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Effects of Sarcocystis miescheriana infection on carcass weight and meat quality of halothane-tested fattening pigs
Veterinary Parasitology, 25 (1987) 19-31 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
19
Effects of Sarcocystis miescheriana Infection on Carcass Weight and Meat Quality of HalothaneTested Fattening Pigs A. DAUGSCHIES, M. ROMMEL and T. SCHNIEDER
Institute of Parasitology, School of Veterinary Medicine, B~nteweg 17, D-3000 Hannover 71 (F.R.G.)
M. HENNING and E. KALLWEIT
Federal Agricultural Research Centre ( FAL), Institute for Animal Husbandry and Animal Behaviour, D-3057 Neustadt 1/Mariensee (F.R.G.) (Accepted for publication 23 September 1986)
ABSTRACT Daugschies, A., Rommel, M., Schnieder, T., Henning, M. and Kallweit, E., 1987. Effects of Sarcocystis rniescheriana infection on carcass weight and meat quality of halothane-tested fattening pigs. Vet. Parasitol., 25: 19-31. Ten halothane-positive pigs ( Group A) and ten halothane-negative pigs (Group C ) were each infected per os by 50 000 sporocysts of Sarcocystis rniescheriana when they had reached a mean body weight of 36 kg. Twelve halothane-positive pigs (Group B ) and ten halothane-negative pigs (Group D) served as non-infected controls. Thirteen weeks p.i. (post infection), the pigs were slaughtered and the carcass weights and the number of cystozoites in several muscles were determined. In addition, 11 parameters of meat quality were measured in Musculus longissimus dorsi (M.l.d.) and Musculus semimembranosus (M.s.): pH and temperature 30 rain and 24 h p.m. (post mortem), electrical conductance 45 rain, 60 min and 24 h p.m., colour brightness (FOP) and rigor values 30 rain and 24 h p.m. Additionally, the AMP, ADP, ATP and lactate contents were determined in samples from the M.l.d. The mean carcass weights of the infected pigs (A: 79.9 _+6.9 kg; C: 76.3 _+11.6 kg) were lower than those of the pigs of the non-infected groups (B: 85.7 _+8.0 kg; D: 87.5 _+7.0 kg). The pH values at 24 h p.m. were significantly higher in the M.l.d. of infected pigs than in M.l.d. of non-infected pigs. Electrical conductance in the M.s. at 45 rain p.m. was significantly higher in the halothane-negative infected pigs, but at 24 h p.m., the mean values of electrical conductance in the M.s. of the pigs of both infected groups were significantly lower than in the control groups. FOP values at 30 rain p.m. were raised in the M.l.d. of the halothane-negative infected pigs, but at 24 h p.m., differences between infected and non-infected pigs could no longer be found. Mean rigor values were higher in the pigs of the infected groups at 24 h p.m., but the difference from the non-infected groups was not statistically significant. AMP was reduced only in the meat of halothane-positive infected pigs, while lactate was reduced in both infected groups. Using conventional methods for the determination of meat quality, the hypoth-
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© 1987 Elsevier Science Publishers B.V.
2O esis of impaired meat quality in Sarcocystis-infected pigs could not be confirmed. The meat quality parameters investigated were, in part, better in infected pigs than in non-infected controls.
INTRODUCTION
Sarcosporidia are common parasites of pigs. Boch et al. (1978) found Sarcocystis infections in 9.7% of 766 fattening pigs and in 35.5% of 409 sows slaughtered at South German abattoirs. As early as 1922, Creech had suggested that the sarcosporidia could impair the meat quality of pigs. Pigs dying from acute sarcocystosis were repeatedly found to have extremely oedematous muscles (Zielasko et al., 1981; Weber et al., 1983 ). Erber and Geisel (1979) reported that nine pigs experimentally infected with Sarcocystis miescheriana and slaughtered 69 days later were downgraded at meat inspection because of watery meat. Similar features were seen by Schnieder and Rommel (1983) in pigs slaughtered 40 days after infection. Bogush {1975) and Bogush and Pyshko (1976) found low glycogen contents and an increased content of free fatty acids in the meat of Sarcocystis-infected pigs. The aim of the present study was to obtain objective data on the influences of S. miescheriana infections on the quality of the meat, using established routine methods. MATERIALS AND METHODS
One week after weaning, all pigs were tested for stress susceptibility by means of the halothane test. A semi-closed narcotic system and a halothane concentration of 4% were used. The duration of the test was 5 rain. The intensity of the halothane reaction was estimated by the method of Eikelenboom et al. (1976). The pigs were kept in isolation units at 21 °C and received a commercial feed 1, to which water was added for better acceptance. The feed was offered twice daily, 8 h apart. The daily amount of feed was designed to simulate commercial fattening. Water was offered ad libitum. Three weeks after weaning, the pigs were divided into two halothane-positive and two halothane-negative groups with almost equal mean body weights. The pigs of one halothane-positive group (A, n = 10) and one halothane-negative group (C, n--10) were each infected by 50 000 sporocysts of S. miescheriana per os when they had reached a mean body weight of 36 kg. The halothane-positive pigs of Group B (n= 12 ) and the halothane-negative pigs of Group D ( n = 10) were non-infected controls. The pigs were fattened, and slaughtered at the age of 28 weeks (13 weeks p.i. ). Carcass weights were recorded and the numbers of cystozoites in tongue, oesophagus, heart, diaphragm, Musculus masseter, M. Iongissimus dorsi 1Gebr. Weiterer, D-3201 Algermissen.
