clipped together using metal binder clips to prevent water in the chiller from contacting the breast muscle (McKee and Sams, 1997). Also, muscle samples from ...
The Use of Halothane Gas to Identify Turkeys Prone to Developing Pale, Exudative Meat When Transported Before Slaughter1 C. M. Owens,* N. S. Matthews,† and A. R. Sams*,2 *Department of Poultry Science and †Department of Small Animal Medicine and Surgery, Texas A&M University, College Station, Texas 77843 to slaughter, all birds were transported in coops on a flatbed trailer for 2 h and then immediately slaughtered upon arrival at the processing plant. Breast muscle pH (0, 1.5, and 24 h postmortem) and L* value (1.5 h and 24 h postmortem) were measured on the fillets. Drip loss and cook loss were also determined on marinated and nonmarinated breast fillets from each carcass. There were no significant mean differences in any parameter measured between the HAL+ and HAL− turkeys. However, the HAL+ turkeys had a greater percentage of fillets with L* values >51 compared with the HAL− turkeys. These results suggest that either halothane response is only a limited predictor of PSE meat in turkeys or that transportation is not an appropriate stressor to induce the PSE condition.
ABSTRACT Halothane screening has been used in the swine industry to identify animals susceptible to stress and prone to developing pale, soft, exudative (PSE) meat. This study evaluated the ability of halothane to identify stress-susceptible turkeys prone to developing PSE meat when reared to market age and transported before slaughter. Male Nicholas turkeys (n = 1,286) were exposed to 3% halothane for 5 min at 4 wk of age in two trials. Birds were classified as halothane sensitive (HAL+) or halothane nonresponder (HAL−), in which HAL+ birds showed signs of muscle rigidity in the legs upon removal from halothane gas, and HAL− birds showed no stiffness response. Approximately 3.5% (45) of the turkeys were HAL+. All HAL+ birds and an equal number of HAL− birds were grown until 20 wk of age. Immediately prior
(Key words: pale, soft, exudative; halothane; transportation; turkey; meat quality) 2000 Poultry Science 79:789–795
or cold), transportation, preslaughter handling practices, stunning methods, and chilling regimes can contribute to the development of PSE meat by increasing muscle metabolism, maintaining high temperatures, or both (Cassens et al., 1975; Honikel, 1987; Offer, 1991; Backstrom and Kauffman, 1995; D’Souza et al., 1998; Maribo et al., 1998). Specifically, transportation of animals has been shown to be stressful for animals as indicated by increased levels of β-endorphin, corticosterone, cortisol, and creatine phosphokinase (Szilagyi, et al., 1981; Freeman et al., 1984; Shaw and Tume, 1992; Bilgili et al., 1994; Geers et al., 1994; Kannan et al., 1997; Brown et al., 1998). However, its ability to induce PSE meat in turkeys is not known. Genetically, stress susceptible swine have a single-point mutation in the ryanodine receptor (calcium release channel) of the muscle (Fujii et al., 1991). In muscle contraction, a defective ryanodine receptor causes the channel to remain open, allowing a greater influx of calcium into the sarcoplasm (Mickelson and Louis, 1993). Because the channel is locked open, it is difficult for the calcium to be removed from the sarcoplasm to allow for relaxation of the muscle. Therefore, muscle remains in continuous
INTRODUCTION The development of pale, soft, exudative (PSE) meat has become a problem in the poultry industry. Meat with PSE characteristics is pale in color, has a low water-holding capacity, and forms soft gels (Sosnicki and Wilson, 1991; Barbut, 1993; Ferket and Foegeding, 1994; McKee and Sams, 1997, 1998; Rathgeber et al., 1999). The PSE meat has long been recognized in the swine industry and is strongly associated with animals that are genetically stress susceptible (Pommier and Houde, 1993). However, animals with normal stress tolerance can also develop PSE meat (Louis et al., 1993). The PSE meat develops because of protein denaturation that occurs when there is a fast decline in pH at early postmortem times when carcass temperatures are high (Penny, 1969; Warriss and Brown, 1987; Santos et al., 1994). Antemortem and postmortem factors such as environmental temperatures (hot
Received for publication July 21, 1999. Accepted for publication December 14, 1999. 1 This research funded by a grant from US Poultry and Egg Association. 2 To whom correspondence should be addressed: asams@poultry. tamu.edu.
