Effect of exercise and pre-slaughter stress on pork muscle characteristics

Meat Science 26 (1989) 121-129

Effect of Exercise and Pre-slaughter Stress on Pork Muscle Characteristics* P. K. Lewis, Jr, L. Y. Rakes, C. J. Brown & P. R. Noland Animal and Poultry Sciences Department, University of Arkansas, Fayetteville, Arkansas 72701, USA (Received 12 October 1988; revised version received 16 February 1989; accepted 5 March 1989)

ABSTRACT The effects of exercise, stress and chill temperature on pork muscle characteristics were studied in a 3 × 2 × 2 factorial experiment in which treatments were assigned to blocks made up of six pigs of the same sex from the same litter. Pigs were fed a corn-soybean meal diet with the two littermate pigs on each treatment f e d together. Treatments were (1) a control group receiving no exercise and fed in an 8 m z pen; (2) a treatment group fed in an 8 m z pen and driven 1.6km/dayfor 100 days prior to slaughter; and (3) a treatment group fed in pens with 40 m 2 floor space with feeders placed 5 m from their waterers. When the animals averaged approximately 105 kg in weight, one animal from each pair treated alike was subjected to standardized stress. After slaughter, one side was chilled at 2-3°C and the other at 13-15°C for 24h. Both sides were then chilled at 2-3°C for an additional 24h. Exercise did not affect average daily gain ( ADG ), feed efficiency, yield o f total wholesale cuts, muscle pH, protein solubility, fiber diameter and sarcomere length o f the Longissimus dorsi ( L D ) and Quadriceps femoris ( QF) muscles or the tenderness of the QF muscle. Exercise decreased backfat thickness and the subjective tenderness of the L D muscle. The effects of stress on the characteristics evaluated were consistent with those that have been previously reported. Chilling temperature and interactions involving chilling temperature did not affect any o f the characteristics studied. No exercise × stress interactions were observed. Protein solubility values indicated that pale, soft exudative ( P S E ) muscle was not a factor in any o f the treatments. It was concluded that exercise will produce leaner carcasses but less tender muscle and that exercise will not counteract the effects of pre-slaughter stress. * Published with the approval of the Director of the Arkansas Agricultural Experiment Station. 121 Meat Science 0309-1740/89/$03.50 © 1989 Elsevier Science Publishers Ltd, England. Printed in Great Britain

122

P . K . Lewis et al.

INTRODUCTION Previous research concerning the effects of 'training' exercise on certain carcass and muscle characteristics is inconclusive. 'Training' exercise refers to the amount of exercise that will cause muscle hypertrophy but not muscle exhaustion. This type of exercise increases muscle tenderness but causes no change in the average daily gain (ADG), feed efficiency, backfat thickness, loin eye area, muscle tenderness or percentage of wholesale cuts in the carcass (Skjervold et al., 1963; Hawrysh et al., 1974; Weiss et al., 1975; Fitts et al., 1976; Petrov & Zakhariev, 1982). Lewis et al. (1977) indicated that stress increases the muscle pH and tenderness if the muscle ultimate pH is above 6.2. Locker and Hagyard (1963) reported that beef muscle would exhibit cold-shortening if the muscle temperature was below 14°C with the onset of rigor. The objectives of this experiment were to determine the effect of 'training' exercise on live performance and the effect of 'training' exercise, preslaughter stress and chilling temperature on carcass characteristics, muscle characteristics and muscle tenderness of cooked pork. MATERIALS A N D METHODS Nine litters with six pigs of the same sex were assigned to three treatments of two animals each. All pigs were fed a corn-soybean meal diet. The control consisted of a pair of animals from each of the nine litters fed in an 8 m 2 pen with no exercise; a second treatment consisted of an exercised pair of animals from each litter fed in a pen containing 8 m 2 of floor space; and the third treatment consisted of a pair of animals from each litter fed in a pen containing 40 m 2 of floor space. Each 'training' exercise animal in treatment two was walked 1.6 km for 100 days prior to slaughter. In the third treatment the feeders were approximately 5 m from the waterers. When the animals in each pen averaged approximately 105 kg live weight per pig, one animal in each pen was subjected to 6 h of stress as described by Lewis et al. (1967). The animals were slaughtered, and one half of each carcass was chilled at 2-3°C and the other half-carcass at 13-15°C for the first 24h. Both sides were chilled for an additional 24 h at 2-3°C. Carcass characteristics were obtained (Am. Meat Sci. Assn., 1967) and samples of the L o n g i s s i m u s dorsi (LD) and Q u a d r i c e p s f e m o r i s (QF) muscles were then removed from the carcass and cooked as described by Lewis et al. (1977). Warner-Bratzler shear force values, panel tenderness, fiber diameter, sarcomere length, moisture and fat were obtained as described by Lewis et al. (1967). The pH of the raw samples was determined 48h after slaughter as described by Lewis et al. (1987). Protein solubility (Hart, 1962) was used to