21
(M.l.d.), M. triceps brachii, M. semimembranosus ( M.s. ) and M. gracilis were counted according to the method described by Schnieder and Rommel (1983). Temperature (Technoterm 73001 ) and pH (Knick Portamess 651 with Ingold electrode2) were measured in the M.l.d. and in the M.s. 30 rain and 24 h after slaughter. Electrical conductance ( W T W Conduktometer LF 1913) was determined in M.l.d. and M.s. 45 rain, 60 rain and 24 h p.m. Colour brightness was measured in M.l.d. and M.s. by the fibre optic probe (tbl FIBRES Ltd. 4) 45 min and 24 h p.m. The rigor was measured at 30 min p.m. in M.s. and at 24 h p.m. in M.l.d. and M.s. and was used as a value for consistence by applying the method described by Sybesma (1966). All measurements of meat quality were in accordance with the recommendations of the West German performance and progeny testing system for pigs. For biochemical investigations, samples of the M.l.d. were taken 30 min p.m. and immediately frozen in liquid nitrogen. During the subsequent 6 months, the amounts of adenosine monophosphate (AMP), adenosine diphosphate (ADP), adenosine triphosphate (ATP) and lactate were determined in these samples using photometrical test kits s. Analyses of variance were carried out on all data. Additionally, the meat quality data were corrected to take account of the carcass weights and checked for statistical significance by covariance analysis. With the exception of carcass weights, statistical comparisons were made only between groups with similar halothane sensitivity. RESULTS
The mean carcass weights (Fig. 1 ) of the infected pigs (A: 79.9 -+11.6 kg; C: 76.3 _+11.6 kg) were lower than those of the pigs of the non-infected groups (B: 85.7_+8.0 kg; D: 87.5_+7.0 kg). Because of the individual variabilityof carcass weights, statisticallysignificantdifferenceswere only found between the two halothane-negative Groups C and D (P<0.05). Since there was no influence of stressdispositionon carcass weights, we compared the weights of all infected pigs (n = 20) with those of all controls (n = 22 ). A highly significant difference (P<0.01) in weight between infected (78.1 _+9.4 kg) and noninfected (86.5 -+7.4 kg) pigs was found. All pigs of the infected groups had very large numbers of cystozoitesin their muscles (Table I). There were no differencesbetween the numbers and distributions of cystozoitesin the meat of the pigs of the two infected groups. In seven non-infected pigs,a few cystozoiteswere also detected in the oesophagus, ~Technoterm KG, Postfach 1140, D-7825 Lenzkirch. ~KNICK Elektronische Messgertite GmbH, Beucksstr. 22, D-1000 Berlin 37. sWissenschaftlich-technische Werkstiitten, D-8120 Weilheim. 4tbl FIBRES Ltd., Torbay Works, Hunslet Road, Leeds LS10 1AU, U.K. 5Boehringer-Mannheim GmbH, Biochemica, Standhofer Str. 116, D-6800 Mannheim 31.
22
diaphragm muscles, M. masseter or M. gracilis. A quantitative determination of the number of cystozoites in the control pigs was not possible because cystozoites were only found sporadically and were too few in number to count. The temperature of the meat 30 min p.m. was similar in infected (A: 37.9+0.7°C; C: 37.9+0.5°C) and non-infected pigs (B: 38.4+1.1°C; D: 37.9_+ 0.5°C). The pH values in the meat of the pigs (Figs. 2 and 3) of the kg I00
90¸
80"
70-
60-
50
GROUPA GROUPB H*, infected H*, controls
11
GROUPC GROUPD H-,infected H-, controls
Fig. 1. Carcass weight of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts of S. miescheriana. pH 7,0-
s,s-
0
L,
5,5-
30
30 in ~\\\\\'~1
5,0"
GROUPA H*, infected
GROUP B H*, controls
GROUP C H-, infected
,
GROUP D H-, controts
Fig. 2. p H L~ ]ongissimus dorsi o f haiothane-tested pigs 13 weeks after infection b y 50 000 sporo-
cysts of S, miescheriana.
23 TABLE I
Mean number of cystozoites per gram of muscle in pigs infected by 50 000 sporocysts of S. miescheriana Group A (halothane positive, infected)
Tongue
Hea~ Oesophagus
Diaphragm M.m~sseter M. semimemb.
M. triceps M. longissimus
M. gracilis
300156 139088 245225 236760 209850 233338 46788 121255 396863
Group C (halothane negative, infected )
-+s
Number of pigs positive/ No: examined
£
_+s
Number of pigs positive/ No. examined
405249 354800 435813 247333 203268 365399 81435 191468 671420
10/10 10/10 10/10 10/10 10/10 10/10 10/10 10/10 10/10
684273 63558 349890 512435 572381 178185 64325 137888 274675
1148884 90712 638382 872562 1105714 177354 78241 168829 445699
10/10 10/10 10/10 10/10 10/10 10/10 10/1O 10/10 10/10
Group B (haiothane positive, control)
Group D (halothane negative, control)
Number of pigs positive/ No. examined
Number of pigs positive/ No. examined
Tongue Oesophagus
-Few
0/12 3/12
---
Diaphragm M. masseter
Few Few
2/12 1/12
Few Few
M. M. M. M.
semimemb. triceps longissimus
----
gracflis
Few
0/12 0/12 0/12 1/12
-----
0/10 0/10 3/10 1/10 0/10 0/10 0/10 0/10
Groups A, B and C, D were quite similar at 30 min p.m. At 24 h p.m., the pH values in the M.l.d. of the infected groups ( A: 5.57 + 0.04; C: 5.58 + 0.07) were higher than those of the respective controls (B: 5.51 + 0.03; D: 5.52 ___0.05). The difference between the pH values in the M.l.d. of the pigs of the halothanepositive infected and halothane-positive non-infected groups is statistically significant ( P < 0.01 ). Electrical conductance in M.s. (Figs. 4 and 5 ) was significantly ( P < 0.01) increased in the meat of the pigs of Group C at 45 rain p.m. (5.20+0.71) and 60 min p.m. (4.80_+0.42) compared with Group D ( 3.80 _+0.69; 4.00 + 0.43). At 24 h p.m., the values of electrical conductance in M.l.d. and M.s. of the infected pigs (A: 7.00 + 3.80 and 5.90 _+2.12; C: 2.70 + 0.98 and 4.90 _+1.23) were remarkably low compared with those of the respective controls (B: 10.70 -+ 2.52 and 10.90 -+ 1.80; D: 7.60 _+2.63 and 8.50 + 3.21). With the exception of the values in the M.l.d. of the halothane-positive groups at 24 h p.m., all differences in electrical conductance are statistically significant
(P<0.01). At 45 min p.m., the FOP values (Figs. 6 and 7) in the M.l.d. of the infected
24 pH
Z0-
6,5-
6,0
5,5
5,o
GROUPA H*, infected
GROUP B H*, controts
GROUP C H', infected
GROUP D H-, cOntrols
Fig. 3. p H in semimembranosus of halothane-testedpigs 13 weeks afterinfectionby 50 000 sporocysts of S. miescheriana. ELECTRICAL CONDUCTANCE 13 12. 11, 10-
I
9.
