Effect of breed on the muscle glycogen content and dark cutting incidence in stressed young bulls

Meat Science, Vol. 43, No. 1, 31-42, 1996 Copyright 0 1996 Else&r Science Ltd Printed in Great Britain. All rights reserved 0309-1740/96/U 5.00 + .OO ELSEVIER

0309-1740(95)00053-4

Effect of Breed on the Muscle Glycogen Content and Dark Cutting Incidence in Stressed Young Bulls M. C. Sanz,a M. T. Verde,a T. Siez” & C. Saiiudob uDpto de Patologia Animal, Facultad de Veterinania, bDpto de Producih Animal y Ciencia de 10s Alimentos, 500 13 Zaragoza, (Received

3 July 1995; revised version

Miguel Servet 177, 50013 Zaragoza, Spain Facultad de Veterinaria, Miguel Servet, 177, Spain

received 4 October

199.5; accepted

7 October

1995)

ABSTRACT Observations have shown relevant dtferences in the behaviour of Brown Swiss bulls and Pirenaico bulls. Because temperament is involved in the development of dark cutting beef (DC), the aim of this study was to investigate the influence of breed on muscle glycogen content and on the incidence of DC condition. Twenty-four Brown Swiss bulls and 24 Pirenaico bulls were used. The animals were divided into a stressed group (S) and a control group (C). In group S, bulls were mixed with unfamiliar animals overnight before slaughter. In group C, bulls were slaughtered immediately after arrival at the abattoir. The results show that the glycogen concentrations in m. longissimus dorsi and m. sternomandibularis from unstressed animals were similar in both the Brown Swiss and the Pirenaico breeds. The muscle glycogen concentration was depleted in all stressed bulls, nevertheless some low concentrations were insuficient to adversely affect the meat ultimate pH value. Finally, there was no infiuence of breed on the incidence of the dark cutting condition. Copyright 0 1996 Elsevier Science Ltd

INTRODUCTION Dark cutting beef is a meat quality problem which causes significant economic losses in the beef industry in many countries (Tarrant, 1981). The meat has a dark colour, a firm consistency, a sticky surface, and is more prone to bacterial spoilage. Therefore, it is discriminated against by consumers. The dark cutting condition (DC) in beef is a direct consequence of a reduced muscle glycogen concentration at slaughter. The loss of glycogen reserves occurs during the preslaughter period when the animals are exposed to various stressors, and can often be prevented by careful handling of animals from the time they leave the farm until they are slaughtered (Hedrick, 198 1). The frequency of DC beef can be influenced by factors such as animal category, nutritional status, transportation distance, season of year, mixing of unfamiliar cattle, lairage time, genetic predisposition, etc. Some of these factors have been studied in depth, but there is a lack of information concerning others, such as the effect of breed on the incidence of dark cutting in beef. 37

38

M. C. Sanz et al.

The aim of this study was to examine the glycogen muscle content at slaughter of unstressed and stressed animals in two different cattle breeds and to investigate the effect of breed on the incidence of dark cutting meat.

MATERIALS

AND METHODS

The animals used in the experiment were 24 Brown Swiss bulls and 24 Pirenaico bulls, 18 months old and weighing 460 kg. They were fed on concentrate supplemented forage diets. The animals were divided into two groups, a stressed group (group S) with 36 bulls (breeds in equal numbers) and a control group (group C) with 12 bulls. Animals in group S were transported to the slaughterhouse in mixed groups of animals which had been reared separately. The distance travelled was 10 km and the transport time was 10 min approximately. At the abattoir, the animals (in the new groups) were kept overnight in pens and had access to water but not food. They were slaughtered the next morning, 18 hr after arrival. Animals in group C were transported to the slaughterhouse in the original groups they had been reared. The distance travelled and the vehicle used were the same as that for group S but the animals were slaughtered immediately after arrival. Animals of both groups S and C were slaughtered in the same commercial abattoir by a process that involved stunning using a captive bolt, suspension by a hind leg, and exsanguination. The animals were slaughtered between the months of March and May. Samples were taken from the m. longissimus dorsi and m. sternomandibularis within 20 min of slaughter and frozen in liquid nitrogen pending analysis for glycogen content. Muscle glycogen was determined using an enzymatic method (Bermeyer and Bernt, 1974). Samples were homogenized in ice-cold percloric acid. After centrifugation, free and total glucose were determined in separate aliquots of supernatant fraction. The aliquot for total glucose was incubated with amyloglucosidase from Aspergillus niger (2 hr at 40°C) to degrade glycogen to glucosyl units. The difference between total glucose and free glucose was considered to be the glucose derived from glycogen and was expressed as pmol of glucose/g of tissue. The ultimate pH value (pH,) was measured in the m. longissimus dorsi (8th/9th rib) on the left side of each carcass 24 hr after slaughter with an electronic pH meter (Jenway; model 3060). The m. longissimus dorsi has been found to be the best indicator of high pH, in the musculature of the carcass. Dark cutting (DC) carcasses were classified as those with pH26. Chi-square test was carried out to compare qualitative variables: breed and type of meat. Differences between the means were assessed for statistical significance using an unpaired Student t-test. The results are presented as means & SE. RESULTS In group S, the pH, values varied between 5.17 and 7.07 (Fig. 1). Seventeen out of 36 animals produced dark cutting carcasses (47.2%). If we consider the two breeds separately, lo/18 bulls (55.6%) produced dark cutting meat in the Brown Swiss breed and 7/18 bulls (38.9%) produced the same in the Pirenaico breed (Table 1). There were no significant differences between the incidence of dark cutting in Brown Swiss and the Pirenaico breed (Chi-square: 0.446; p=O.50). In group C, the pH, values varied between 5.35 and 5.60 (Fig. 2). None of these animals had a pH, higher than 6.00.

