The effects of porcine somatotropin on muscle fibre morphology and meat quality of pigs of known stress susceptibility

Meat Science,Vol. 45, No. 3, 283-295, 1997 OZ 1996Elsevier Science Ltd PII:

SO309-1740(96)00111-8

All rights reserved. Printed in Great Britain 0309-1740/97 $17.00+ 0.00

ELSEVIER

The Effects of Porcine Somatotropin on Muscle Fibre Morphology and Meat Quality of Pigs of Known Stress Susceptibility J. L. Aalhus, D. R. Best, F. Costello & A. L. Schaefer Meat Research Section, Lacombe Research Centre, Agriculture and Agri-Food Canada, Lacombe, Alberta, Canada T4L 1W 1 (Received 29 May 1996; revised version received and accepted 3 September 1996)

ABSTRACT To study the eflects of porcine somatotropin (PST) administration on muscle jibre characteristics and meat quality, 48 pigs of the Lacombe breed (equal numbers of barrows and gilts) of known halothane genotype (NN, Nn or nn) were randomly assigned to either a control (excipient buffer) or PST (3.0 mg d-r) treatment. At a pen average animal weight of 106 kg, pigs were slaughtered and muscle samples were collected post mortem for determination of jbre type, glucidic metabolites and meat quality. There was a 16% increase in muscle weight of the semimembranosus (SM) and psoas major (PM) in PST-treated animals (p 5 0.01). However, there was no signtficant change in fibre type associated with the PST treatment in either the SM or PM (p > 0.05). In the PM muscle there was a 65-70% increase in fast, oxidative, glycolytic (FOG) and fast, glycolytic (FG) Jibre areas in PSTtreated gilts (p 5 0.05). These cellular changes were mantfest in meat colour that was lighter and spectraBy shifted towards yellow (signt$cantly higher L’ and hue angle values), higher drip loss, lower moisture content and a tendency towards higher Kramer-Press shears (p = 0.06) in the PM of PST-treated gilts. Although these changes were in the same direction as pale, soft, exudative meat, the average values fell within the normal range. Based on the observed gender by PST treatment interactions, administration of PST (timing, dosage and protein requirements in the feed) may need to be tailored to suit dtferent genders and breeds to achieve the maximal response. 0 1997 Elsevier Science Ltd. All rights reserved

INTRODUCTION of porcine somatotropin (PST) is known to improve carcass composition through a reduction in body fat with a concomitant increase in muscle mass (Etherton et al., 1987; Campbell et al., 1988). Initially, most studies reported that the increase in muscle mass was due to an increase in muscle fibre size only, with no effect on the relative frequencies of muscle fibres (Solomon et al., 1988; Beermann et al., 1990). However, more recent reports in the literature suggest that muscle fibre distribution may be affected by the PST treatment in boars and gilts, but not barrows (Solomon et al., 1990) and over a weight range of 3&90 kg (Solomon et al., 1991). Since ultimate meat quality can be affected by muscle fibre composition (Cassens & Cooper, 1971; Aalhus & Price, 1991), it is important to characterize the changes in fibre type associated with PST treatment. Administration

283

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In several papers Solomon et al. (1988, 1990, 1991) noted the presence of so-called ‘giant’ fibres in PST-treated pigs. The occurrence of giant fibres has been demonstrated in stress susceptible pigs, which yield pale, soft, exudative meat (PSE) (Bader, 1987). Solomon et al. (1991) indeed reported an increased incidence of PSE, with 62% of PST-treated pigs exhibiting PSE. In contrast, Beermann et al. (1990) reported no such increase in PSTtreated pigs. However, the results of Solomon et al. (1988, 1990, 1991) were not conclusive since the pigs used in his experiments were of unknown genotype, so it is possible that the giant fibres observed in these studies resulted from stress susceptibility, independent of the PST treatment. The purpose of this study was to examine the effects of pST on muscle fibre morphology and meat quality in two muscles which vary widely in their initial fibre type composition (m. psous major and m. semimembrunosus). Animals of known genotype with respect to stress susceptibility were used to separate the effects of pST from those of stress susceptibility.

