The effect of preslaughter lairage on serum thyroxine and cortisol levels at slaughter,and meat quality of boars,hogs and gilts

Commercial crossbred hogs and gilts, and purebred Landrace boars and gilts were slaughtered after a lairage period of either 2 or 24 h. The meat quality of the carcasses was assessed by measuring the pH of the Longissimus dorsi and adductor muscles at 45 min and 20 h post mortem. Serum cortisol and thyroid parameters were measured in blood taken at slaughter. The incidence of the pale, soft and exudative (PSE) condition was slightly higher in purebred Landrace pigs killed after a short lairage period than in those held in lairage overnight. The PSE condition tended to be more prevalent in Landrace gilts than boars. The percentage of carcasses classified as dark, firm and dry (DFD) was much greater in both commercial crossbred and purebred Landrace pigs killed after overnight lairage. The incidence of the DFD condition was greater in Landrace boars than gilts, particularly after overnight lairage. Serum cortisol levels were higher and serum total thyroxine (T₄) and free thyroxine indices (FTI) lower in pigs killed after a short lairage. Serum total T₄ and FTI values at slaughter were lower in boars than gilts.     

A survey of pre-slaughter conditions, halothane gene frequency, and carcass and meat quality in five Spanish pig commercial abattoirs

A total of 116 deliveries, comprising 15,695 commercial pigs delivered to five abattoirs, were surveyed during winter and summer. Information about on-farm fasting, transport duration and stocking density, and lairage time was collected. Cortisol, creatine phospho-kinase (CPK), and lactate, and DNA for halothane genotype were analysed in a subsample of pigs at exsanguination in every journey. Electrical conductivity (PQM) in semimembranosus muscle (SM) and carcass characteristics (Fat-o-Meater and skin damage) were measured in each carcass. pHu of SM was analysed in the laboratory in a subsample in every journey. Carcasses were identified as PSE or DFD based on PQM and pHu, respectively. The n gene frequency ranged among abattoirs from 54 to 8%. Mean lean content was 58.9% for nn, 57.3% for Nn, and 55.8% for NN pigs, though a difference of 2.5% lean was observed between two abattoirs with the same n gene frequency. A straight relationship of the incidence of serious PSE carcasses and n gene frequency was found. The overall incidence of serious PSE and DFD carcasses was 6.5 and 12.5%, respectively. A higher incidence of PSE carcasses was found in summer; in deliveries with <12 h on-farm fasting; with transport stocking densities >0.40 m(2)/100 kg pig; and in transports of <2 h duration. A higher incidence of DFD carcasses was found in winter; with transport stocking densities <0.40 m(2)/100 kg pig; transports of >2 h duration; and lairage times >9 h. Cortisol level in blood increased in winter and decreased after 12-18 h fasting time. A rise in the lactate concentration was observed in pigs transported in high stocking density (<0.40 m(2)/100 kg pig) and for a longer time (>2 h). All blood stress indices increase as increasing lairage time. Carcasses with more skin damage had higher levels of cortisol, CPK and lactate, and higher incidence of DFD meat, compared with non and low skin damage carcasses.     

Influence of lairage environmental conditions and resting time on meat quality in pigs

This study investigated the influence of lairage environmental conditions and resting time on pig carcasses and meat quality. The experimental material consisted of 1001 cross Pietrain-Duroc-Hampshire × 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), 20 °C/80% or 90% RH and 35 °C/50% or 85% RH. Prior to arrival at the lairage plant they were transported for about 45-60 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 according 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 m(2)/pig (≈100 Kg live weight). Lairage environmental conditions (LC), significantly affected almost all measurements, but not pH(1), 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(u), deep ham temperature and in pH(1), of SM, the internal muscle reflectance being mostly unaffected. There were also significant batch (B) effects in a large range of parameters. Factors greatly interacted their influence on carcass and meat quality, denoting LC × B, LC × RT × B and LC × RT the most significant effects. RT × B only showed two low significant interactions for rigor value and pH(1), 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 PSE/DFD 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 environmental 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.     