Abbreviation Key: HAL+ = halothane sensitive; HAL− = halothane non-responder; HS = heat stressed; PSE = pale, soft, exudative.
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contraction, resulting in increased muscle metabolism. The gene responsible for the defective ryanodine receptor is known as the halothane gene because swine with a defective receptor are also sensitive to halothane (Hall et al., 1980; Harrison, 1979). Because of this association, halothane has been used as a tool to screen and identify animals that are stress susceptible and are prone to developing PSE meat. The screening method has been successful in identifying homozygous recessive animals (Houde et al., 1993). Although the association between halothane sensitivity and the development of PSE meat is well understood in swine, little is known about the association in poultry. In addition, because turkeys are normally transported prior to slaughter, the transportation may be stressful to the animal and, consequently, influence meat quality. Therefore, the objective of this study was to determine whether screening young turkeys with halothane gas could identify turkeys prone to developing PSE meat when transported prior to slaughter.
FIGURE 1. Turkey classified as halothane sensitive (HAL+), exhibiting signs of muscle rigidity in the legs.
MATERIALS AND METHODS Two separate groups (trials) of 1-d-old male Nicholas turkey poults (n = 671 for Trial 1 and n = 615 for Trial 2) were obtained from a commercial grower. All of the birds in a trial were from the same hatch date, and the two trials were separated by 2 wk. Poults were grown until 4 wk old, using commercial growing practices. At 4 wk of age, the turkeys in each trial were challenged with halothane gas (Wheeler et al., 1999). Birds were placed in an air-tight chamber (five to nine birds per group, depending on size) and were exposed to 3% halothane gas in oxygen for 5 min using an oxygen flow rate of 6 L/min. All birds were anesthetized (unconscious) within 2 to 3 min of exposure to halothane. After exposure, turkeys were quickly removed and subjectively evaluated for muscle rigidity in the legs while the birds were still unconscious, similar to the subjective evaluations used in the halothane-screening procedures for swine (Eikelenboom et al., 1978; Webb and Jordan, 1978). If leg muscles were rigid, birds were classified as halothane sensitive (HAL+) (Figure 1), and if muscles were flaccid, birds were classified as a halothane nonresponder (HAL−) (Figure 2). A panel of the same three people made the evaluations throughout the halothane-screening procedures so that classifications would be consistent. After halothane screening, all of the HAL+ and an equal number of randomly selected HAL− turkeys from the same hatch group were grown until 20 wk of age (total n = 90). Birds were housed at ambient temperatures in litter-covered floor pens and were fed a commercial ration that met the nutritional requirements for turkeys (NRC, 1994). At 20 wk of age, birds were processed at the University’s pilot plant. Feed was withdrawn from turkeys, but the birds were provided water for 12 h prior to slaughter. Prior to processing, all turkeys were transported in coops on a flatbed trailer for 2 h to simulate commercial live haul conditions. Birds were immediately slaughtered
upon arrival at the processing plant. Preslaughter stunning was not used because it is not required by law for commercial poultry slaughter (Goodwin et al., 1961; Bilgili, 1992; USDA, 1997), is not universally practiced by commercial processors, and has been shown to interfere with rigor mortis development (Murphy et al., 1988, Papinaho and Fletcher, 1995; Poole and Fletcher, 1998; Craig et al., 1999). Turkeys were killed by bleeding for 3 min through a unilateral neck cut. Birds were then individually subscalded (61 C for 45 s) and picked (rotary drum
FIGURE 2. Turkey classified as halothane nonresponder (HAL−), exhibiting flaccid muscles (no signs of muscle rigidity) in the legs.