MATERIALS

AND METHODS

The animals used in this study were raised and slaughtered in accordance with the principles and guidelines set out by the Canadian Council on Animal Care (1984). The study was conducted under a Canadian Investigation of New Drugs licence No. 5379 and was part of a larger study on the efficacy of PST (Dugan et al., in press). One hundred and forty-four pure-bred Lacombe pigs (equal numbers of barrows and gilts) were classified with respect to the halothane gene (NN, halothane negative; Nn, heterozygous; and nn, halothane positive) as described by Murray & Jones (1994). Animals were blocked into three weight groups and assigned to one of 12 pens within a weight group. Animals were housed in groups of four, separated by sex and genotype. On a random basis half the pens were assigned to either a control (excipient buffer) or PST (3.0 mg dd’ solubilized in 0.6 ml saline) treatment. Daily injections were administered subcutaneously at the base of the ear for a minimum of 42 days. Animals were fed ad libitum a barley/wheat/soybean meal ration containing a minimum of 16% protein, 0.5% calcium and 0.4% phosphorus (Dugan et al., in press). Schricker et al. (1989) had previously established that 3.0 mg PST per day optimizes growth performance in pigs fed diets containing greater than 16% crude protein. For the present study, only two animals per pen from two weight blocks (designated as animals for full carcass cut-out) were sampled, for a total of 48 animals (four animals per genotype by sex by treatment cell). When a pen average animal weight of 106 kg was reached, pigs were removed from feed, transported to the Lacombe Meats Centre (5 min by truck) and held in lairage, with free access to water, for a minimum of 1 h prior to slaughter. Pigs were stunned with head to back electrodes (400 V for 2-3 s), shackled, exsanguinated, scalded and eviscerated. Immediately prior to splitting the carcass, at 30 min post mortem, muscle cores (approximately 200 g) were removed using a 37 mm cork borer from the right m. semimembrunosus (SM) and m. psous major (PM), and quick-frozen in liquid nitrogen for later determinations of glucidic metabolites and buffering capacity. At 40 min post mortem pH and temperature were recorded for the left SM (approximately 3 cm from the tip of the aitch bone) and PM (at the third lumbar vertebra) muscles with a HI8424 pH meter (Hanna Instruments, Singapore) equipped with a Xerolyt spear-type probe (Ingold Messtechnik AG, Urdorf, Switzerland). The carcass sides were chilled for 24 h at 2°C. Following chilling, 24 h pH and temperature readings were again recorded for the left SM and PM. Muscles were removed from the right side of the carcass and small samples

PST and stress susceptibility

285

were removed from standardized locations, mounted on cryostat chucks perpendicular to the grain of the muscle fibres and quick-frozen in isopentane cooled in liquid nitrogen for fibre type determinations. As the left carcass sides were dissected into the major tissue depots, the left SM and PM were collected. A 35 mm chop from each muscle was weighed into a polystyrene tray, over-wrapped with oxygen permeable film and stored for 2 days at 4°C to determine drip losses. The remaining portions of the left SM and PM, and right PM were stored overnight at 2°C in a polythene bag. The following day (at 48 h post mortem), a 38 mm chop was cut from the left SM and PM. While the meat was blooming for 15-20 min, ultimate pH and temperature were determined on the remaining portions of the muscles. Following the time allowed for blooming, meat color was measured three times on the chop, using a Chroma-Meter II (Minolta Canada Inc., Mississauga, ON). Three meat colour values (CIE L’ (brightness), a* (red-green axis) and b’ (yellow-blue axis; Commission Internationale de l’Eclairage, 1976) were measured and the results were converted to hue (Hab = arctan[b*/a*]) and chroma (C,, = [a** + b*2]o.5) prior to averaging. The SM chop was then cooked to an internal temperature of 72°C (monitored with an electronic temperature probe; Technoterm 1100, FRG) in a microwave oven. Following cooking the chop was cooled on ice and stored overnight at 2°C. Shear force (perpendicular to the muscle grain) was determined on three 19 mm cores with an Instron 4301 Material Testing System (Burlington, ON) equipped with a Warner-Bratzler head. For the PM, the anterior portion of the right PM muscle was cut into chops, cooked similar to the SM, cooled overnight at 2°C and coarsely ground through a 3-mm grinding plate the following day. Three 10-g subsamples were tested on the Instron 4301 equipped with a Kramer shear compression cell. The remaining portions of the left SM and PM were chopped into pieces and ground twice through a 3-mm grinding plate. Moisture content was determined as the weight lost after heating of the ground tissue at 110°C for 24 h. Protein solubility was measured on the frozen samples as described by Barton-Gade (1985), except that the result was expressed as grams soluble protein per kg of lean muscle, instead of as optical density (Murray et al., 1989). Glucidic metabolites were extracted using the frozen SM and PM muscle cores (collected at 30 min post mortem) according to the procedure of Dalrymple & Hamm (1973). Metabolite concentrations were determined as outlined in Bergmeyer (1971). Glucidic potential was calculated as the sum of glucose, glucose-6-phosphate, glycogen and onehalf the lactate concentration. Buffering capacity was determined on sub-samples of the frozen SM and PM muscle cores according to the method of McCutcheon et al. (1987) modified for use with larger samples. For fibre type determinations, 10 pm sections were stained for myosin ATPase and succinate dehydrogenase using the combined procedure of Solomon & Dunn (1988). Photomicrographs of the slides were developed and the frequency of fibre types (slowoxidative, SO; fast-oxidative-glycolytic, FOG; fast-glycolytic, FG; and giant, G) were determined for two muscle bundles (approximately 50 fibres were counted per sample). Both the minimum and maximum diameters were measured for each fibre type and converted to an equivalent cross-sectional area using the formula developed by Clancy & Herlihy (1978). Adjacent fibres were measured within a bundle for a total of 10 fibres (where possible) of each fibre type per animal. Statistical

