LD group classified as PSE or DFD.

Statistical methods

Statistical comparison of the three factors: lairage temperature, relative humidity and resting time was performed using the factorial mode-analysis of variance based on a completely randomised block experimental design (Bailey, 1981) to determine which fac- tors (temperature, relative humidity, resting time), and any interactions between factors, significantly affect the carcass and meat quality parameters. Levels of P < 0.05 were taken to be significant. Differences between individual means were tested using Duncan’s multiple range test (Sokal & Rohlf, 1981).

TABLE 1 Number of Tested Pigs under Different Lairage Environmental Conditions and Resting Times

Resting time

12”C/90% 2O”C/SO% 2OYJ90 % 35%/50% 3YCj85 %

30 min 137 59 90 60 60 2-3 h 73 172 148 86 116

TABLE 2 FOP and pH, Values Used for the Classification of Different Meat Quality Categories

PSE Slightly PSE DFD Slightly DFD

FOP

>60 50 < FOP160

pff,

26.1 5.9<pH, < 6.1

256 C. Suntos et al.

RESULTS

General

The overall means and variance ratios (F-values) for all evaluated parameters are depicted in Table 3.

Lairage conditions (LC), including temperature and associated relative humidity, affected significantly almost all measurements, but not the pH1, in SM and LD and the carcass damage score. There were also significant batch (B) effects in a large range of parameters, but conversely to lairage conditions, pHt in SM and LD and skin damage were now greatly influenced whereas the pH, of muscles was not affected at all. Compar- ing the interference of lairage conditions and batch in the internal reflectance values in different muscles, both factors influenced significantly the rest&s but the latter to a lesser extent. The influence of resting time is basically exerted on pH,, deep ham temperature and in pH, of SM, the internal muscle reflectance being mostly unaffected.

Factors also interacted greatly in their influence on carcass and meat quality para- meters, with LC x B, LC x RT x B and LC x RT showing the most significant effects. RT x B only showed two interactions of minor real importance for rigor value and pHt in SM (P < O.OS), suggesting that, conversely to the lairage conditions, the influence of resting time on the carcass and meat quality is practically unaffected by the day of slaughter.

All tested pigs survived the experimental conditions.

Lairage environmental conditions

Lairage environmental conditions significantly affected the carcass deep ham temperature and the rate of rigor mortis onset measured on SM (P<O.OOl), the pH, in BF, SM, AD, LD (PC 0.001) and SC (PC O.Ol), the internal muscle reflectance value (FOP) in general (P < O.OOl), but not the pHt or the skin damage score (Table 4).

TABLE 3 Overall Mean and F-Values for all Measurements

F-values (main eflects) F-values (interactions)

OveraN Lairage Resting Batch LCxRT LCxB RTxB LCxRTxB mean Conditions Time

(n = 1001)

T (“Cl 41.0 54.6*** 23.5*** 5.8*** 8.7*** Rigormeter 8.5 5 6*** 0.0 4 7*** 2.7* Skin damage 1.4 1:7 3.1 2:9** 1.5 PHI,SM 5.94 0.4 8 5*** PHILD 5.94 2.3 1:1

3.8*** 7.1*** 7 1*** 7.5***

pH,.BF 5.75 9 6*** 11:9***

28.9*** 0:8 2.1 pH,.SM 5.63 23.9*** 0.9 3.3** pH,Ad 5.84 6 2*** 22.7*** 1.2 0.9 PH,LD 5.55 13:6*** 32.0 1.8 2.5* PHX 6.14 4.2** 24.3*“* 1.5 2.3 FOP BF 56.9 11.9*** 6.4* 2.9** 4.2** FOP SM 52.9 10.7*** 3.1 2.5* 8.3*** FOP Ad 44.2 9.0*** 0.4 2.5* 6 8*** FOP LD 54.1 9.5*** 0.4 3.1** 4:6**

*, **, *** =significant at 5%, l%, 0.1% levels, respectively.