I
8-
76I i
:1 O-
45m~ 60 ~ir 24h
GROUPA
H ~, infected
GROUPB H*, controls
GROUPC H', infected
GROUP D H-, controls
Fig. 4. Electrical conductance in longissimus dorsi of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts of S. miescheriana. halothane-negative pigs ( C: 118.8 + 3.52 ) were significantly higher than those in the M.l.d. of the controls (D: 112.5 + 4.55). Twenty-four hours after slaughter, there was no longer any difference in F O P values in the meat of infected and non-infected pigs.
25 ELECTRICAL CONDUCTANCE 13-
12-
I II
II109~
-R
I--
!/I
I
£ I
o
1in 60 ~in 24h
h
GROUPA H', infected
GROUP B H*, controls
GROUPC H-, infected
I GROUPD H", controls
Fig. 5. Electrical conductance in semimembranosus of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts ofS. miescheriana.
COLOURBRIGHTNESS IFOP 170. 160. 150.
1
140.
I
130-
f
120110100,
90i
1
1
1.5 nin~2~
E
GROUPA H*, infected
{.5min 24h GROUP B H~,controls
GROUPC H-, infected
2hl GROUPD H-, controts
Fig. 6. Colour brightness (FOP) in longissimus dorsi of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts of S. miescheriana.
26 COLOUR BRIGHTNESS (FOP) 170 160 150
r
140 130 120 110
4Smir I 24h L GROUPA H*, infected
145rain 2Z,h i
GROUP B H+, controls
GROUPC H-, infected
GROUP D H-, controls
Fig. 7. Colour brightness (FOP) in semimembranosus of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts of S. miescheriana. RIGOR 13 12 11
]
10 9 8
? 6
5 4 3 2 1
0
GROUP A H*, infected
GROUPB H+,controls
GROUP C H-,infected
GROUP D H-, controls
Fig. 8. Rigor in longissimus dorsi (24 h p.m. ) of halothane-tested pigs 13 weeks after infectionby 50 000 sporocysts of S. miescheriana.
27
RIGOR 13
I
,2 11
10 9 8
7 6
34 2.
1O-
3C
30 ~ q
GROUPA H*, infected
GROUP B H*, controls
GROUP C H-, infected
2/oh GROUPO H-, controls
Fig. 9. Rigor in s e m i m e m b r a n o s u s of h a l o t h a n e - t e s t e d pigs 13 weeks after infection b y 50 000 s p o r o c y s t s o f S. miescheriana. TABLE II
A M P , ADP, A T P and lactate contents 30 rain p.m. in Musculus longissimus dorsi of pigs infected by 50 000 sporocysts of S. miescheriana Group
AMP (#mol g- ~)
ADP (pmol g- i)
ATP (pmol g- ])
Lactate (pmol g- i)
A ( H + , infected) x +s
0.164 0.045
1.126 0.135
3.449 1.362
63.429 17.070
B ( H + , control) x _s
0.277 0.157
1.221 0.142
2.329 1.526
85.809 17.338
C ( H - , infected) x +s
0.135 0.081
1.038 0.205
4.525 1.344
47.614 16.512
D ( H - , control) x _s
0.123 0.087
1.108 0.177
4.583 1.731
68.486 25.909
A:B P<0.05
A:B P<0.01 C:D P<0.05
28 The rigor values (Figs. 8 and 9) at 30 min p.m. were not affected by the infection. However, the halothane-negative infected pigs of Group C had significantly ( P < 0.05 ) increased rigor values (10.90 + 0.88 ) in M.l.d. at 24 h p.m. compared with the respective controls (9.20 _+1.48). At 24 h p.m., the mean rigor values were generally higher in the pigs of the infected groups than in the pigs of the non-infected groups, but with the exception of the values documented above, there was no statistical significance in the differences. The AMP content of muscles was significantly reduced ( P < 0.05) only in the halothane-positive infected pigs (0.16 mol g-1_+0.05) as compared with the controls (0.28 mol g-l_+ 0.16). ADP and ATP values were not altered by the infection. The lactate contents of the meat of the infected pigs (A: 63.43 _+17.07/lmol g- 1; C: 47.61 + 16.51/~mol g- 1) were significantly lower ( P < 0 . 0 1 A:B and P < 0 . 0 5 C:D) than in the controls (B: 85.81 + 17.34/~mol g-1; D: 68.49 + 25.91/~mol g-1) (Table II). DISCUSSION All investigated muscles of the infected pigs contained very large numbers of cystozoites. A few cystozoites were also found in some samples of seven noninfected control pigs. This demonstrates that it is very difficult to avoid infections with sarcosporidia completely, even when great care is taken. Since it is unlikely that the presence of a very low level of infection in some of the control pigs had any influence on the data obtained, it was neglected when analysing the data. In general, statistical tests were carried out only between groups of similar stress disposition to exclude genetical effects. Halothane sensitivity had no distinct effect on carcass weights. On the other hand, statistical analysis of the effects of the sarcosporidia on carcass weights was hampered by considerable individual weight differences and by the relatively small number of pigs in each group. Therefore, when comparing the carcass weights, the above-mentioned rule was not followed and two larger groups of pigs were formed without considering halothane sensitivity. In view of the results of Erber and Geisel (1979) and Zielasko et al. (1981), a Sarcocystis-induced reduction of carcass weights was expected. It was confirmed that even mild infections reduce the fattening capacity of pigs (9.7%, P < 0.01 ). "Meat quality" can be defined as the sum of several different parameters, e.g., chemical ingredients, marbling, colour, tenderness, taste and smell. The parameters investigated in this study are only part of the various factors influencing the quality of meat. (Water-binding capacity and the parameters usually referring to "carcass quality", i.e., fat-meat ratio, etc., will be reported in a separate paper. ) Most problems with meat quality in modern fattening pigs are caused by accelerated postmortal anaerobic glycolysis in the muscles and are generally known as PSE-syndrome. Rapid anaerobic glycolysis results in
29
accumulation of lactate as an acid metabolite in the muscles. Because of the decrease ofpH, membranes become fragile and more permeable to electrolytes. At the same time, denaturation of sarcoplasmic proteins occurs and the proteins lose their ability to bind water. Subsequently, the pH value of the meat decreases and so does water-binding capacity, while electrical conductance increases (Fialik et al., 1984). The meat becomes pale, soft and exudative (PSEmeat), a condition which is particularly noticeable in loin (M.l.d.) and ham (M.s.). These changes have been described after experimental infections with S. miescheriana (Ether and Geisel, 1979; Zielasko et al., 1981: Schnieder and Rommel, 1983; Weber et al., 1983). Therefore, these meat quality parameters were measured. The results of our tests do not indicate an impaired meat quality in infected pigs. Immediately after slaughter, no Sarcocystis-induced decrease of pH or increase of electrical conductance was observed. The lactate content of the M.l.d. was reduced in infected pigs. These results are in contrast to those expected in the PSE-syndrome. The slightly increased electrical conductance in the M.s. of the halothane-negative infected pigs