analysis

Separate statistical analyses were performed on each muscle using a model which included the effects of genotype, gender, treatment and their two-way and three-way interactions. Data were analysed using the multiple linear regression subset of the General Linear

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Model computer algorithm of the Statistical Analysis System, Version 5 (SAS, 1985). Linear contrasts with one degree of freedom were used for means separation @ 5 0.05).

RESULTS

AND DISCUSSION

Effects of PST There was no significant change in fibre type distribution associated with the PST treatment in either the SM or the PM muscle (Fig. 1). The majority of previous studies have reported no change to fibre type distribution (Beermann et al., 1990; Rehfeldt & Ender, 1993; Oksbjerg et al., 1995; Ono et al., 1995). However, a series of papers by Solomon and co-workers noted an increase in the proportion of FOG fibres and a decrease in proportion of FG fibres in the longissimus muscle (Solomon et al., 1990; 1991). In contrast, Whipple et al. (1992) reported a decrease in the proportion of FOG fibres and an increase in the proportion of FG fibres. Part of this discrepancy may be due to the fact that Solomon and his co-workers did not include the G fibres which they observed in their calculation of muscle fibre frequencies. Hence, if the G fibres arise as a pathological postmortem alteration of existing FG fibres (Bader, 1987; Rehfeldt & Ender, 1993), the apparent proportion of FG fibres may decrease with a corresponding increase in FOG fibres. In addition, it has been suggested by Ono et al. (1995) that the influence of PST may depend on the stage of maturity of individual muscles. Normal changes in fibre type associated with maturity are an increased proportion of FG fibres and a decreased proportion of FOG and SO fibres (Rehfeldt & Ender, 1993), similar to the results associated with pST treatment reported by Whipple et al. (1992). However, since a number of different breeds, genders and muscles, all with different rates of maturity, have been

nG cl FG tzl FOG n so

7 Semimembranosus Fig. 1. Distribution

Psoas major

of SO (slow, oxidative), FOG (fast, oxidative, glycolytic), FG (fast, glycolytic) and G (giant) fibres in the semimembranosus (SM) and psoas major (PM) muscles.