The effects of mixing,transport and duration of lairage on carcass characteristics in commercial bacon weight pigs

On arrival at the factory commercial crossbred pigs were subjected to various treatments: (i) penned in producer lots; (ii) mixed with pigs from another producer and (iii) mixed and subjected to an additional transport of 1-1.5h duration. Groups of pigs were killed on the day of arrival or after overnight lairage. Carcass parameters including pH₁ (pH 45 min post mortem) and pH_u (pH 20 h post mortem) values of the Longissimus dorsi (LD) and adductor muscles were taken post mortem. Mixing and transport had no statistically significant effect on any of the carcass parameters measured, although overnight lairage resulted in significant decreases in hot carcass weight, killing-out percentage and liver weight. The incidence of carcasses classified as pale soft and exudative [PSE (muscles with a pH₁ of 5.9 or less)] or dark firm dry [DFD (muscles with a pH_u of 6.2 or greater)] was high after both normal and overnight lairage. pH₁ and pH_u values of the LD and adductor muscles were not significantly affected by mixing or transport. Statistically significant differences in the incidence of DFD between treatment groups were observed. In general the incidence of DFD increased more after overnight lairage in pigs penned in producer lots, than in pigs penned in mixed producer lots.     

Incidence of different pork quality categories in a Portuguese slaughterhouse: A survey

This study was designed to evaluate the incidence of the PSE/DFD status in a Portuguese pig slaughterhouse, covering two seasons of the year (spring and summer) in order to find out if the proportions of those poor meat quality categories were sufficient to concern the meat industry. Meat quality classification was based on the measurements of the pH(60), pH(24), drip losses and colour (L, a, b) in the longissimus dorsi muscle (between the last third and fourth ribs) of 380 pigs randomly chosen from the line. The high global incidence of PSE and likely PSE (30%) as well as DFD (10%) carcasses and the enormous variation of the meat quality between the different days of analysis proves that the pig population presents a great variation of halothane genotype and that handling procedures have to be optimized in order to decrease stress and glycogen store depletion. The percentage of PSE carcasses during the summer season was double that found in the spring, probably due to a higher environmental temperature and relative humidity.     

The influence of exhaustion and electrical stimulation on the meat quality of young bulls: Part 2-Physical and sensory properties

The physical and sensory properties of meat from sixteen exhausted and sixteen gently treated young bulls were investigated. The influence of electrical stimulation was also studied. The meat was divided into three groups-meat with ultimate pH ≤ 5·80 (normal meat), 5·81-6·19 (medium meat) and ≥6·20 (DFD meat), respectively. DFD meat showed typical DFD properties and had a higher initial tenderness but a smaller increase in tenderness than normal meat during storage. The medium meat was tough and behaved in some ways as DFD meat and in others like normal meat. Lower correlation between shear force measurement and sensory evaluated tenderness was obtained for DFD than for normal meat. The cooking loss of DFD meat was about 10% lower than that of normal and medium meat. No significant correlation could be found between storage loss, cooking loss, frying loss and juiciness. The electrically stimulated meat was-especially for normal meat-more tender and juicy than unstimulated meat. No obvious influence due to electrical stimulation was noticed on colour, cooking loss, frying loss or storage loss. Electrical stimulation of stressed, but not exhausted, animals may produce meat with PSE properties.     

The influence of exhaustion and electrical stimulation on the meat quality of young bulls: Part 1-Post-mortem pH and temperature

After designing a method of handling cattle so that they reproducibly developed DFD meat, pH and temperature in cattle developing DFD and normal meat, respectively were studied. The influence of low voltage stimulation on both groups was also investigated. Depending on final pH and other characteristics of the meat, the carcasses could be assigned to subgroups representing pronounced DFD, slight DFD and normal meat, with and without electrical stimulation. In normal and in pronounced DFD carcasses electrical stimulation speeded up the pH drop but did not affect the final state of the meat. In stressed animals the pH values are variable for the first few hours post mortem. This effect is enhanced by electrical stimulation which, in carcasses with slight DFD (from stressed but not exhausted animals), may produce extremely fast pH drop and PSE-like meat. There is no evidence that electrical stimulation would influence the incidence of DFD in cattle slaughtered under commercial conditions. In normal animals electrical stimulation raised the carcass temperature during the first few hours post mortem by approximately 2°C. Carcasses from stressed animals had a higher temperature, independent of stimulation.     

A repeat national survey of muscle pH values in commercial pig carcasses

Measurements of pH values at 45 min post-slaughter (pH₁) in m. longissimus were taken in a total of 5598 commercial bacon weight carcasses. pH values at 24 h post-slaughter (pH₂) were taken on a further 5598 carcasses. The overall mean pH₁ was 6.39 with 15.1% of values less than 6.0. The overall mean pH₂ was 5.64, none of the values recorded were greater than 6.5. This survey shows a small increase over the 1983 study in the incidence of potentially Pale Soft and Exudative (PSE) carcasses. It found no evidence of a Dark, Firm and Dry (DFD) problem related to high ultimate pH.     