shortly after slaughter does not seem to be of importance, because 24 h after the first measurement, the electrical conductance was significantly reduced in the meat of infected pigs and at the same time the infected pigs had higher pH values than the controls. The increased FOP values 45 rain p.m. in the M.l.d. of the halothane-negative infected pigs, like the transient increase of electrical conductance, may be regarded as of little importance. A possible explanation for the observed effects of the Sarcocystis infection on the tested parameters could have been the reduced weight gain of the infected pigs. This possibility was investigated by means of a statistical analysis of covariance. All pH, temperature, electrical conductance, rigor and FOP data were corrected to take account of the mean carcass weights and subsequently compared by an analysis of variance. All statistically significant differences were calculated in this way. It can, therefore, be stated that impaired growth rates are not exclusively responsible for the better results of the infected pigs. There must be a direct effect of a chronic Sarcocystis infection on the metabolism in the muscle tissue. One can only speculate as to how the sarcosporidia influence the meat quality. Probably the sarcocysts and their host cells do not respond in the same way as non-infected muscle cells to the suspension of blood circulation after slaughter. Mature sarcocysts are infectious stages of the parasite which survive for at least 3 weeks in the meat after slaughter and probably do not react with an increased anaerobic glycolysis to the death of the host. On the other hand, host cells might be altered in their metabolic activities by the parasite (less glycogen, less mitochondria? ) and may not be able to metabolize glycogen as rapidly as non-parasitized cells. In addition, it is even possible that the non-parasitized muscle cells might be influenced by metabolites of the parasites. However, this seems to be unlikely, because
30 metabolism in mature sarcocysts is restricted to a minimal level. On the other hand, it is questionable whether a minority of parasitized muscle cells could affect the parameters of meat quality without the participation of their noninfected environment. Bogush (1975) and Bogush and Pyshko (1976) observed a decreased glycogen content in Sarcocystis-infected meat shortly after slaughter. Bogush and Pyshko (1976) stated that at the same time, glycogen catabolism is retarded in parasitized muscles. These results are consistent with our observations, but do not explain the mechanisms responsible for the decreased glycogen content. Erber and Geisel (1979) observed that meat of pigs infected by 50 000 sporocysts of S. miescheriana 69 days before slaughter was exudative. Schnieder and Rommel (1983) also saw oedematous muscles 40 days p.i. Our pigs were slaughtered 91 days p.i. The meat of the pigs studied by these authors was infected with immature cysts which still had a considerable metabolic activity, whereas the cysts in our pigs were 91 days old and mature. The young cysts may impair the meat quality by toxic metabolites, while mature cysts with drastically reduced metabolism may have totally different effects. The oedema of muscles during acute sarcocystosis ( Zielasko et al., 1981; Weber et al., 1983 ) has to be explained in a different way. Acute sarcocystosis is accompanied by a crisis of blood circulation followed by extravasation in all tissues, including the muscles. From the results reported in the literature and from our data, it can be concluded that the different developmental stages of Sarcocystis, such as schizonts, young cysts and mature cysts have different effects on the metabolism in muscle tissue. In our experiments, there was no hint of a PSE-syndrome in pigs containing mature cysts, quite the contrary, the relevant measurements gave slightly better results for the infected animals. The observations suggest that the metabolic activities in muscle tissues were slowed down post mortem in the infected animals compared with those of the controls. The mechanism by which sarcosporidial infections influence the metabolism in host tissues are unknown and have to be investigated in further studies, but it is clear that even mild infections with S. miescheriana lead to reduced carcass weights and reduced daily gains. ACKNOWLEDGEMENTS This study was supported by a research grant from the German Research Council (DFG). Special thanks are given to Ms. Martina Walter and Ms. Irmtraud Peters-Greim for excellent technical assistance during this study.
REFERENCES Boch, J., Mannewitz, M. and Erber, M., 1978. Sarkosporidien bei Schlachtschweinen in Siiddeutschland. Berl. Miinch. Tier'~rztl. Wochenschr., 91: 106-111.
31 Bogush, A.A., 1975. (Effect of Sarcocystis invasion on pork quality). Veterinariya (Moscow), No. 8:101-103 (in Russian). Bogush, A.A. and Pyshko, I.I., 1976. (Glycogen content of the muscles and liver of pigs infected with Sarcocystis). Tr. Beloruss. Nauchno-Issled. Inst. Eksp. Vet. (Veterinarnaya nauka ~proizvodstvu), 14:173-174 (in Russian). Creech, G.T., 1922. Sarcosporidiosis of swine, associated with advanced degenerative changes in the musculature. J. Am. Vet. Med. Assoc., 61: 383-392. Eikelenboom, G., Minkema, D. and van Eldig, P., 1976. The application of the halothane test. Differences in production characters between pigs qualified as reactors (MHS-susceptible) and non-reactors. Proc. 3rd Int. Conf. Prod. Dis. Farm Anita., Wageningen, The Netherlands, pp. 183-187. Erber, M. and Geisel, O., 1979. Untersuchungen zur Klinik und Pathologie der Sarcocystis suicanis-Infektion beim Schwein. Berl. Mtinch. Tieriirztl. Wochenschr., 92: 197-202. Fialik, E., Pftitzner, H. and Krause, E., 1984. Routinem~issige Erkennung von PSE-Muskulatur dutch einen elektrophysikalischen Schnelltest. Wiener Tier~ierztl. Monatsschr., 71: 66-70. Schnieder, T. and Rommel, M., 1983. Ausbildung und Dauer der Immunit~t gegen Sarcocystis miescheriana im Schwein bei kontinuierlicher Verabreichung kleiner Mengen yon Sporozysten. Berl. Miinch. Tier'drztl. Wochenschr., 96: 167-170. Sybesma, W., 1966. Die Messung des Unterschiedes im Auftreten des Rigor morris im Schinken. Fleischwirtschaft, 46: 637-639. Weber, M., Weyreter, H., O'Donoghue, P.J., Rommel, M. and Trautwein, G., 1983. Persistence of acquired immunity to Sarcocystis miescheriana infection in growing pigs. Vet. Parasitol., 13: 287-297. Zielasko, B., Petrich, J., Trautwein, G. and Rommel, M., 1981. Untersuchungen fiber pathologisch-anatomische Ver~nderungen und die Entwicklung der Immunit~it bei der Sarcocystis suicanis-Infektion. Berl. Miinch. Tier'drztl. Wochenschr., 94: 223-228.