2.1* 0.1 0.9 3.4* 6.4*** 2.0

33*** 3.2* 0.9 2.8 2.9** 0.2 3.3*** 0.1 3.3*** 0.5 4.5*** 0.6 4.9*** 2.4 6.3*** 1.2 4.1*** 0.0 4.2*** 0.6 7.3*** 1.0

3.6** 2.0 4 6*** 3:4** 3.9** 4.9*** 7.3*** 3.5*** 6.4*** 4.2*** 4 3*** 0:9 2.4* 7,6*+*

Lairage conditions in pork quality 251

In relation to lairage temperature, pigs held at 35°C produced, compared to those penned at 12°C and 2o”C, carcasses with significantly higher deep ham temperature, irrespective of the low or high associated relative humidity. At that temperature (35°C) the increase in relative humidity from 50% to 85% also induced a significant elevation of muscle temperature, the opposite effect occurring during the assays carried out at 20°C. This discrepancy in trends could possibly be related to a large variation of halothane positive, negative or heterozygous pigs among the batches under this lairage temperature. In fact, a higher variation in meat quality occurred in experiments carried out at 2o”C/ 80%RH over 2-3 h, where the frequency of carcasses in which the incidence of LD with a FOP value > 50 ranged from 21% to 73% (data not given).

Regarding the effects on rigor onset, pigs in lairage at 20”C/90%RH and 35”C/50%RH showed lower values, being significantly different from other lairage environmental treatments.

The influence on pH, depended greatly on the muscle under consideration. However, and despite the lack of a clear trend among the different treatment groups, pigs held in lairage at 20”C/90%RH and at 35°C irrespective of the RH condition showed, in general, lower pH, mean values. Regarding the muscle internal reflectance (FOP), experiments carried out at 20”C/90%RH and 35°C for both humidity conditions tested gave rise, except for LD, to significantly higher values than the other lairage treatments. In this regard, the influence of temperature depended on the tested relative humidity and varied with the muscle under evaluation as well. In Ad muscle, FOP values appeared significantly greater at higher humidities at 20°C and 35”C, while this trend was only observed at 20°C for SM and BF. M. longissimus dorsi was not significantly affected by environmental humidity either at 20°C or 35°C.

The general consequences of lairage environmental conditions on the frequency of carcasses denoting PSE/Normal/DFD status on BF, SM and LD are shown in Fig. 1. The increase of lairage temperature clearly induced a detrimental effect on meat quality,

TABLE 4 Effect of Lairage Environmental Conditions on Carcass and Pork Quality

Lairage conditions (temperature/relative humidity) F-value

12”C/90%

n

T CC) Rigormeter Skin damage PHI .%I PHI LD PH, BF PH, SM PH, Ad PH, LD PH, SC FOP BF FOP SM FOP Ad FOP LD

210 40.gb 8.9’ 1.4 5.90 5.92 5.76’ 5.64’ 5.86’ 5.56b 6.12”

54.6“ 49.4” 40.6” 50.6”

2OqSOX

231 40.8’

8.8b 1.5 5.96 5.94 5.82d 5.61’ 5.89b 5.59’ 6.20b

53.0” 50.8O 41.2” 53.3”b

2o”C/90%

238 40.6*

7.ga 1.4 5.94 5.99 5.71” 5.58” 5.80” 5.54b 6.150b

58.9b 54.56 44.6b .53.4”b

35”C/SO% 3YCjSS %

146 176 41.2’ 41.4d

8.3” 8.7b 1.5 1.4 5.94 5.93 5.92 5.92 5.72”’ 5.75b’ 5.60” 5.63b 5.81” 5.80” 5.51” 5.54h 6.10” 6.09“

59.2h 60.2h 55.7h 55.7h 46.6h 50.1’ 56.1bc 58.6”

*, **, ***significant at 5%, l%, 0.1% levels, respectively. Means in the same row followed by different letters differ significantly (P < 0.05).