pST and stress susceptibility

287

investigated in the papers cited (Table l), it may be that differences in maturity (or growth rates) are reflected in the variable response to PST. There was no indication that PST resulted in an increase in the proportion of G fibres (Fig. 1). Similarly, Whipple et al. (1992), Lefaucheur et al. (1992) and Rehfeldt & Ender (1993) did not find an increased incidence of G fibres in PST-treated pigs. Hence it is possible that the observed increase in the proportion of G fibres in the studies by Solomon and his co-workers was due to the undetected presence of the halothane gene in the population of Duroc/Landrace cross pigs used in their experiments. This may also contribute to the changes in the proportion of FOG and FG fibres associated with PST treatment in their studies (Solomon et al., 1990, 1991), since changes in the proportion of fibre types are inherent with the halothane gene (see Fig. 1). Rehfeldt & Ender (1993) suggested that the results of Solomon and co-workers were due to breed differences in the response to PST. For most traits there was a limited response to PST, with the most consistent effect a gender by PST interaction (Tables 2 and 3). In the SM muscle, there were no significant gender by PST treatment interactions for the different muscle fibre type areas, whereas in the PM muscle there was a 65-70% increase in FOG and FG fibre areas in PST-treated gilts (p 5 0.05; Table 2). All previous studies have reported some degree of radial hypertrophy associated with PST administration. In some cases a general hypertrophy of all fibre types was reported from a minimum of 5% (Oksbjerg et al., 1995) to a maximum of 34% (Solomon et al., 1991). In other cases, radial hypertrophy was only reported in certain muscles or fibre types (Whipple et al., 1992; Solomon et al., 1994; Ono et al., 1995). Again, the variable response to PST among different studies is likely due to breed, gender and muscle differences in maturity or due to dissimilarities in the experimental design (dosage levels of PST, ration composition, etc.). The glucidic potential of PST-treated barrows was higher than controls in both the SM and PM muscles (p < 0.05 and p = 0.08, respectively; Table 2). In addition, there was a tendency for increased lactate production in PST-treated barrows in the PM muscle (72.6 vs. 62.9 mM gg’; p = 0.09). However, no significant influence on metabolite concentrations occurred in PST-treated gilts, despite the fact that muscle fibre morphology was significantly affected in the PM muscle of PST-treated gilts. Oksbjerg et al. (1995) found no increase in the activity of lactate dehydrogenase or citrate synthetase associated with administration of PST in muscle biopsy samples. However, Oksbjerg et al. (1995) also observed one of the least responses to PST (only a non-significant 5% increase in muscle fibre area). Using similar sampling procedures to the present study (muscle samples collected post mortem), Lefaucheur et al. (1992) reported a significant increase in the lactate dehydrogenase : citrate synthetase ratio (a shift towards a more glycolytic metabolism) in samples from the semispinalis muscle but not in the longissimus muscle. The semispinalis muscle is a highly oxidative muscle compared with the longissimus, as is the PM compared with the SM. Hence, it appears that only muscles which are highly oxidative respond to PST by shifting to a more glycolytic metabolism. Despite fairly minimal PST-induced cellular changes, there was a significant 16% increase in muscle weight of the SM (1005 vs. 866 g) and PM (332 vs. 286 g) in PSTtreated animals compared with controls (p 5 0.01). In addition, there were a number of PST by gender interactions in the meat quality traits (Table 3). In both the SM and PM muscles, PST-treated barrows had significantly higher ultimate pH values than controls, In the SM, the higher ultimate pH was associated with a darker meat colour as expressed by a tendency towards lower L’ values (p = 0.07) and significantly lower hue angle and chroma values @ < 0.05). However, in the PM muscle, although the values for L*, hue angle and chroma were numerically lower in PST-treated barrows than controls, none of these differences approached significance. In contrast, in the PM muscle of gilts, PST

Barrow

Barrow

et al., 1991

etal., 1992

Solomon

Whipple

Barrow

Barrow and gilt

etal., 1990

Beennan”

etal., 1992

Barrow gilt and

etal., 1990

Solomo”

Large White

Hamp x York x Chester White

Duroc x York

L/yX Doroc

45

30

24

80

37

34

?

Barrow

Solomon et al., 1988

Duroc x York

NO.

Breed

sex

Author

Lefaucheur

TABLE

1

OorlOO @g/kg/day

0 or 4 mg/ day

OorlOO pglkglday

0, 30, 60, 120 or 200 @g/kg/ day

OorlOO fig/kg/day

OorlOO pglkglday

Treatment

LT, SM

LM

ST, LM

LM

Overall mea” CSA t 2 1% with the exception of intermediate fibres in the LM t FG and 1 SO fibres in SS Did not f giant fibres t LDH:CS in SS More glycolytic, less oxidative in ss

t CSA in all fibre types: by 34% at 60 kg, and by 29% at 90 kg t FOG and G tibres and 1 FG fibres at both 60 and 90 kg No change in fibre diameters 1 FOG and t FG fibres in the LT; no change in the SM No G fibres observed

t pH 24 and glycolytic potential in SS No significant effect on pH, glycolytic potential or reflectance in LM