19
Effects of Sarcocystis miescheriana Infection on Carcass Weight and Meat Quality of HalothaneTested Fattening Pigs A. DAUGSCHIES, M. ROMMEL and T. SCHNIEDER
Institute of Parasitology, School of Veterinary Medicine, B~nteweg 17, D-3000 Hannover 71 (F.R.G.)
M. HENNING and E. KALLWEIT
Federal Agricultural Research Centre ( FAL), Institute for Animal Husbandry and Animal Behaviour, D-3057 Neustadt 1/Mariensee (F.R.G.) (Accepted for publication 23 September 1986)
ABSTRACT Daugschies, A., Rommel, M., Schnieder, T., Henning, M. and Kallweit, E., 1987. Effects of Sarcocystis rniescheriana infection on carcass weight and meat quality of halothane-tested fattening pigs. Vet. Parasitol., 25: 19-31. Ten halothane-positive pigs ( Group A) and ten halothane-negative pigs (Group C ) were each infected per os by 50 000 sporocysts of Sarcocystis rniescheriana when they had reached a mean body weight of 36 kg. Twelve halothane-positive pigs (Group B ) and ten halothane-negative pigs (Group D) served as non-infected controls. Thirteen weeks p.i. (post infection), the pigs were slaughtered and the carcass weights and the number of cystozoites in several muscles were determined. In addition, 11 parameters of meat quality were measured in Musculus longissimus dorsi (M.l.d.) and Musculus semimembranosus (M.s.): pH and temperature 30 rain and 24 h p.m. (post mortem), electrical conductance 45 rain, 60 min and 24 h p.m., colour brightness (FOP) and rigor values 30 rain and 24 h p.m. Additionally, the AMP, ADP, ATP and lactate contents were determined in samples from the M.l.d. The mean carcass weights of the infected pigs (A: 79.9 _+6.9 kg; C: 76.3 _+11.6 kg) were lower than those of the pigs of the non-infected groups (B: 85.7 _+8.0 kg; D: 87.5 _+7.0 kg). The pH values at 24 h p.m. were significantly higher in the M.l.d. of infected pigs than in M.l.d. of non-infected pigs. Electrical conductance in the M.s. at 45 rain p.m. was significantly higher in the halothane-negative infected pigs, but at 24 h p.m., the mean values of electrical conductance in the M.s. of the pigs of both infected groups were significantly lower than in the control groups. FOP values at 30 rain p.m. were raised in the M.l.d. of the halothane-negative infected pigs, but at 24 h p.m., differences between infected and non-infected pigs could no longer be found. Mean rigor values were higher in the pigs of the infected groups at 24 h p.m., but the difference from the non-infected groups was not statistically significant. AMP was reduced only in the meat of halothane-positive infected pigs, while lactate was reduced in both infected groups. Using conventional methods for the determination of meat quality, the hypoth-
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© 1987 Elsevier Science Publishers B.V.
2O esis of impaired meat quality in Sarcocystis-infected pigs could not be confirmed. The meat quality parameters investigated were, in part, better in infected pigs than in non-infected controls.
INTRODUCTION
Sarcosporidia are common parasites of pigs. Boch et al. (1978) found Sarcocystis infections in 9.7% of 766 fattening pigs and in 35.5% of 409 sows slaughtered at South German abattoirs. As early as 1922, Creech had suggested that the sarcosporidia could impair the meat quality of pigs. Pigs dying from acute sarcocystosis were repeatedly found to have extremely oedematous muscles (Zielasko et al., 1981; Weber et al., 1983 ). Erber and Geisel (1979) reported that nine pigs experimentally infected with Sarcocystis miescheriana and slaughtered 69 days later were downgraded at meat inspection because of watery meat. Similar features were seen by Schnieder and Rommel (1983) in pigs slaughtered 40 days after infection. Bogush {1975) and Bogush and Pyshko (1976) found low glycogen contents and an increased content of free fatty acids in the meat of Sarcocystis-infected pigs. The aim of the present study was to obtain objective data on the influences of S. miescheriana infections on the quality of the meat, using established routine methods. MATERIALS AND METHODS
One week after weaning, all pigs were tested for stress susceptibility by means of the halothane test. A semi-closed narcotic system and a halothane concentration of 4% were used. The duration of the test was 5 rain. The intensity of the halothane reaction was estimated by the method of Eikelenboom et al. (1976). The pigs were kept in isolation units at 21 °C and received a commercial feed 1, to which water was added for better acceptance. The feed was offered twice daily, 8 h apart. The daily amount of feed was designed to simulate commercial fattening. Water was offered ad libitum. Three weeks after weaning, the pigs were divided into two halothane-positive and two halothane-negative groups with almost equal mean body weights. The pigs of one halothane-positive group (A, n = 10) and one halothane-negative group (C, n--10) were each infected by 50 000 sporocysts of S. miescheriana per os when they had reached a mean body weight of 36 kg. The halothane-positive pigs of Group B (n= 12 ) and the halothane-negative pigs of Group D ( n = 10) were non-infected controls. The pigs were fattened, and slaughtered at the age of 28 weeks (13 weeks p.i. ). Carcass weights were recorded and the numbers of cystozoites in tongue, oesophagus, heart, diaphragm, Musculus masseter, M. Iongissimus dorsi 1Gebr. Weiterer, D-3201 Algermissen.