Risk factors influencing bruising and high muscle pH in Colombian cattle carcasses due to transport and pre-slaughter operations

The aim of this study was investigate risk factors as possible causes for bruising and high muscle pH under commercial operating conditions in Colombia. Data was recorded for 86 journeys referring to 1179 animals. Carcasses were analyzed in terms of muscle pH and bruises (site, size, severity and shape). Our results indicate that truck load density, stops during transportation of cattle and the lairage time at the plant increased the risk of bruises appearing on carcasses. A lairage time of 18 to 24 h at the plant increased the prevalence of bruises 2.1 times compared to lairage periods of between 12 and 18 h. Furthermore, intermittent stops during transit are a risk factor for the increase in the incidence of bruises. However, the transport time (up to 4 h) was not related to the presence of bruises and high muscle pH. Finally, steers were found to have less risk of presenting a high muscle pH.     

Risk assessment of DFD meat due to pre-slaughter conditions in pigs

A polychotomous logistic regression model was used to identify and assess the risk factors for pork becoming dark, firm and dry meat (DFD). A total of 116 deliveries, comprising 3075 commercial pigs delivered from different farms to five commercial Spanish pig abattoirs were surveyed. The DFD condition was described as an ordinal response variable (normal, moderate and serious) based on measurements of pH₂₄ in the Semimembranosus muscle. The abattoir, the floor of the lorry, the season, the gender, and the stocking density during transportation influenced the risk of DFD, as well as on-farm fasting time, lairage time and estimated carcass lean content. No effect of the RYR1 gene in the risk of DFD was found. Abattoirs should be especially careful with females slaughtered in winter, where the risk of serious DFD is 4.6% higher than with males slaughtered in summer. The risk of DFD increased with high stocking density and lairage time, and with on-farm fasting times longer than 22 h. Our results revealed that lowering the stocking density from 0.37 to 0.50 m² per 100 kg pig during transport would increase the risk of DFD pork by 11%.     

Physical and sensory attributes of hot-processed and conventionally chilled hams and bellies from electrically stimulated and non-stimulated pork carcasses

Forty-eight fresh hams and bellies were obtained from 24 market weight hogs (x = 94·5 kg) of which twelve were electrically stimulated (ES) by pulsing current immediately after exsanguination. The left side of each non-stimulated (NS) carcas was fabricated after conditioning for 3h post mortem at 17°C (NS hot-processed). The left sides of ES carcasses were fabricated 1 h pm. The right sides were fabricated following a 24 h cooler chill at 2°C (conventionally chilled: CP). Hams from ESCP carcasses had higher (P < 0·05) smokehouse yields than hams from NS carcasses. Hams that were hot-processed had higher smokehouse yields than the NSCP hams. Time of fabrication (1, 3 or 24h post mortem) did not affect smokehouse yields. Conventionally chilled bellies obtained from ES carcasses showed higher (P < 0·05) residual nitrite levels than those front electrically stimulated hot-processed (ESHP) carcasses. No differences were found for residual nitrite levels in the non-electrically stimulated sides. Panelists were unable to detect any sensory differences from the bacon strips. Sensory scores of ham slices were more juicy for non-stimulated hot-processed carcasses (NSHP) than those from ESHP carcasses. Panelists found the ham slices from NSCP carcasses to be more tender (P < 0·05) than those from electrically stimulated cold-processed (ESCP) carcasses. Results from this study clearly indicated that hot-processing of pork can provide hams and bellies that are acceptable for the production of cured hams and bacon of comparable quality and yield to those currently being produced under conventional processing methods.     

Differences in quality characteristics of normal, PSE and DFD pork

Differences in water-holding capacity, colour and tenderness/toughness were studied in 21 pork loins belonging to three quality categories, i.e. dark firm dry (DFD), normal and pale soft exudative (PSE). The division into the three groups was based upon the ultimate pH-values of the loins (< pH 5·5, pH 5·5-6·0, pH > 6·4). The PSE loins were characterized by a poor waterholding capacity, higher cooking loss and paler colour in contrast to the DFD category. The normal loins took an intermediate position. Neither sarcomere length, determined on fresh muscle tissue, nor Armour tenderometer values showed significant differences between the various quality categories. This was in contrast to the Warner-Bratzler (W-B) shear force values, determined on cooked loins, which had the lowest values in the DFD category. A strong relationship between the W-B values and the cooking losses was found. It was concluded that neither sarcomere length nor Armour tenderometer measurements were able to predict the shear force values of cooked pork loins.     