54.6*** 5.6*** 1.7 0.4 2.3 9.6***

1 I ,9*** 6.2***

13.6*** 4.2**

1 I .9*** 10.7*** 9.0*** 9.5***

258 C. Santos et al.

100% r 12°C / 90% rh 100%

r 20°C / 80% rh

100% r

20°C /90% rh

80% j-- 80% b 80% 1

60% 60% 60%

40% 40% 40%

20% 20% 20%

0% 0% 0% 3PSE I PSE I DFD 3DFD 3PSE I PSE I DFD 3DFD 3PSE 1 PSE 1 DFD 3DFD

2 PSE Normal 2 DFD 2 PSE Normal 2 DFD 2 PSE Normal 2 DFD

100%

80%

60%

35°C / 50% rh 100%

E

35°C / 85% rh

80%

60%

3PSE 1 PSE 1 DFD 3DFD 3 PSE 1 PSE 1 DFD 3 DFD 2 PSE Normal 2 DFD 2 PSE Normal 2 DFD

Fig. 1. Influence of lairage environmental conditions on the incidence of carcasses with different meat quality characteristics.

as shown by a smaller frequency of carcasses classified as normal. This decrease is followed by a higher incidence of the PSE status, particularly in the number of carcasses exhibiting this abnormal meat category, either concomitantly in the LD, SM and BF or just in two muscles of the group. It is also notable that the SM and LD were, in general, more affected by the lairage temperature than the BF (data not given). While the frequency of the PSE status in the BF was similar for pigs held at 12°C and 20°C and 9% higher at 35°C the incidence of this meat category in SM and LD was respectively 9% and 7% higher at 20°C than at 12°C increasing to 13% and 16% at 35°C. The higher incidence of carcasses affected by the DFD status from pigs held at 2O”C/80% RH is difficult to explain and might be related to any change on pig’s handling on the farm (perhaps, the fasting period). The influence of lairage relative humidity in the frequency of carcasses showing PSE/DFD muscle status depended on the associated temperature. The most important detrimental effects were however observed in the experiments carried out at 35°C where 7% less normal carcasses appeared at higher relative humidities by the reflection of both PSE and DFD meat frequency, respectively more 4% and 3%. In terms of PSE status it also must be pointed out that the number of carcasses seriously affected (LD, ’ BF and SM muscles, showing concomitantly this quality status) is 5% higher at 85% than at 50% RH.

Lairage resting time

Table 5 shows the influence of resting time on carcass and meat quality measurements. In this context, the increase in resting time from approximately 30 min to 2-3 h gave rise to carcasses with significant lower deep ham temperature (P<O.OOl) higher pHi, in SM (PC O.Ol), higher pH, in all measured muscles (PC 0.001) and lower internal reflectance

Lairage conditions in pork quality 259

TABLE5 Effect of resting time on carcass and pork quality

Resting time F-value

30 min 2-3 hours

n 406 595

T (“C) 41.1 40.9 Rigormeter 8.4 8.5 Skin damage 1.4 1.4

PHI SM 5.91 5.95

PHI LD 5.93 5.95

PH, BF 5.71 5.79

PH, SM 5.59 5.65

PH, Ad 5.79 5.86

PH, LD 5.52 5.51

PH, SC 6.08 6.18 FOP BF 59.2 55.4 FOP SM 52.4 53.3 FOP Ad 44.1 44.3 FOP LD 54.5 53.1

23.5** 0.0 3.1 8.5* 1.1

28.9** 23.9** 22.7** 32.0** 24.3**

6.4 3.1 0.4 0.4

*, ** = significant at 5% and 1% levels, respectively.