Effect of breed on the muscle glycogen content

39

The glycogen concentration was higher in m. longissimus dorsi than in m. sternomandibularis from unstressed animals, but no breed differences were found in glycogen content in both muscles (Table 2). In group S, the muscle glycogen content of normal and DC bulls are shown in Table 3. All animals of group S, DC bulls as well as normal bulls,

5.00

5.25

1h

5.50

5.75

6.00

Ultimate

Fig. 1. Ultimate

Number

6.25

of Animals Carcasses

I,

7. IO

of the stressed

7.25

group (group S).

TABLE 1 which Showed Normal (pH < 6) and Dark-Cutting in the Stressed Group (Group S) n

pH<6

36 18 18

Total (Brown Swiss + Pirenaico) Brown Swiss Pirenaico Chi-square

6.75

pH

pH values found in bull carcasses

and Percentage

6.50

PH>6

19 (52,8%) 8 (44.4%) 11 (61.1%)

17 (47,2%) 10 (55.6%) 7 (38.9%)

= 0.446; p = 0.50.

8 7 ~1 6 7 ‘2E al

5

%

4

fii n

3

i

2

E

1 0 5.00

5.25

5.50

I. .

5.75

6.00

Ultimate

Fig. 2. Ultimate

c

6.25

6.50

6.75

7.00

7.25

pH

pH values found in bull carcasses

(pH>6)

of the control

group (group C).

40

M. C. Sunz et al. TABLE 2

Muscle Glycogen Content (pmol/g) in Brown Swiss and Pirenaico Bulls of the Control Group (Group C) Brown Swiss (n = 6)

Pirenaico (n = 6)

P

8 1.48 f 4.22 48.42 f 4.02

77.14h4.57 47.16 f 1.94

> 0.05 > 0.05

M. longissimus dorsi M. sternomandibularis

TABLE 3

(pmol/g) in Normal (pH < 6) and Dark-Cutting Stressed Group (Group S)

Muscle Glycogen Content

Brown Swiss pH
LD SM

Bulls of the

Pirenaico Pm6

50.71 f 3.84 28.27 f 2.82

(pH16)

14.82* 5.37”’ 13.73 f 2.93”

pH
55.91 f 6.35 39.99 f 2.45

Pm6

20.78 f 3.61”’ 29.0853159’

LD, m. longissimus dorsi; SM, m. sternomandibularis.

l,p
“,p
***,p<0.001.

showed lower glycogen concentrations than the animals from group C. The two muscles analysed showed significantly lower glycogen values in DC than in normal bulls, but the m. longissimus dorsi had a greater glycogen depletion.

DISCUSSION The two breeds included in this study are present in some areas of the Pyrenees mountains. Several observations made by farmers and researchers have shown that the Pirenaico breed is more nervous and more difficult to handle than the Brown Swiss breed. Because the development of dark cutting beef is associated with an excitable temperament (Tarrant, 1981), these findings would suggest that the incidence of dark cutting meat would be higher in the Pirenaico bulls. Selection of breeding animals which have no related incidences of dark cutting, and especially breeds which have a temperament not conducive to ready excitability should be considered as a preventive measure. However, in the present study, the incidence of dark cutting in Pirenaico bulls was not significantly different from the incidence of dark cutting in Brown Swiss bulls. There are few studies concerning the effect of breed on the incidence of dark cutting in beef. In general, dairy cattle seem to have a higher incidence of dark cutting meat (Morisse et al., 1984, 1985). Liboriussen (1982) reported that the breed differences with respect to changes in pH postmortem are few. The muscle glycogen concentration from control animals was similar in both Brown Swiss and Pirenaico breeds (Table 2). This result confirms the finding that there was no difference in the incidence of dark cutting between the breeds. In group C, the mean glycogen concentration in m. longissimus dorsi was similar to the value reported by other authors (80 pmol/g) for resting (Tarrant, 1989) or unstressed cattle (Kenny and Tarrant, 1988).