No effect on subjective colour score, firmness or exudation in LM Slightly darker based on objective measures in LM pHult was higher in LM 62% of PST treated pigs exhibited PSE Shear force t 30% at 60 kg and t 19% at 90 kg

7 visual PSE score Shear force 7 29.5% in barrows, and 1 by 13.9% and 17.1% in boars and gilts

Shear force f 17.1% No visual indication of PSE

t CSA in all fibre. types Noted presence of G fibres in PST-treated pigs No change in distribution of tibre types t CSA by 9.3, 31.8, 21.8% in boars, barrow and gilts, respectively t CSA by 28.4, 18.3, 20.7% in SO, FOG and FG tibres, respectively No effect on fibre distribution in barrows t FOG and 1 FG fibres in boars and gilts t CSA in all fibre types by 16% in ST No change in distribution of fibre types in ST

Meat quality

Histology/metabolites

MU.WkS

LM

3&100 kg or LM, SS 6&100 kg

58-105 kg

3060 or 90 kg

46-100 kg

6&90(?) kg 32 days

2555 kg

WT range

Summary of Recent Research on the Effects of PST at the Cellular Level

York x Duroc x Landr

Pal Ch x Landr

York x

BarKW

BarKW

Gilt

Solomon et al., 1994

On0 el al., 1995

Oksbjerg et ul., 1995

00~100 fig/kg/day

0 or 80 tip/ kg/day

20

00rlOO pg/kg/day

0.2 or 4 mg/day

28

60

60

5&86 kg

2&90 kg

45-100 kg approx. from 120 to 200 days 3&80(?) 42 days

LM, PM, PP, sv, TB, SP, IF, SB.BF. Ski, RF, GC LM, GM, PM

LM, SM, ST, TB

LM

Overall mean CSA 1 I I % No change in distribution of fibre types No T in G fibres t CSA in FOG and FG fibres in the LM, SM, TB T CSA in SO, FOG and FG libres in the ST t FOG and 1 FG fibres in ST; no change in LM, SM, TB r CSA in FG fibres in SV, BF, SM and GC No change in distribution of libre types Poor response possibly due to protein limitations in diet Overall mean CSA t 5.3% No change in frequency or % area of fibre types No change in muscle glycogen, or in activity of LDH, CS and HAD

Shear force, sarcomere length and eating quality were unchanged in LM pH 45 was lower in LM

Shear force t 13% in LM

Shear force t 12%

Breed abbreviations: York, Yorkshire; L/Y, Landrace/Yorkshire; Hamp, Hampshire; Landr, Landrace; Pol Ch, Poland China. Muscle abbreviations: LM, longbsimus muscle; PM, psoas major; SM, semimembranosus; SS, semispinalis; ST, semitendinosw; TB, triceps brachii; PP, pectoralis profindas; SV, serrates ventralis; SP, supraspinatus; IF. infraspinatus; SB, subscapularis; BF, biceps femoris; RF, rectusfemoris; GC, gastrocnemius. Fibre type abbreviations: SO, slow oxidative (red fibres); FOG, fast, oxidative glycolytic (intermediate fibres); FG, fast, glycolytic (white fibres); G, giant fibres. Other abbreviations: CSA, cross-sectional area; LDH, lactate dehydrogenase; CS, citrate synthetase; HAD, 3-OH-acyl-CoAdehydrogenase; PSE, pale, soft and exudative meat.