Means in the same row followed by different letters differ significantly (P < 0.05).

in BF (P < 0.05). Although not significantly different, FOP mean values in LD were also slightly lower for pigs slaughtered after 2-3 h in lairage. In respect to the incidence of muscle PSE/DFD in the carcass, the influence of resting time depended on the environ- mental conditions, mainly the temperature (Fig. 2). Nevertheless, the relative humidity is also a parameter to consider in experiments carried out at 35°C. In respect to the PSE status, pigs held in pens around 30 min under mild temperatures (12°C and 20°C) or at 35°C with low relative humidity, gave rise overall to poorer meat quality when compared with lairage times up to 2-3 h. However it must be emphasised that under the latter environmental condition and despite the higher frequency of normal carcasses in experi- ments carried out during 2-3 h (45% vs. 38%) the incidence of those seriously affected by that abnormal meat category is greatly enhanced (20% vs. 5%). Conversely, increasing the resting time from 30 min up to 2-3 h under 35°C with higher relative humidity was undoubtedly a detrimental effect. This was shown by a more than 15% increase in the PSE incidence, due basically to an increase in the frequency of carcasses where the LD, SM and BF presented concomitantly or just in two of them that quality condition (respectively + 9% and + 6%). Irrespective of the environmental conditions tested, a slight increasing in the DFD status was observed from pigs slaughtered after 2-3 h in lairage.

DISCUSSION

The different ante-mortem treatments were designed to produce a range of commercially feasible lairage, environmental and resting time conditions, in order to evaluate whether there were interactions among them in determining carcass damage and meat quality. In fact, such interactions exist, being of particular importance for the results. The variation in meat quality from batches held in lairage under the same environmental conditions and resting times, was probably due to a different incidence of genotypes in populations

260 C. Suntos et al.

100%

F 12°C /90% rh - 30 min. 100%

F

12”C/90%rh-2-3h

80% 80%

60%

2 PSE Normal 2 DFD

20°C /80% rh - 30 min. 20°C / 80% rh - 2-3 h.

80%

t

80%

t 60% 60%

40% 40%

20% 20%

0% 3 PSE I PSE I DFD 3

0% 2 PSE DFD NOIIWII 3 PSE

2 DFD I PSE I DFD

2 3 DFD

PSE Normal 2 DFD 100%

80%

60%

20°C /90% rh - 30 min. 100%

80%

60%

20°C / 90% rh - 2-3 h.

0% 3 PSE I PSE I DFD

0%

2 PSE 3 DFD

Normal 3 PSE

2 DFD I PSE I DFD

2 PSE 3 DFD

Normal 100%

2 DFD

r 35°C / 50% rh - 30 min. 100% r 35°C 150% rh - 2-3 h.

80%

c

80%

60% 60% t

0% 3 PSE I PSE I DFD

0%

2 PSE 3 DFD

Normal 3 PSE

2 DFD I PSE I DFD

2 PSE 3 DFD

Normal 2 DFD 100% r 35T / 85% rh - 30 min. 100% r 35T / 85% rh - 2-3 h.

60% 60%

40% 40%

20% 20%

0% 3 PSE I PSE I DFD 3

0%

2 PSE DFD 3

Normal PSE

2 DFD I PSE I DFD 3 DFD

2 PSE Normal 2 DFD

Fig. 2. Influence of iairage environmental conditions and resting time on the incidence of carcasses with different meat quality characteristics.

Lairage conditions in pork quality 261

tested, and reflecting the distinct responses of pigs to these factors. As has been stated before (Barton-Gade & Baltzer, 1991) halothane positive animals are quite insensitive to variations in pre-slaughter conditions, developing PSE and DFD meat regardless.