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picker,3 30 s). Birds were manually eviscerated, and carcasses were chilled (4 C for 75 min). Breast fillets (Pectoralis) were deboned at 1.5 h postmortem to simulate commercial deboning practices. Fillets were placed in plastic zipper-sealed bags and then aged on ice until 24 h postmortem. Muscle samples were collected from the cranial portion of the left breast fillets at 0, 1.5, and 24 h postmortem, immediately frozen in liquid nitrogen, and stored at −76 C for pH determination using the iodoacetate method (Jeacocke, 1977; Sams and Janky, 1986). Following collection at 0 h sample (collected immediately after feather removal), breast skin surrounding the breast fillet was clipped together using metal binder clips to prevent water in the chiller from contacting the breast muscle (McKee and Sams, 1997). Also, muscle samples from the Gastrocnemius in the leg were collected at 1.5 and 24 h postmortem, immediately frozen in liquid nitrogen, and stored at −76 C for muscle pH determination using the iodoacetate method. Muscle pH in the leg (Gastrocnemius) was measured because turkeys were classified as HAL+ or HAL− according to the reaction in their legs upon exposure to halothane. The L* value, a measurement of lightness of color, was measured on the cut surface of the left breast fillets at 1.5 and 24 h postmortem using a Minolta colorimeter.4 The colorimeter was programmed to average three color readings per fillet. A new cut was made prior to color measurement at both time points to avoid any surface changes caused by water or air contact with the muscle. The right fillets were weighed at time of deboning and at 24 h postmortem to determine drip loss. The right fillet was divided into four sections. The middle two sections were used for cook loss analysis, and the remaining sections (cranial- and caudal-most) were discarded. The cranial-most middle section of each fillet (approximately 7 to 10 cm wide and 350 to 450 g) was placed in pans on raised wire racks, covered with aluminum foil, and cooked to an internal temperature of 76 C in a convection oven5 (Sams, 1990). The fillets were weighed before and after cooking to determine cook loss. The caudal-most middle section of the fillet (approximately 7 to 10 cm wide and 350 to 450 g) was tagged for identification and then marinated with a 20% (solution weight:meat weight) marinade solution (94% water, 3.6% salt, 2.4% sodium tripolyphosphate6). Fillets were marinated in a vacuumtumbler7 at 10 rpm for 1 h in a vacuum (610 mm Hg). After marination, fillets were placed in plastic zippersealed bags and held overnight in a cooler at 4 C. The following day (48 h postmortem), marinated fillets were cooked using methods previously described. Fillets were weighed before and after marination and before and after
3
Model SP3055, Brower Corp., Haughton, IA 52631. Model CR-200, Minolta Corp., Ramsey, NJ 07446. 5 Model Zephaire-G, Blodgett Oven Co., Burlington, VT 05402. 6 Sodium Tripolyphosphate FG LIG, Ashland Chemical Co., Columbus, OH 43216. 7 Model MC-25, Inject Star, Brookfield, CT 06804. 4
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cooking to determine marinade uptake, retention, and cook loss of the fillets. Data were subjected to analysis of variance using the general linear model procedure of SAS (1985). The residual mean square error was used as the error term, and trials were pooled because no interaction was observed. Differences between means from HAL+ and HAL− turkeys were determined using the analysis of variance Ftest (SAS, 1985) and a significance level of P < 0.05. The percentages of pale fillets (L* >51) in each halothane response group were subjected to chi-square analysis to determine differences (P < 0.05). In addition, data from birds were classified as pale or normal based on meat color (L* value of 51). The L* values between 51 and 53 have previously been used as thresholds to detect pale meat (McCurdy et al., 1996; Barbut, 1997; McKee et al., 1998; Owens et al., 2000). Differences in means between the pale and normal groups were determined as previously described for the halothane response groups.