Functionality of high and low voltage electrically stimulated beef chilled under moderate and rapid chilling regimes

Chuck muscles from 24 beef carcasses electrically stimulated (ES) with either high or low voltage, or a combination of both, and submitted to conventional or rapid chilling regimes were used in a model system study (pH, salt-solubloe protein extraction, emulsifying capacity) and in frank-further fabrication and analysis (yield, color, texture). Glycolytic rates measured in the loin had no effects on the functional parameters or on the quality of frankfurters. The ultimate pH values of unstimulated carcasses remained higher than in any ES carcasses, and led to higher protein extraction (P ≤ 0·05). However, ES had no further influence on the emulsifying capacity or on frankfurter yield and quality parameters independently of the voltage used (P > 0·05). Chilling regimes had no influence on the functional parameters of the model system but slightly influenced the yield and chewiness of the frankfurters (P ≤ 0·05). Therefore, the use of any type of ES in combination with either conventional (Canadian) or more rapid chilling is unlikely to have commercial significance on the yield or quality of frankfurters.     

An estimate of the incidence of dark cutting beef in the United Kingdom

Eight slaughterplants with throughputs ranging from 20 to 300 animals per day were examined to estimate the incidence of dark cutting beef in the United Kingdom. Four thousand, eight hundred and sixteen animals were surveyed and information concerning animal category, source, season and preslaughter handling conditions recorded. Muscle samples were removed to estimate glycogen concentration and after incubation, ultimate pH. The overall incidence of dark cutting (pHu ≥ 6·0) was 4·1%. Increased incidence was associated with short (≤ 20 miles) and long (≥ 150 miles) transport distances. Slaughter on the day of arrival rather than overnight lairage also increased the incidence. Plants were classified into small (killing ≤ 50 animals per day) or large (killing ≥ 100 per day). Eighty per cent of the animals slaughtered passed through the large plants, and a higher incidence was also associated with these plants. Bulls had the highest incidence and heifers the lowest. A seasonal effect was recorded with the highest incidence found between July and October. The results, however, indicate that factors in addition to those examined are also important.     

A repeat national survey (ten years on) of muscle pH values in commercial bacon carcasses

Measurements of M. longissimus pH values at 45 min post mortem (pH(1)) were taken in a total of 5383 commercial bacon weight carcasses at fourteen bacon factories and meat plants in 1980/81. Comparable pH(2) values at 24 h post mortem were taken in a further 5150 carcasses. The overall mean pH(1) was 6·38 ± 0·29 (SD) with 12·8% of values less than 6·0. The overall mean pH(2) was 5·91 ± 0·18 with 0·6% of values greater than 6·5. Relationships between pH values and carcass weight, fat thickness and length were very low (maximum r = 0·05). Comparison of the results with a similar survey conducted in 1972/73 indicated that the proportion of carcasses with pH(1) values less than 6·0 has doubled (1972/73 result was 5·7%). The proportion of carcasses with high pH(2) values changed little.     

Presence of Salmonella in the red meat abattoir lairage after routine cleansing and disinfection and on carcasses

Foodborne pathogens, such as Salmonella, may remain in abattoir lairages after cleansing and pose a risk of transfer and contamination from one processing day to the next. These organisms may be transferred to the outer surface of animals held in lairage facilities, and the skin or hide may be a significant source of microbial contamination on the red meat carcasses subsequently produced. Sponge samples were taken from various sites in the lairage (n = 556), and single-pass sponge samples were taken from one side of red meat carcasses (n = 1,050) at five commercial abattoirs in Southwest England and tested for the presence of Salmonella. Of these, 6.5% of lairage samples were positive, containing estimated numbers of up to 10(4) Salmonella organisms per sampled area (50 by 50 cm). Salmonella was found on 9.6% of 240 lamb carcasses, 12.7% of 330 beef carcasses, 31% of 70 pig carcasses, 20% of 80 calf carcasses younger than 14 days of age, and none of 330 cull cow and bull carcasses. Subtyping divided the 137 isolates into seven serogroups and three pulsed-field gel electrophoresis clusters, and sensitivity testing against a bank of 16 antimicrobials indicated that 47 isolates had resistance to one or more antimicrobial agents. These results indicate that Salmonella contamination can persist in the lairage environment from one processing day to the next and that Salmonella is present on red meat carcasses, although the implications of residual lairage contamination on carcass meat microbiology are not clear from this study. Abattoir owners should take steps to reduce the level of contamination in their premises to prevent contamination from being carried over from one processing day to the next.     