Landr

Landr

BarKW

Rehfeldt & Ender, 1993

G $ z 9

4 R

2 a. 4 ;;: z

:

+u

J. L. Aalhus et al.

290

treatment resulted in a numerically lower pH4s, a meat colour that was lighter and spectrally shifted towards yellow (significantly higher L’ and hue angle values), higher drip loss, lower moisture content, a tendency towards higher Kramer-Press shears (p = 0.06) and numerically lower soluble proteins. Although these changes are in the same direction as classic PSE meat, the average values still fall within the normal range. However in the PM, three PST-treated gilts had soluble proteins < 12%, whereas in the controls all gilts had soluble proteins > 13%. Soluble proteins lower than 12% are usually indicative of the PSE condition (A. C. Murray, pers. comm.). These changes towards a paler and more exudative meat are probably caused by the significant increases in cross-sectional area of FOG and FG fibres which we observed in the PM of PST-treated gilts. Other researchers have reported similar, gender specific effects of PST on meat quality (Table 1). Two studies, one using barrows and gilts, and the other using barrows only, reported a higher ultimate pH as a result of PST administration (Beermann et al., 1990; Lefaucheur et al., 1992) similar to the higher ultimate pH observed in the SM and PM of barrows in the present study. However, in their all-gilt study, Oksbjerg et al. (1995) observed a significantly lower pH4s as a result of PST administration. This is similar to the numerically lower pH4s observed in the PM of gilts in the present study. Despite these changes in pH, only Solomon et al. (1990, 1991) reported an increased incidence of PSE. As was the case with our data, perhaps in other studies an increased incidence of PSE as a result of PST administration can be masked by gender effects and by consideration of only the mean values. Certainly, several studies have reported an increased shear force, ranging TABLE 2

Gender by PST Treatment Means (SE) for Metabolite Concentrations and Muscle Fibre Type Areas in the Semimembranosus and Psoas major Muscles Semimembranosus Barrows

Gilts Control

Psoas major

PST

Control

PST

Gilts Control

Barrows pST

Control

PST

Metabolites (mM g-l) Glycogen Lactate Glucidic potential Buffering capacity= Flbre areasd (pm) so FOG FG G

25.9 (3.80) 42.3 (4.84) 49.3” (3.00) 82.8 (1.36) 2238 (210) 2336 (229) 4198 (420) 6868 (991)

23.9 (4.14) 42.1 (5.29) 46.8* (3.21) 85.4 (1.41) 2201 (210) 2421 (229) 6006 (420) 8254 (1113)

24.7 (4.14) 41.5 (5.29) 48.1” (3.21) 85.8 (1.48) 2391 (221) 2664 (241) 5554 (442) 8411 (1267)

32.3 (4.14) 41.1 (5.29) 59.0b (3.21) 88.5 (1.48) 2358 (221) 3022 (241) 5533 (442) 8697 (917)

(El) 67.2 (4.86) 46.9 (2.69) 80.8 (2.11) 1222 (157) 1101” (162) 2126” (383) 3237 (906)

(EO) 59.0 (5.03) 42.2 (2.18) 83.3 (2.25) 1353 (154) 1851b (159) 35116 (375) 3754 (576)

(E8) 62.9 (5.81) 40.8 (3.21) 81.3 (2.60)

1491 (195) 1484ab (201) 33146 (475) 5404 (888)

(E9) 12.6 (5.31) 46.1 (2.93) 84.1 (2.31)

1344 (169) 1460” (174) 2610ab (411) 4162 (815)

&Means within a muscle which are followed by different superscripts are significantly (p I 0.05). CBuffering capacity is expressed in pmol HCl per unit change in pH. %O, slow oxidative; FOG, fast, oxidative glycolytic; FG, fast, glycolytic; G, giant.

different

PST and stress susceptibility

291

from 12-30%, as a result of PST administration (Solomon et al., 1988, 1990, 1991, 1994; Rehfeldt & Ender, 1993). Generally, PSE pork arising from the halothane gene has higher shear values (Minelli et al., 1995), although the mechanism of this toughening effect is unknown at the present time (Aalhus et al., 1995). Effects of genotype The presence of the halothane gene resulted in a shift towards a more glycolytic fibre type (Fig. 1; Table 4). In the SM muscle there was a significantly lower proportion of SO fibres and a significantly higher proportion of G fibres in the nn and Nn compared with the NN genotype. In addition, there was a numerically larger proportion of FG fibres in the nn and Nn compared with the NN genotype (73.8, 74.4 vs. 70.9%). In the PM muscle, there was a significantly larger proportion of FOG fibres and a correspondingly smaller proportion of SO fibres in the nn compared with the NN genotype. The most extreme differences in muscle fibre areas were observed in the PM; nn animals had significantly larger SO, FOG and G fibre areas compared with NN animals (59,60 and 51%, respectively). In the SM, there were no significant differences in fibre area, however, SO and FOG fibres were 20% larger in the nn compared with the NN genotype. There have been relatively few recent papers reporting on the effects of the halothane gene on fibre type distribution and morphology. In most historical cases, the results related to pigs that were of a PSE-susceptible breed or that had been tested using the halothane challenge test; both techniques fail to segregate animals into halothane genotypes with a high degree of accuracy. Pigs used in the present study were from known genotypic lines developed at Lacombe (Murray & Jones, 1994). Using the blood marker technique (Gahne & Juneja, 1985) for identification of the halothane genotype, Es&n-Gustavsson TABLE 3 Means for Quality Traits in the Semimembranosus and Psoas major Muscles