RESULTS AND DISCUSSION Approximately 3.5% (45/1286) of the turkeys exposed to the halothane gas exhibited signs of muscle rigidity in the legs. This response rate is similar to halothane response rates in previous studies. Wheeler et al. (1999) found that 2 to 15% of turkeys reacted to halothane exposure, whereas Owens et al. (2000) reported a 10% response by turkeys screened with halothane gas. In swine, halothane-positive frequencies typically range from 0 to 20% (Webb and Jordan, 1978); however, this frequency can be much higher in genetically stress-susceptible swine such as the Pietran breed (Louis et al., 1993). Although the association between halothane sensitivity and the defective ryanodine receptor is well understood in swine, little information is known about this association in poultry. A major difference between swine and poultry is that swine have one isoform of the ryanodine receptor in skeletal muscle, whereas poultry have two isoforms (Percival et al., 1994). It may be possible that if there is one (of two) defective ryanodine receptor in turkeys, the other may be unaffected and may be able to compensate for any defect in the first. Postmortem metabolism was monitored in this study by measuring muscle pH. The decline in pH after slaughter is a result of an increase in lactic acid concentration in the muscle (Khan and Nakamura, 1970; Lawrie, 1998). The animal’s inability to remove lactic acid from the muscle because of loss of the circulatory system and ongoing glycolysis results in an accumulation of lactic acid and, thus, a decrease in pH. A rapid decrease in muscle pH combined with high carcass temperatures, as in early postmortem times, can cause protein denaturation in the muscle (Bendall and Wismer-Pedersen, 1962; Penny 1969; Mitchell and Heffron, 1982; Offer, 1991). This denaturation leads to the increased paleness of the muscle and lower water-holding capacity, which are both characteristics of PSE meat (Bendall, 1973; Swatland, 1993). In the present study, there was no significant difference in breast
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OWENS ET AL. TABLE 1. Meat quality attributes of breast fillets from halothane+ and halothane− male turkeys
Attribute
Halothane+1
Halothane−1
SEM
Pectoralis pH 0h 1.5 h 24 h
6.24 6.06 5.98
6.25 6.10 6.00
0.01 0.02 0.02
Gastrocnemius pH 1.5 h 24 h
6.78 6.46
6.75 6.42
0.01 0.01
48.24 51.54 0.32 20.24 17.40 98.46 23.70
47.49 50.96 0.17 20.46 17.27 98.46 24.47
0.19 0.21 0.34 0.60 0.36 0.07 0.78
Pectoralis L* value 1.5 h 24 h Drip loss (%) Cook loss2 (%) Marination3 uptake (%) Marination retention4 (%) Marinated cook loss (%)
n = 45 per mean. Nonmarinated cook loss. 3 Marinated with 20% solution at 24 h postmortem. 4 Measured 24 h after marination. 1 2
muscle pH at any postmortem time period (0, 1.5, or 24 h) between HAL+ and HAL− turkeys (Table 1). In addition, there was no difference in leg muscle pH at 1.5 or 24 h between the treatments (Table 1). Previous research has indicated that HAL+ swine have a more rapid decline in muscle pH as indicated by lower pH values at 45 min postmortem compared with HAL− swine (De Smet et al., 1993; Cheah et al., 1994; Klont and Lambooy, 1995). The stress-susceptible swine, as identified by halothane, can easily be stressed prior to slaughter, resulting in an increase in the rate of metabolism that continues after death. This increase in metabolism leads to a rapid decline in pH and, consequently, problems with meat quality (pale and exudative). The effects of stress on muscle metabolism and the use of halothane screening in turkeys have been inconsistent. Owens et al. (2000) screened two genetic strains of turkeys with halothane and observed lower muscle pH at 0 h in heat-stressed (HS) HAL+ compared with HS HAL− turkeys in a strain selected for large breast yield, but there was no difference in muscle pH between HS HAL+ and HS HAL− turkeys selected for rapid overall growth. The commercial turkeys used in the present study were not subjected to elevated temperatures (heat stress) but were transported for 2 h immediately prior to slaughter. It may be possible that the transportation was not an appropriate stressor to induce an acceleration of postmortem metabolism. Although there were no differences in pH means between HAL+ and HAL− turkeys, turkeys with pale meat (L* > 51 at 24 h) had significantly lower pH (in the breast) at 1.5 and 24 h postmortem compared with turkeys with normal-colored meat (Table 2). This result suggests that some of the turkeys may have been susceptible to preslaughter stress or that the halothane-screening test may not be 100% predictive of the development of PSE meat.