Effect of exercise and pre-slaughter stress on pork muscle

123

evaluate the incidence of pale, soft exudative (PSE). Dry, firm, dark (DFD) muscle was classified as described by Fabiansson et al. (1984) by the 48 h pH. The statistical analysis used for the A D G and feed efficiency was based on pen averages. A randomized block single factor analysis of variance model that included a term associated with a c o m m o n element, litter, exercise treatment and a term for the remaining variance was used (SAS Institute Inc., 1985). The statistical model for the other variables analyzed was a randomized block split-plot 3 x 2 factorial. This least squares model included a term associated with a c o m m o n element, litter, exercise treatment, stress, exercise x stress interaction; litter x exercise x stress interaction; chilling temperature, exercise x chilling temperature interaction, stress x chilling temperature interaction, exercise x stress x chilling temperature interaction and a term for the remaining variance. Error terms used to test the level of significance in this model were (1) exercise, stress or exercise x stress interaction--the litter x exercise x stress interaction, and (2) chilling temperature and the above interactions involving chilling temperature-- the term for the remaining variance (SAS Institute Inc., 1985). Differences between means, if significant by the analysis of variance, were determined by least significant differences calculated by the G L M procedure of SAS (SAS Institute, Inc., 1985).

RESULTS A N D DISCUSSION The chilling rate of the LD and QF muscles due to chilling at either 2-3°C or 13-15°C is presented in Table 1. As expected, the chilling room temperatures used produced different chilling rates. Stress caused an increase (LD 40.4 versus 41.0°C; QF--40.8 versus 41-3°C) in the internal temperature in both muscles 0-5 h after slaughter but had no effect at any of the other times evaluated. No differences in chilling temperature and the above interactions involving chilling temperature were noted for the various carcass or muscle characteristics studied. Therefore, these variables were removed from the statistical model, and the left and right sides were averaged. No PSE muscle, as indicated by protein solubility, was observed. No exercise × stress interactions were found. Table 2 indicates the effect of exercise treatments on the A D G and feed efficiency. Exercise did not affect A D G or feed efficiency. This agrees with reports of Weiss et al. (1975) and Skjervold et al. (1963). The effect of exercise and ante-mortem stress on the incidence of D F D muscle is shown in Table 3. Exercise did not affect either the incidence of D F D muscle or the pH of the LD and QF muscles (Table 4). Ante-mortem

P . K . Lew~ et al.

124

TABLE 1 Effect o f Chill T e m p e r a t u r e o n the Internal T e m p e r a t u r e o f the L D a n d Q F Muscles °

Hours after

Chill temperature

Standard error

bleeding

2_3oc

13_15oC

of the mean

L D Muscle 0"5 3 5 24

40.7 24.3 16"0 3.0

40.8 28"9*** 23'0*** 13.5"**

0.04 0.2 0.2 0.4

Q F Muscle 0"5 3 5 24

41.1 32.8 24.3 3.9

41.1 35.4*** 30.3*** 14.8"**

0.03 0.2 0.2 0.5

*** P < 0.001. a N = 54 for each chilling temperature.

TABLE 2 T h e Effect o f Exercise o n the Live P e r f o r m a n c e o f Swine °

Treatment

Control

Walked 1"6 km/day

Feederwaterer 5 m apart

Standard error of mean

A D G (kg/day) b Feed efficiency c

0"84 3.62

0"79 3"56

0.76 3.48

0'02 0.07

a Each observation a n average o f two animals. b N = 9 for each treatment. c N = 8 for each treatment.