Prevalence and risk factors for bruises in Chilean bovine carcasses

Records of cattle slaughtered at two Chilean slaughterhouses (SLH1 and SLH2) were used to determine prevalence and risk factors for carcasses with bruises. Bruise prevalence amounted to 12.3% but differed between slaughterhouses (20.8% for SLH1 and 8.6% for SLH2 respectively). Bruise severity grade 1 (mild) was most frequently recorded. The type of the animal, source of animal, the level of fat cover and lairage time were associated with the presence of bruises. Older categories of animals and animals that pass through a market before being moved to the slaughterhouse are more prone to show bruises. The results also indicate that under the reported Chilean circumstances animals that have longer lairage times (over 12 h) have a significantly reduced risk for bruises, except for oxen. Presence of bruises is also significantly associated with increased carcass pH values.     

Effects of mid-summer transport duration on pre- and post-slaughter performance and pork quality in Mexico

Seven hundred and fourteen pigs were monitored from transport to slaughter in July in three treatments: 8, 16 and 24 transport hours; lairage time for the three groups was of 8h. Transport duration significantly (P<0.05) affected live-weight gain during the rest period. Weight gain percentages at lairage were 0.05%, 0.78% and 1.15% for treatments 1, 2 and 3, respectively. Transport to slaughter loss percentage was 2.7%, 4.3% and 6.8% for each of the treatments. Short transport periods significantly increased carcass pH below normal values. Animals transported under acute stress (8h) showed pale carcasses (high possibilities of transforming into PSE meat). On the contrary, pigs transported for 24h had more dark red carcasses. Transport from farm to the slaughterhouse should take no more than 16h in order to improve carcass quality and animals' welfare.     

Objective meat quality measurements of ham: A practical classification method on the slaughterline

Meat quality is one of the principal problems in Spanish dry cured ham productuon. At the experimental level, there are well developed objective instrumental measurements which can be made on the slaughterline and then, by applying the correct statistical treatment, these measurements can be used to classify hams with an acceptable degree of accuracy. These treatments, however, are not easy to apply in the industry.

In this work, 312 pork carcasses were tested at three industrial abbatoirs. Ham meat quality was determined by internal light scattering (FOP), electrical conductivity (EC) and pH measurements in Semimembranosus (SM) muscle at 45 min and 24 h post mortem. The results obtained were: 21 (6.7%) DFD; 168 (53.9%) slightly DFD; 104 (33.3%) normal; 11 (3.5%) slightly PSE; and 8 (2.6%) PSE.

A simplified method has been developed for classifying hams into quality categories, by deriving a theoretical quality value (Q) based on a simple statistical treatment of values for FOP, EC and pH. The multiple linear regression coefficient of Q was R² = 0.85 (P<0.001) with respect to the experimental variables.     

The variation in pig muscle glycolytic potential during lairage-an in-vivo study

The variations in glycolytic potential (GP, very close to glycogen content) were studied during lairage in pig m. longissimus dorsi using biopsy sampling. Pigs were sampled on arrival at the abattoor and after treatment. Post-mortem measurements including pH(1), pH(u) and FOP(u) were performed on both longissimus dorsi (LD) and biceps femoris (BF) muscles. The animals underwent one of the following treatments: 2 h lairage mixed or unmixed; 24 h lairage mixed or unmixed with access to water only; 24 h lairage mixed or unmixed with access to a sugar solution. A significant depletion in GP occurred during lairage except when pigs were fed liquid sugar. The extent of this depletion was irrespective of lairage duration or mixing. Pigs lairaged 24 h with access to water only exhibited a significantly lower pH(1) in m. BF suggesting a higher propensity to develop PSE meat. Values of pH(u) were low (pH < 5·5), and did not vary significantly between the treatments since muscle GP remained high, despite the depletion induced by lairage. This was attributed to the high level of muscle glycogen characterizing the Hampshire crossbred pigs used in this experiment. These results suggest that interaction between breed and handling procedure may be important regarding meat pH(u).