Eflect of breed on the muscle glycogen content

41

Therefore, the short haul road transport of this experiment had no effect on the glycogen muscle content, and, therefore, on the pH, of the carcasses. Transport distance has sometimes been claimed to increase the frequency of dark cutting by gradually reducing the glycogen reserves by fatigue, but this only has been reported in long haul transport (Tarrant et al., 1992) whereas short journeys do not affect the ultimate pH in cattle (Tarrant, 1989). The glycogen concentration in the m. sternomandibularis from control bulls was similar in the Brown Swiss and Pirenaico breed, although it was lower than the glycogen concentration in the m. longissimus dorsi. An explanation could be that, with rare exceptions, the m. sternomandibularis has a relatively high occurrence of SO fibres and none or few FG fibres (SO = slow, oxidative, FG = fast, glycolytic) (Young and Bass, 1984; Young and Foote, 1984). It has been demonstrated that in unstressed bulls, the SO fibres show lower glycogen content than FG or FOG fibres (FOG = fast, oxidative, glycolytic) (Lacourt and Tarrant, 1985). All animals slaughtered immediately after arrival at the abattoir produced carcasses with pH, < 6.00 in the m. longissimus dorsi, the mean value being 5.47 f 0.02. Since the only difference between groups S and C was mixing groups of unfamiliar animals overnight, we can conclude that the main cause of dark cutting was the social regrouping of bulls at the abattoir overnight. Simple handling changes are enough to prevent the dark cutting condition. All animals of group S, both normal and DC, showed lower glycogen concentration in their muscles than animals of group C. Despite the fact that pH, was not higher than 6.00 in normal bulls of group S, a considerable depletion of glycogen occurred, indicating a stress or emergency situation in these animals in group S. Therefore, the muscle glycogen content, more than the pH, could be considered a good index of pre-slaughter stress. In group S, the two muscles analysed showed significantly lower glycogen values in DC than in normal bulls. However, the m. longissimus dorsi showed a greater glycogen depletion than m. sternomandibularis. In commercial conditions, the highest pH, values are associated with the powerful muscles of the back and hind limbs, particularly the m. longissimus dorsi. These muscles may be selectively active before slaughter due to repetitive strenuous activity such as aggression or mounting, and so have a high consumption of glycogen (Talmant et al., 1986). Mixing penning is an intensive stressor with a high exercise component, but physical activity is probably accompanied by emotional arousal in response to a new and threatening situation. Adrenaline release causes a general glycogenolytic response throughout the skeletal musculature with glycogen depletion, even in muscles with a high proportion of SO fibres (Lacourt and Tarrant, 1985). Because of this fact, the glycogen depletion observed in the m. sternomandibularis suggests that, in this study, the animals subject to mixing not only experienced physical stress but also emotional stress. The results of the present study indicate that the m. longissimus dorsi and m. sternomandibularis glycogen concentration are similar in both Brown Swiss and Pirenaico breeds and that in spite of the apparent difference in temperament of these breeds, there is no influence on the incidence of dark cutting. The main cause of dark cutting was due to physical and emotional stress of mixing unfamiliar bulls overnight. REFERENCES Bermeyer, H. U. and Bernt. E. (1974). In: Methods of Enzymatic Analysis, ed. H. U. Bermeyer. Academic Press, London, Vol. 3, p. 1127. Hedrick, H. B. (1981). In: The Problem of Dark-cutting Beef, eds D. E. Hood and P. V. Tarrant. Martinus Nijhoff, The Hague, p. 213.

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hf. C. Sunz et al.

Kenny, F. J. and Tarrant, P. V. (1988). Meat Sci., 22, 21. Lacourt, A. and Tarrant, P. V. (1985). Meat Sci., 15, 85. Liboriussen, L. T. (1982). Curr. Top. Vet. Med. Anim. Sci., 21, 82. Morisse, J. P., Cotte, J. P. and Huonnic, D. (1985). Revue Technologique des Industries de la Vi&de et des Den&es d’origine Animale, 210, 13.

Morisse, J. P., L’Hospitalier,

R., Cotte, J. P. and Huonnic,

D. (1984). Revue Technologique

des

industries de la Viande et des Den&es d’origine Animale, 200, 10.

Talmant, A., Monin, G. Briand, M., Dadet, M. and Briand, Y. (1986). Meat Sci., 18, 23. Tarrant, P. V. (1981). In: The Problem of Dark-cutting BeeL eds D. E. Hood, and P. V. Tarrant. Martinus Nijhoff, The Hague, p. 3. Tarrant, P. V. (1989). Irish .I. Food Sci. Technol., 13, 1. Tarrant, P. V., Kenny, F. J., Harrington, D. and Murphy, M. (1992). Livestock Prod. Sci., 30, 223. Young, 0. A. and Bass, J. J. (1984). Meat Sci., 11, 139. Young, 0. A. and Foote, D. M. (1984). Meat Sci., 11, 159.