Color is an important meat quality attribute and can be affected by antemortem and postmortem factors. The L* value, a measurement of lightness of color, is often used as an indicator of PSE meat. In addition, our laboratory has observed that L* value has a more predictive value of PSE turkey meat than muscle pH (Owens et al., 2000). Protein denaturation and paleness in the muscle can occur when there is a rapid decline in muscle pH combined with high carcass temperatures (Bendall and Wismer-Pedersen, 1962; Penny 1969; Mitchell and Heffron, 1982; Offer, 1991). In the present study, there were no differences in L* values at 1.5 or 24 h postmortem between the HAL+ and HAL− turkeys. Researchers have observed higher L* values in homozygous recessive (nn) swine (for halothane gene) compared with heterozygous (Nn) or homozygous dominant (NN) animals and have attributed those differences to differences in pH decline between the animals (De Smet et al., 1993; Lahucky et al., 1997; Stalder et al., 1998). In the present study, the lack of color difference between the treatments can be attributed to the lack of pH difference. However, when separating turkeys based on meat color, the turkeys with pale fillets (L* >51 at 24 h) had significantly higher L* values at 1.5 and 24 h postmortem than turkeys with normalcolored fillets (L* value 51 (71.1% vs. 51.1%) compared with the HAL− turkeys (Fig-
TABLE 2. Means of meat quality attributes of breast fillets based on meat color1 Attribute
Normal2 (L* Value 51)
SEM
Pectoralis pH 0h 1.5 h 24 h
6.26 6.12a 6.05a
6.23 6.05b 5.94b
0.01 0.02 0.02
Gastrocnemius pH 1.5 h 24 h
6.77 6.43
6.76 6.45
0.01 0.01
Pectoralis L* value 1.5 h 24 h
46.85b 49.26b
48.51a 52.52a
0.19 0.21
Drip loss (%) Cook loss4 (%) Marination5 uptake (%) Marination retention6 (%) Marinated cook loss (%)
0.15 19.63 18.55a 98.30 24.34
0.16 20.81 16.57b 98.54 23.92
0.34 0.60 0.36 0.07 0.78
a,b Means within row with no common superscript differ significantly (P < 0.05). 1 L* value measured at 24 h postmortem. 2 n = 35 per mean. 3 n = 55 per mean. 4 Nonmarinated cook loss. 5 Marinated with 20% solution at 24 h postmortem. 6 Measured 24 h after marination.
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In conclusion, there were no differences in any parameter between the HAL+ and HAL− turkeys that were transported for 2 h immediately prior to slaughter. However, the HAL+ turkeys had a greater percentage of pale meat (L* value >51) than the HAL− turkeys. The pale meat had lower breast muscle pH at 1.5 and 24 h postmortem and lower marination uptake, indicating that some of the turkeys had characteristics of PSE meat. Therefore, the results of this study suggest that either halothane response early in life is a limited predictor of PSE meat in turkeys or that transportation is not an appropriate stressor to induce the condition. Future research is still needed to determine the association between halothane sensitivity and meat quality of turkeys.
ACKNOWLEDGMENTS FIGURE 3. Percentage of pale fillets (L* value >51 at 24 h) from halothane positive (HAL+) and halothane negative (HAL−) turkeys (P < 0.05).
ure 3). Owens et al. (2000) also observed a greater percentage of pale fillets in HAL+ turkeys compared with HAL− turkeys. These results are consistent with the suggestion that either transportation is not an appropriate stressor to induce PSE condition in all of the HAL+ turkeys or that the halothane test is only a limited predictor of PSE meat in the turkeys. Water-holding capacity is another aspect of meat quality that can be affected in PSE meat. Therefore, drip loss, cook loss, and marination attributes were evaluated. Protein denaturation as previously discussed can lead to a loss in water-holding capacity. In the present study, there were no differences in drip loss, cook loss, marination uptake, retention, or cook loss of marinated fillets. This lack of differences in water-holding capacity between HAL+ and HAL− turkeys may be due to a lack of a pH difference. Although there were no differences between HAL+ and HAL− turkeys, marination uptake was significantly lower in turkeys with pale fillets compared with turkeys with normal-colored fillets. There were no other differences in water-holding capacity between pale and normal-colored fillets. It is possible that the pale meat had slightly lower protein functionality because of its lower pH, resulting in lower uptake of the marinade. However, the proteins may have not been damaged to the point at which cook loss was affected. Previous research has indicated that homozygous recessive (nn) (halothane gene) swine have decreased water-holding capacity as measured by drip loss and cook loss (Cheah et al., 1994; Klont and Lambooy, 1995; Lahucky et al., 1997; Stalder et al., 1998; Monin et al., 1999). Other researchers have reported that transportation increases water-holding capacity as a result of a depletion of muscle glycogen and, subsequently, higher postmortem muscle pH (van Hoof, 1979; Becker et al., 1989, McPhee and Trout, 1995). It may be possible that water-holding properties were not affected in this study because of transportation.
The authors wish to thank Nicholas Turkey Breeding Farms and Plantation Foods for their support of this project.
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