Gender by PST Treatment

Semimembranosus Gilts Control

pST

Psoas major

Barrows

Gilts

Control

PST

SE

Control

6.04 40.0 5.40” 54.1 21.gb 13.gb 39.5

6.13 39.9 5.416 51.9 24.5” 12.0” 38.9

0.084 0.35 0.020 0.96 0.94 0.43 0.31

5.75 36.2 5.5gb 46.5” 19.4” 20.3 16.5”

pS?

Barrows Control

PST

SE

Quality traits ~H45 Temp4s

PH,I, CIE L’ Hue angle Chroma Drip loss ‘;;ei;) Moisture (mg g-‘) Soluble protein (mg g-‘)

5.96 40.3 5.45”b 52.9 25.Yb 13.gb 43.1

5.92 40.5 5.43”b 54.2 21.7b 14.0b 48.5

5.54 36.1 5.51”b 49.lb 22.3b 21.2 30.lb

5.61 5.65 36.7 36.5 5.41” 5.61b 49.1ab 41.3ab 21.50b 19.60b 20.2 19.6 23.3ab 19.2ab

0.079 0.54 0.038 0.98 1.09 0.65 4.09

8.93 8.46 8.74 8.37 739 743 738 145

0.332 3.13 3.18 2.1 752b 742”

3.51 3.50 152’ 7506

0.185 1.86

185

5.2

161

6.1

176

182

189

167

150

165

abMeans within a muscle which are followed by different superscripts are significantly different fp 5 0.05). ‘For the SM muscle, Warner-Bratzler shears in kg; for the PM muscle, Kramer-Press-Ground compressions in kg/g.

292

J. L. Aalhus et al.

et al. (1992) reported no difference in the proportion of fibre types associated with the halothane gene in the longissimus muscle. However, similar to the present study, they reported significant increases in fibre areas, with a maximum effect in SO and FOG fibres (100 and 72% larger, respectively). With the identification of the halothane mutation as the ryanodine receptor (Fujii et al., 1991), it is now possible to easily and accurately identify specific halothane genotypes using a genetic probe. Thus, further studies of pigs of known genotype will confirm the effect of the halothane gene on fibre type. The difference in fibre type morphology in the present study was manifest in a more rapid rate of glycolysis in the nn and Nn halothane genotypes (Table 4). By 30 min post mortem (when sampling of the SM and PM took place) the nn genotype had significantly lower glycogen and higher lactate levels in the SM muscle. In the PM muscle, both the Nn and nn genotypes had significantly lower glycogen levels. Very high lactate levels were observed in the PM muscle of all genotypes; since the PM muscle is highly oxidative, it appears to have almost completely metabolized stored glycogen and reached a near rigor state by the time sampling occurred. Es&n-Gustavsson et al. (1992) also reported lower glycogen and higher lactate levels in the longissimus muscle, when samples were collected immediately following exsanguination. Differences in the meat quality traits among the halothane genotypas (Table 5) are similar to those reported previously in the literature (Murray et al., 1989; Lundstrom et al., 1989; De Smet et al., 1993; Cheah et al., 1995; Minelli et al., 1995). In the SM, nn pigs had a significantly lower pHd5 and soluble protein and significantly higher L’ (paler) and shear (tougher) values compared with NN pigs. In the PM, nn pigs also had significantly TABLE 4 Genotype Means (SE) for Metabolite Concentrations and Muscle Fibre Type Areas in the Semimembranosus and Psoas major Muscles Semimembranosus NN Metabolites (mM g-r) Glycogen Lactate Glucidic potential Buffering capacityC Fibre areas? (wm) so FOG FG G