TABLE 3 The Effect o f Exercise a n d Stress o n the Incidence o f D F D Muscle a

Exercise stress D FD classification b

LDmuscle QFmuscle

Control

Walked 1"6 km/day

Feeder-waterer 5 m apart

Control 1 2 3

Stressed 1 2 3

Control 1 2 3

Stressed 1 2 3

Control 1 2 3

Stressed 1 2 3

4 2

3 2

4 2

3 1

6 2

4 1

5 6

0 1

6 3

0 4

5 6

a N = 9 for each treatment. b Classification based o n F a b i a n s s o n et al. (1984).

0 1

5 3

1 5

3 6

0 1

5 5

0 3

125

Effect of exercise and pre-slaughter stress on pork muscle

TABLE 4 Effect of Exercise on Certain Characteristics of the LD and QF muscles° Treatment

Control

Walked 1.6 km/day

Feederwaterer 5 m apart

Standard error of mean

LD muscle: Muscle pH Cooking loss (%) Panel tendernessa Shear force (kg)c Protein solubility (OD)4 Moisture (%)e Fat (%)e Fiber diameter (/zm) Sarcomere length (/zm)

5-8 38'3 5-8* 0.8 0.90 72.2 3.8 66.5 1.68

5.8 38.1 5.Y 1.0 0.90 72.4 3.3 65.1 1-67

5-8 38"0 5.3~ 1.0 0.89 72.4 3-1 64-5 1.68

0"03 0.5 0.1 0.1 0.02 0.2 0.2 0-8 0.02

QF muscle: Muscle pH Cooking loss (%) Panel tendernessb Shear force (kg)c Protein solubility (OD)d Moisture (%)e Fat (%)e Fiber diameter (/zm)g Sarcomere length (/am)g

6.0 35.7 5.7 1.3 0-74 72.5 4.9 59.9 2-03

6'0 34.8 5.6 1-3 0"80 72-8 4.6 61.7 2.12

6"0 35-6 5.6 1.4 0.77 73.0r 4.21 61-7 1.98

0-05 0.6 0.1 0.1 0.03 0'3 0"3 1.1 0.04

" N = 18 for each treatment unless otherwise noted. b Panel scores ranged from a 1 which was very tough to a 9 which was very tender. c 1'3 cm core. d Optical density. e Fresh weight basis. fN=16. g N = 12 for each treatment. hi Means within a row with different superscript letters are different P < 0"05.

stress increased the pH of the LD and QF muscles (Table 6), therefore increasing the incidence of D F D muscle. Ante-mortem stress produced the following incidence of D F D muscle: one D F D LD muscle, 16 slightly-DFD LD muscles, 10 normal LD muscles, 12 D F D QF muscles, 11 slightly-DFD QF muscles and four normal QF muscles out of 27 animals. The 27 control (non-stressed) animals had no D F D LD muscles, 13 slightly-DFD LD muscles, 14 normal LD muscles, three D F D QF muscles, 18 slightly-DFD QF muscles and six normal QF muscles. The stress treatment may have caused the secretion of adrenalin from the adrenal medulla causing a depletion of muscle glycogen. Decreased muscle

126

P . K . Lewis et al.

glycogen would cause the ultimate muscle pH values to be higher. This is the explanation for D F D muscle appearing in stressed animals. There is no explanation for the decreased incidence of D F D muscle in this experiment when compared to experiments conducted and reported in the 1960s. The decreased incidence of D F D muscle due to 6 h of pre-slaughter stress agrees with a recent report (Lewis, et al., 1987). Table 4 presents the effect of exercise on certain characteristics of the LD and QF muscles. The LD muscle of control animals, as evidenced by panel tenderness scores, was more tender than the muscle from exercised animals. Shear force values were not different but followed the same trends as shown in the panel tenderness scores. Significantly, no other change due to exercise was observed. Weiss et al. (1975) and Hawrysh et al. (1974) indicated no differences in shear force of the LD muscle due to exercise but Petrov and Zakhariev (1982) indicated increased tenderness with exercise. Fat concentration and sarcomere length have been associated with tenderness (Lawrie, 1985). In the present study, no changes in the fat content TABLE 5 Effect of Exercise on Certain Pork Carcass Characteristics a Control