When exposed to warm environments, stress-susceptible pigs show accelerated heart and respiratory rates (Forrest et al., 1968), developing hypoxia and further metabolic alkalosis/acidosis if also subjected to physical stress (Judge et al., 1972); promoting higher body temperature and lower blood pH. In our study, in fact, carcasses from pigs held at 35°C showed higher deep ham temperature and muscle internal reflectance values than those penned at 12 or 20°C; but, conversely to what would be expected from the statement of Forrest et al. (1968) and the results of Honkavaara (1989) no significant relationship was found between LD or SM pHi and lairage temperature. In terms of the incidence of different meat quality categories, the consequences were a decrease in normal carcasses from 55% at 12°C to 48% at 20°C and down to 35% at 35°C. for experiments carried out at similar humidities (90”/0), reflecting basically an increase of the PSE status (respectively 38%, 47% and 58%). The frequency of carcasses with DFD meat was practically unaffected by lairage temperature. Nevertheless, the observed trend seems to be of real commercial concern, considering the short duration of the assayed resting times.

Because pigs dissipate body heat mainly through sweating and panting, higher humidity would be expected to further increase stress, affecting the upper critical temperature (Schrama et al., 1994) and causing discomfort. Randall (1983) also pointed out a detri- mental influence of environmental relative humidity on the well being of fattening pigs, but he reported in addition that pigs were mostly insensitive to humidity below environ- mental temperatures of 30°C. In agreement with this author, the influence of relative humidity was mainly observed at 35°C. Comparing the results at 50% and 85% RH, the latter condition gave rise to 7% less normal carcasses. Despite the similar frequency of carcasses with PSE meat (54% vs 58%) the experiments carried out at 35”C/85% RH produced 5% more of those affected by this abnormal meat category. Due to the fortuitous incidence of such environmental conditions in Portuguese lairage plants (high temperature and high humidity) and also to the short time elapsed under it (Santos, 1993) it might be concluded that pigs are mostly unaffected by humidity.

However, as stated before by Honkavaara (1989) the effect of lairage environmental conditions on the incidence of carcasses deviating from normal (PSE/DFD status) cannot be dissociated from the resting time pigs spend in pens, the consequences being completely different if pigs were held for 2 30 min or 2-3 h.

The influence of environmental conditions on meat quality in the experiments carried out over 30 min is less relevant than when pigs were penned for up to 2-3 h. An interest- ing observation was that pattern of meat quality from pigs held in lairage approximately 30 min at 35°C irrespective of the relative humidity, did not much differ from, for example, those experiments carried out at 20°C and could even be considered less affected generally. In fact, it was noticed (Fraqueza et al., 1997) that pigs adopted a resting attitude earlier when penned at 35°C such behaviour corresponding perhaps to a physical response to the uncomfortable ambient. Approximately 50% of the population was already lying down (not huddling) by the end of the experiments at 35°C whereas at 20°C pigs maintained their initial exploratory attitude and their excitement rate was almost unchanged. This difference could suggest a better recovery from the stress associated with transport and unloading at 35°C and may possibly explain the similar incidence of meat quality, compared to experiments at 20°C.

Except for the assays at 35”C/85% RH, direct slaughter of pigs generally produced less carcasses with normal quality than resting periods up to 2-3 h. Nevertheless, it must be emphasised that in experiments at 35”C/50% RH during 2-3 h, the lower incidence of carcasses with PSE meat (48% vs 62%) is nevertheless characterised by a higher frequency

262 C. Suntos et al.

of those seriously affected (20% vs 5%). According to these results, stress-susceptible pigs, held in lairage at moderate temperatures, should rest in pens for at least 2-3 h to recover from transport and unloading stress; in contrast, under warmer conditions, they should be slaughtered as quickly as possible in order to minimise the added temperature stress.

ACKNOWLEDGEMENT

The authors wish to express gratitude to Dr P. Warriss for his interest, help and advice.

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40th Znt. Congr. Meat Sci. Technol., Hague. Sokal, R. R. & Rohlf, F. J. (1981). Biometry, 2nd edn. W. H. Freeman & Company, New York. Warriss, P. D. (1991). Proc. 37fh Znt. Congr. Meat Sci. Technol., Kulmbach, p. 301.