21
(M.l.d.), M. triceps brachii, M. semimembranosus ( M.s. ) and M. gracilis were counted according to the method described by Schnieder and Rommel (1983). Temperature (Technoterm 73001 ) and pH (Knick Portamess 651 with Ingold electrode2) were measured in the M.l.d. and in the M.s. 30 rain and 24 h after slaughter. Electrical conductance ( W T W Conduktometer LF 1913) was determined in M.l.d. and M.s. 45 rain, 60 rain and 24 h p.m. Colour brightness was measured in M.l.d. and M.s. by the fibre optic probe (tbl FIBRES Ltd. 4) 45 min and 24 h p.m. The rigor was measured at 30 min p.m. in M.s. and at 24 h p.m. in M.l.d. and M.s. and was used as a value for consistence by applying the method described by Sybesma (1966). All measurements of meat quality were in accordance with the recommendations of the West German performance and progeny testing system for pigs. For biochemical investigations, samples of the M.l.d. were taken 30 min p.m. and immediately frozen in liquid nitrogen. During the subsequent 6 months, the amounts of adenosine monophosphate (AMP), adenosine diphosphate (ADP), adenosine triphosphate (ATP) and lactate were determined in these samples using photometrical test kits s. Analyses of variance were carried out on all data. Additionally, the meat quality data were corrected to take account of the carcass weights and checked for statistical significance by covariance analysis. With the exception of carcass weights, statistical comparisons were made only between groups with similar halothane sensitivity. RESULTS
The mean carcass weights (Fig. 1 ) of the infected pigs (A: 79.9 -+11.6 kg; C: 76.3 _+11.6 kg) were lower than those of the pigs of the non-infected groups (B: 85.7_+8.0 kg; D: 87.5_+7.0 kg). Because of the individual variabilityof carcass weights, statisticallysignificantdifferenceswere only found between the two halothane-negative Groups C and D (P<0.05). Since there was no influence of stressdispositionon carcass weights, we compared the weights of all infected pigs (n = 20) with those of all controls (n = 22 ). A highly significant difference (P<0.01) in weight between infected (78.1 _+9.4 kg) and noninfected (86.5 -+7.4 kg) pigs was found. All pigs of the infected groups had very large numbers of cystozoitesin their muscles (Table I). There were no differencesbetween the numbers and distributions of cystozoitesin the meat of the pigs of the two infected groups. In seven non-infected pigs,a few cystozoiteswere also detected in the oesophagus, ~Technoterm KG, Postfach 1140, D-7825 Lenzkirch. ~KNICK Elektronische Messgertite GmbH, Beucksstr. 22, D-1000 Berlin 37. sWissenschaftlich-technische Werkstiitten, D-8120 Weilheim. 4tbl FIBRES Ltd., Torbay Works, Hunslet Road, Leeds LS10 1AU, U.K. 5Boehringer-Mannheim GmbH, Biochemica, Standhofer Str. 116, D-6800 Mannheim 31.
22
diaphragm muscles, M. masseter or M. gracilis. A quantitative determination of the number of cystozoites in the control pigs was not possible because cystozoites were only found sporadically and were too few in number to count. The temperature of the meat 30 min p.m. was similar in infected (A: 37.9+0.7°C; C: 37.9+0.5°C) and non-infected pigs (B: 38.4+1.1°C; D: 37.9_+ 0.5°C). The pH values in the meat of the pigs (Figs. 2 and 3) of the kg I00
90¸
80"
70-
60-
50
GROUPA GROUPB H*, infected H*, controls
11
GROUPC GROUPD H-,infected H-, controls
Fig. 1. Carcass weight of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts of S. miescheriana. pH 7,0-
s,s-
0
L,
5,5-
30
30 in ~\\\\\'~1
5,0"
GROUPA H*, infected
GROUP B H*, controls
GROUP C H-, infected
,
GROUP D H-, controts
Fig. 2. p H L~ ]ongissimus dorsi o f haiothane-tested pigs 13 weeks after infection b y 50 000 sporo-
cysts of S, miescheriana.
23 TABLE I
Mean number of cystozoites per gram of muscle in pigs infected by 50 000 sporocysts of S. miescheriana Group A (halothane positive, infected)
Tongue
Hea~ Oesophagus
Diaphragm M.m~sseter M. semimemb.
M. triceps M. longissimus
M. gracilis
300156 139088 245225 236760 209850 233338 46788 121255 396863
Group C (halothane negative, infected )
-+s
Number of pigs positive/ No: examined
£
_+s
Number of pigs positive/ No. examined
405249 354800 435813 247333 203268 365399 81435 191468 671420
10/10 10/10 10/10 10/10 10/10 10/10 10/10 10/10 10/10
684273 63558 349890 512435 572381 178185 64325 137888 274675
1148884 90712 638382 872562 1105714 177354 78241 168829 445699
10/10 10/10 10/10 10/10 10/10 10/10 10/1O 10/10 10/10
Group B (haiothane positive, control)
Group D (halothane negative, control)
Number of pigs positive/ No. examined
Number of pigs positive/ No. examined
Tongue Oesophagus
-Few
0/12 3/12
---
Diaphragm M. masseter
Few Few
2/12 1/12
Few Few
M. M. M. M.
semimemb. triceps longissimus
----
gracflis
Few
0/12 0/12 0/12 1/12
-----
0/10 0/10 3/10 1/10 0/10 0/10 0/10 0/10
Groups A, B and C, D were quite similar at 30 min p.m. At 24 h p.m., the pH values in the M.l.d. of the infected groups ( A: 5.57 + 0.04; C: 5.58 + 0.07) were higher than those of the respective controls (B: 5.51 + 0.03; D: 5.52 ___0.05). The difference between the pH values in the M.l.d. of the pigs of the halothanepositive infected and halothane-positive non-infected groups is statistically significant ( P < 0.01 ). Electrical conductance in M.s. (Figs. 4 and 5 ) was significantly ( P < 0.01) increased in the meat of the pigs of Group C at 45 rain p.m. (5.20+0.71) and 60 min p.m. (4.80_+0.42) compared with Group D ( 3.80 _+0.69; 4.00 + 0.43). At 24 h p.m., the values of electrical conductance in M.l.d. and M.s. of the infected pigs (A: 7.00 + 3.80 and 5.90 _+2.12; C: 2.70 + 0.98 and 4.90 _+1.23) were remarkably low compared with those of the respective controls (B: 10.70 -+ 2.52 and 10.90 -+ 1.80; D: 7.60 _+2.63 and 8.50 + 3.21). With the exception of the values in the M.l.d. of the halothane-positive groups at 24 h p.m., all differences in electrical conductance are statistically significant
(P<0.01). At 45 min p.m., the FOP values (Figs. 6 and 7) in the M.l.d. of the infected
24 pH
Z0-
6,5-
6,0
5,5
5,o
GROUPA H*, infected
GROUP B H*, controts
GROUP C H', infected
GROUP D H-, cOntrols
Fig. 3. p H in semimembranosus of halothane-testedpigs 13 weeks afterinfectionby 50 000 sporocysts of S. miescheriana. ELECTRICAL CONDUCTANCE 13 12. 11, 10-
I
9.