Slaughter weight (kg) Fill (%) Live shrink (%) Dressing (%)b Adrenal weight (g/kg x 100) Liver (%)c Fatback thickness (cm) Carcass length (cm) Angle on forearm (°) Total wholesale cuts (%) Loin eye area (cm 2)

Walked 1.6 kin~day

Feederwaterer 5 m apart

Standard error o f mean

104.7 6"3 2"5 78-3

106-4 6"5 3"0 78"3

103'8 6-4 2.8 77.7

4"1 1'4

4.1 1"3

4'2 1'3

0'1 0"03

3"5~

3"1e

3-1 ¢

0' 1

80.2 gh

0-4

79"3yg

80.6*

1-4 0"4 0"2 0"3

137"0

136'0

136-0

1"0

66-3 35'0

66.6 36'0

66.7 36"0

0-4 1"0

a N = 18 for each treatment. h Chill weight basis. c % of live weight. ae Means within a row with different superscript letters are different P < 0"05. Jg* Means within a row with different superscript letters are different P < 0-06.

Effect of exercise and pre-slaughter stress on pork muscle

127

or the sarcomere length were due to exercise. The decrease in tenderness with exercise may have been due to an increase in total collagen and/or a decrease in heat-soluble collagen of the LD muscle. The effect of exercise on certain other carcass characteristics is presented in Table 5. Exercise did not effect dressing percentage, fill, live shrink, adrenal weight, liver weight, total wholesale cut yield, loin eye area or the angle of the forearm but did decrease the backfat thickness. Increased length of the carcass due to exercise was noted (P < 0.06). This small increase in the carcass length was probably brought about because littermates of the same TABLE 6 Effect of Ante-mortem Stress on Certain Characteristics of the LD and Q F Muscles a

Treatment

Control

Stress

Standard error of the mean

L D muscle: Muscle pH Cooking loss (%) Panel tenderness b Shear force (kg) c Protein solubility (OD) d Moisture (%)e Fat (%)e Fiber diameter (/am) Sarcomere length (/am)

5.8 38'6 5-6 0"9 0"88 72.3 3-4 64-1 1-68

5'9** 37.7 5.4 1.1 0.92 72.4 3.4 66-6* 1.67

0-02 0.4 0-1 0' 1 0"02 0.1 0.2 0'7 0"02

Q F muscle Muscle pH Cooking loss (%) Panel tenderness b Shear force (kg) c Protein solubility (OD) d Moisture (%)e Fat (%)e Fiber diameter (/am) g Sarcomere length (/am) g

5"9 36"9 5"5 1.5 0"69 72"5f 4'61 59.9 2"09

6.2*** 33"8*** 5"8** 1.1"* 0.85*** 73"1" 4"5 62-3 2-00

0"04 0-5 0"1 0.1 0.03 0"2 0"3 0.9 0'04

P < 0 ' 0 6 ; * P <0"05; ** P < 0"01; *** P < 0"001. " N = 27 for each treatment unless otherwise noted. b Panel scores ranged from a 9 which was very tender to a 1 which was very tough. c 1"3 cm core. d Optical density. e Fresh weight basis. I N=25. g N = 18 for each treatment.

128

P . K . Lewis et ai.

sex were used in each replication in this experiment. This increase would not have been significant if littermates had not been used. Placing the feeder 5-m from the waterer did decrease the backfat thickness but not carcass length when compared to the control animals. Weiss et al. (1975) reported that exercise did not affect wholesale cut yield, carcass length, carcass backfat thickness or loin eye area. However, Skjervold et al. (1963) indicated that exercise decreased the weight of caudal fat. Table 6 indicates the effect ofante-mortem stress on certain characteristics of the LD and QF muscles. Ante-mortem stress increased the muscle pH of both of these raw muscles, the tenderness of QF muscle, the fiber diameter of the raw LD muscle, and the protein solubility and moisture (fresh basis) of the QF raw muscle. Ante-mortem stress decreased the cooking loss of the QF muscle. This treatment increased the moisture content of the QF raw muscles when expressed on a fresh basis. Lewis et aL (1963) reported that stress increased the moisture content of the QF muscle when expressed on a carbohydrate-free basis. Similar findings regarding the effects of the amount of stress applied on muscle tenderness were reported by Lewis et al. (1987). The reason that stress did not increase the tenderness of the LD muscle is the low incidence of D F D muscle in the stressed animals (Table 3). Increased TABLE 7