39.0b (3.40) 26.9“ (4.34) 53.7 (2.69) 83.1” (1.22) 2244ab (182) 2430 (198) 5508 (363) 8730 (1209)

Nn 3l.lb (3.60) 37.4” (4.59) 51.8 (2.84) 85.2”b (1.29) 19500 (196) 2470 (214) 4894 (392) 6918 (855)

Psoas major nn

10.0” (3.54) 66.3b (4.52) 46.9 (2.80) 88.6b (1.22) 2697b (214) 2936 (198) 6017 (363) 8525 (718)

NN

12.26 (1.80) 61.3 (4.36) 46.8 (2.41) 85.4 (1.95) 1015a (146) 1137” (151) 2522 (356) 3814” (1069)

Nn

62.3 (4.94) 39.7 (2.73) 82.2 (2.21) 1428ab (144) 1467ab (148) 3056 (349) 3659” (497)

abMeans within a muscle which are followed by different superscripts are significantly (p 5 0.05). CBuffering capacity is expressed in pmol HCl per unit change in pH. “SO, slow oxidative; FOG, fast, oxidative glycolytic; FG, fast, glycolytic; G, giant.

nn

72.7 (4.36) 45.9 (2.41) 79.5 (1.95) 1615b (151) 1823b (155) 3138 (367) 57456 (577) different

293

PST and stress susceptibility TABLE 5

Genotype Means for Quality Traits in the Semimembranosus and Psoas major Muscles Semimembranosus NN

Nn

nn

Psoas major SE

NN

Nn

nn

SE

-

Quality Traits ~H45 Temp4,

PH,I, CIE L* Hue angle Chroma Drip Loss, mg g-l Sheard Moisture, mg g-r Soluble Protein, mg g-’

6.32b 6.14”b 5.57” 40.3 39.6 40.7 5.45 5.40 5.45 51.2” 52.2‘= 56.4b 23.4” 26.1b 30.0’ 13.4 12.9 14.0 37.7 43.3 47.0 7.83“ 8.69b 9.36b 743 738 743 2006 1956 155”

5.51a 0.072 5.756 5.69”b 37.2 0.30 36.5 35.9 5.63b 0.018 5.49” 5.50” 49.3 0.83 47.4 47.7 21.7 0.81 19.6 20.8 20.5 0.38 20.2 20.3 25.8 3.20 17.5 23.5 3.66 0.288 3.52 3.31 752’ 1.8 749”b 746” 149” 4.5 1686 166b

0.068 0.47 0.033 0.85 0.95 0.56 3.54 0.160 1.6 5.8

U-cMeans within a muscle which are followed by different superscripts are significantly different (p < 0.05). dFor the SM muscle, Warner-Bratzler shears in kg; for the PM muscle, Kramer-Press-Ground compressions in kg/g.

lower pH45 and soluble protein and numerically lower L* and shear values. Drip losses also tended to be higher in both muscles in the nn compared with the NN genotype. In general the heterozygotes (Nn) were numerically intermediate for most of the quality traits measured. These differences in quality traits are commonly associated with PSE meat, however, as discussed previously, the reason for higher shear values in PSE meat is presently unknown (Aalhus et al., 1995).

CONCLUSION PST did not cause an increase in the proportion of G fibres or have an interactive effect with the halothane genotype. Overall, the effects of PST appear to be muscle and gender specific, which may be due to differences in maturity and rates of growth at the time of PST administration. The oxidative PM muscle of gilts showed the greatest response to PST with a 65-70% increase in fibre area in FOG and FG fibre. These changes in fibre type were manifest in minor shifts in meat quality traits (paler colour, increased drip, higher shear values). Thus, the administration of PST (timing, dosage and protein requirements in the feed) may need to be tailored to suit different genders and breeds to achieve maximal responses.

ACKNOWLEDGEMENTS The financial assistance of the former Pitman-Moore Company and the Alberta Agriculture Research Institute for partial funding is gratefully acknowledged. The authors also wish to thank Laverne Holt-Klimec, the staff at the Swine Unit and the staff at the Meat Centre for their diligent collection of live animal, slaughter and meat quality data. The skilled technical assistance of Madhu Badoni is also appreciated.

294

J. L. Aalhus et al.

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