I
8-
76I i
:1 O-
45m~ 60 ~ir 24h
GROUPA
H ~, infected
GROUPB H*, controls
GROUPC H', infected
GROUP D H-, controls
Fig. 4. Electrical conductance in longissimus dorsi of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts of S. miescheriana. halothane-negative pigs ( C: 118.8 + 3.52 ) were significantly higher than those in the M.l.d. of the controls (D: 112.5 + 4.55). Twenty-four hours after slaughter, there was no longer any difference in F O P values in the meat of infected and non-infected pigs.
25 ELECTRICAL CONDUCTANCE 13-
12-
I II
II109~
-R
I--
!/I
I
£ I
o
1in 60 ~in 24h
h
GROUPA H', infected
GROUP B H*, controls
GROUPC H-, infected
I GROUPD H", controls
Fig. 5. Electrical conductance in semimembranosus of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts ofS. miescheriana.
COLOURBRIGHTNESS IFOP 170. 160. 150.
1
140.
I
130-
f
120110100,
90i
1
1
1.5 nin~2~
E
GROUPA H*, infected
{.5min 24h GROUP B H~,controls
GROUPC H-, infected
2hl GROUPD H-, controts
Fig. 6. Colour brightness (FOP) in longissimus dorsi of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts of S. miescheriana.
26 COLOUR BRIGHTNESS (FOP) 170 160 150
r
140 130 120 110
4Smir I 24h L GROUPA H*, infected
145rain 2Z,h i
GROUP B H+, controls
GROUPC H-, infected
GROUP D H-, controls
Fig. 7. Colour brightness (FOP) in semimembranosus of halothane-tested pigs 13 weeks after infection by 50 000 sporocysts of S. miescheriana. RIGOR 13 12 11
]
10 9 8
? 6
5 4 3 2 1
0
GROUP A H*, infected
GROUPB H+,controls
GROUP C H-,infected
GROUP D H-, controls
Fig. 8. Rigor in longissimus dorsi (24 h p.m. ) of halothane-tested pigs 13 weeks after infectionby 50 000 sporocysts of S. miescheriana.
27
RIGOR 13
I
,2 11
10 9 8
7 6
34 2.
1O-
3C
30 ~ q
GROUPA H*, infected
GROUP B H*, controls
GROUP C H-, infected
2/oh GROUPO H-, controls
Fig. 9. Rigor in s e m i m e m b r a n o s u s of h a l o t h a n e - t e s t e d pigs 13 weeks after infection b y 50 000 s p o r o c y s t s o f S. miescheriana. TABLE II
A M P , ADP, A T P and lactate contents 30 rain p.m. in Musculus longissimus dorsi of pigs infected by 50 000 sporocysts of S. miescheriana Group
AMP (#mol g- ~)
ADP (pmol g- i)
ATP (pmol g- ])
Lactate (pmol g- i)
A ( H + , infected) x +s
0.164 0.045
1.126 0.135
3.449 1.362
63.429 17.070
B ( H + , control) x _s
0.277 0.157
1.221 0.142
2.329 1.526
85.809 17.338
C ( H - , infected) x +s
0.135 0.081
1.038 0.205
4.525 1.344
47.614 16.512
D ( H - , control) x _s
0.123 0.087
1.108 0.177
4.583 1.731
68.486 25.909
A:B P<0.05
A:B P<0.01 C:D P<0.05
28 The rigor values (Figs. 8 and 9) at 30 min p.m. were not affected by the infection. However, the halothane-negative infected pigs of Group C had significantly ( P < 0.05 ) increased rigor values (10.90 + 0.88 ) in M.l.d. at 24 h p.m. compared with the respective controls (9.20 _+1.48). At 24 h p.m., the mean rigor values were generally higher in the pigs of the infected groups than in the pigs of the non-infected groups, but with the exception of the values documented above, there was no statistical significance in the differences. The AMP content of muscles was significantly reduced ( P < 0.05) only in the halothane-positive infected pigs (0.16 mol g-1_+0.05) as compared with the controls (0.28 mol g-l_+ 0.16). ADP and ATP values were not altered by the infection. The lactate contents of the meat of the infected pigs (A: 63.43 _+17.07/lmol g- 1; C: 47.61 + 16.51/~mol g- 1) were significantly lower ( P < 0 . 0 1 A:B and P < 0 . 0 5 C:D) than in the controls (B: 85.81 + 17.34/~mol g-1; D: 68.49 + 25.91/~mol g-1) (Table II). DISCUSSION All investigated muscles of the infected pigs contained very large numbers of cystozoites. A few cystozoites were also found in some samples of seven noninfected control pigs. This demonstrates that it is very difficult to avoid infections with sarcosporidia completely, even when great care is taken. Since it is unlikely that the presence of a very low level of infection in some of the control pigs had any influence on the data obtained, it was neglected when analysing the data. In general, statistical tests were carried out only between groups of similar stress disposition to exclude genetical effects. Halothane sensitivity had no distinct effect on carcass weights. On the other hand, statistical analysis of the effects of the sarcosporidia on carcass weights was hampered by considerable individual weight differences and by the relatively small number of pigs in each group. Therefore, when comparing the carcass weights, the above-mentioned rule was not followed and two larger groups of pigs were formed without considering halothane sensitivity. In view of the results of Erber and Geisel (1979) and Zielasko et al. (1981), a Sarcocystis-induced reduction of carcass weights was expected. It was confirmed that even mild infections reduce the fattening capacity of pigs (9.7%, P < 0.01 ). "Meat quality" can be defined as the sum of several different parameters, e.g., chemical ingredients, marbling, colour, tenderness, taste and smell. The parameters investigated in this study are only part of the various factors influencing the quality of meat. (Water-binding capacity and the parameters usually referring to "carcass quality", i.e., fat-meat ratio, etc., will be reported in a separate paper. ) Most problems with meat quality in modern fattening pigs are caused by accelerated postmortal anaerobic glycolysis in the muscles and are generally known as PSE-syndrome. Rapid anaerobic glycolysis results in
29