Effect of Ante-mortem Stress on Certain Pork Carcass Characteristics a Treatment

Slaughter weight (kg) Fill (%) Live shrink (%) Dressing (%)b Adrenal weight, (gm/kg x 100) Liver (%)b Fatback thickness (cm) Carcass length (cm) Angle on forearm (°) Total wholesale cuts (%) Loin eye area (cm 2) * P < 0-05. a N = 27 for each treatment. b Live weight (%).

Control

Stress

Standard error of the mean

104.3 6"3 2.8 78"2

105.6 6.5 2.7 78"0

4.0 1.3

4.3 1.4

0.1 0.02

3.2

3-3

0.1

79.9

80.1

0.3

138.0

135.0"

1"0

66.6 36"0

66.5 36"0

0-3 1"0

1.1 0.3 0"2 0"2

Effect of exercise and pre-slaughter stress on pork muscle

129

tenderness due to stress has been reported previously when a high incidence of D F D muscle was produced by stress (Lewis et al., 1977). The effect of ante-mortem stress on certain other carcass characteristics is presented in Table 7. This treatment did not effect dressing percentage, fill, live shrink, adrenal weight, liver weight, total wholesale cut yield or loin eye area. A n t e - m o r t e m stress decreased the angle of the forearm but did not affect the backfat thickness and carcass length. The decreased angle of the forearm did not affect the yield of total wholesale cuts. A n t e - m o r t e m stress decreased the yield of shoulder (17.8 versus 17.4%) when the angle of the forearm was held constant by the analysis of covariance. This type of statistical analysis showed no other effects of ante-mortem stress on the yield of loin, side or ham. Similar results concerning the yield of the wholesale cuts due to stress have been reported previously by Lewis et aL (1962). There were no exercise × stress interactions. This would indicate that 'training' exercise did not counteract the effects of pre-slaughter stress.

CONCLUSIONS It was concluded that exercise will produce leaner pork carcasses but with less tender muscle, and will not counteract the effects of pre-slaughter stress.

REFERENCES Am. Meat Sci. Assn. (1967). Recommended Guides for Carcass Evaluation and Contests. Am. Meat Sci. Assn., Chicago, IL. Fabiansson, S., Erichsen, I., Reuthersward, A. L. & Malmfors, G. (1984). Meat Sci., 10, 21. Fitts, R. H., Cassens, R. G. & Kauffman, R. G. (1976). J. Anim. Sci., 42, 854. Hart, P. C. (1962). Tijdschr. Diergeneesk., 86, 159. Hawrysh, Z. J., Murray, D. M. & Bowland, J. P. (1974). Can. J. Anim. Sci., 54, 191. Lawrie, R. A. (1985). Meat Science. Pergamon Press, New York. Lewis, P. K., Jr, Brown, C. J. & Heck, M. C. (1962). J. Anon. Sci., 21, 196. Lewis, P. K., Jr, Brown, C. J. & Heck, M. C. (1963). J. Food Sci., 28, 669. Lewis, P. K., Jr, Brown, C. J. & Heck, M. C. (1967). J. Anon. Sci., 26, 1276. Lewis, P. K., Jr, Campbell, K. R., Heck, M. C. & Brown, C. J. (1977). Ark. Agr. Exp. Sta. Bull., 824. Lewis, P. K., Jr, Rakes, L. Y., Brown, C. J. & Noland, P. R.(1987). Meat Sci., 21, 137. Locker, R. H. & Hagyard, C. J. (1963). J. Sci. Food and Agric., 14, 787. Petrov, J. & Zakhariev, Z. I. (1982). Zhivotnov'D. Nauki., 18(7), 11. SAS Institute Inc. (1985). S A S Users Guide: Statistics (1982 edn). SAS Institute Inc., Cary, NC. Skjervold, H., Standal, N. & Bruflot, R. (1963). J. Anon. Sci., 22, 458. Weiss, G. M., Peo, E. R., Mandigo, R. W. & Moser, B. D. (1975). J. Anon. Sci., 40, 457.