accumulation of lactate as an acid metabolite in the muscles. Because of the decrease ofpH, membranes become fragile and more permeable to electrolytes. At the same time, denaturation of sarcoplasmic proteins occurs and the proteins lose their ability to bind water. Subsequently, the pH value of the meat decreases and so does water-binding capacity, while electrical conductance increases (Fialik et al., 1984). The meat becomes pale, soft and exudative (PSEmeat), a condition which is particularly noticeable in loin (M.l.d.) and ham (M.s.). These changes have been described after experimental infections with S. miescheriana (Ether and Geisel, 1979; Zielasko et al., 1981: Schnieder and Rommel, 1983; Weber et al., 1983). Therefore, these meat quality parameters were measured. The results of our tests do not indicate an impaired meat quality in infected pigs. Immediately after slaughter, no Sarcocystis-induced decrease of pH or increase of electrical conductance was observed. The lactate content of the M.l.d. was reduced in infected pigs. These results are in contrast to those expected in the PSE-syndrome. The slightly increased electrical conductance in the M.s. of the halothane-negative infected pigs shortly after slaughter does not seem to be of importance, because 24 h after the first measurement, the electrical conductance was significantly reduced in the meat of infected pigs and at the same time the infected pigs had higher pH values than the controls. The increased FOP values 45 rain p.m. in the M.l.d. of the halothane-negative infected pigs, like the transient increase of electrical conductance, may be regarded as of little importance. A possible explanation for the observed effects of the Sarcocystis infection on the tested parameters could have been the reduced weight gain of the infected pigs. This possibility was investigated by means of a statistical analysis of covariance. All pH, temperature, electrical conductance, rigor and FOP data were corrected to take account of the mean carcass weights and subsequently compared by an analysis of variance. All statistically significant differences were calculated in this way. It can, therefore, be stated that impaired growth rates are not exclusively responsible for the better results of the infected pigs. There must be a direct effect of a chronic Sarcocystis infection on the metabolism in the muscle tissue. One can only speculate as to how the sarcosporidia influence the meat quality. Probably the sarcocysts and their host cells do not respond in the same way as non-infected muscle cells to the suspension of blood circulation after slaughter. Mature sarcocysts are infectious stages of the parasite which survive for at least 3 weeks in the meat after slaughter and probably do not react with an increased anaerobic glycolysis to the death of the host. On the other hand, host cells might be altered in their metabolic activities by the parasite (less glycogen, less mitochondria? ) and may not be able to metabolize glycogen as rapidly as non-parasitized cells. In addition, it is even possible that the non-parasitized muscle cells might be influenced by metabolites of the parasites. However, this seems to be unlikely, because
30 metabolism in mature sarcocysts is restricted to a minimal level. On the other hand, it is questionable whether a minority of parasitized muscle cells could affect the parameters of meat quality without the participation of their noninfected environment. Bogush (1975) and Bogush and Pyshko (1976) observed a decreased glycogen content in Sarcocystis-infected meat shortly after slaughter. Bogush and Pyshko (1976) stated that at the same time, glycogen catabolism is retarded in parasitized muscles. These results are consistent with our observations, but do not explain the mechanisms responsible for the decreased glycogen content. Erber and Geisel (1979) observed that meat of pigs infected by 50 000 sporocysts of S. miescheriana 69 days before slaughter was exudative. Schnieder and Rommel (1983) also saw oedematous muscles 40 days p.i. Our pigs were slaughtered 91 days p.i. The meat of the pigs studied by these authors was infected with immature cysts which still had a considerable metabolic activity, whereas the cysts in our pigs were 91 days old and mature. The young cysts may impair the meat quality by toxic metabolites, while mature cysts with drastically reduced metabolism may have totally different effects. The oedema of muscles during acute sarcocystosis ( Zielasko et al., 1981; Weber et al., 1983 ) has to be explained in a different way. Acute sarcocystosis is accompanied by a crisis of blood circulation followed by extravasation in all tissues, including the muscles. From the results reported in the literature and from our data, it can be concluded that the different developmental stages of Sarcocystis, such as schizonts, young cysts and mature cysts have different effects on the metabolism in muscle tissue. In our experiments, there was no hint of a PSE-syndrome in pigs containing mature cysts, quite the contrary, the relevant measurements gave slightly better results for the infected animals. The observations suggest that the metabolic activities in muscle tissues were slowed down post mortem in the infected animals compared with those of the controls. The mechanism by which sarcosporidial infections influence the metabolism in host tissues are unknown and have to be investigated in further studies, but it is clear that even mild infections with S. miescheriana lead to reduced carcass weights and reduced daily gains. ACKNOWLEDGEMENTS This study was supported by a research grant from the German Research Council (DFG). Special thanks are given to Ms. Martina Walter and Ms. Irmtraud Peters-Greim for excellent technical assistance during this study.
REFERENCES Boch, J., Mannewitz, M. and Erber, M., 1978. Sarkosporidien bei Schlachtschweinen in Siiddeutschland. Berl. Miinch. Tier'~rztl. Wochenschr., 91: 106-111.
31 Bogush, A.A., 1975. (Effect of Sarcocystis invasion on pork quality). Veterinariya (Moscow), No. 8:101-103 (in Russian). Bogush, A.A. and Pyshko, I.I., 1976. (Glycogen content of the muscles and liver of pigs infected with Sarcocystis). Tr. Beloruss. Nauchno-Issled. Inst. Eksp. Vet. (Veterinarnaya nauka ~proizvodstvu), 14:173-174 (in Russian). Creech, G.T., 1922. Sarcosporidiosis of swine, associated with advanced degenerative changes in the musculature. J. Am. Vet. Med. Assoc., 61: 383-392. Eikelenboom, G., Minkema, D. and van Eldig, P., 1976. The application of the halothane test. Differences in production characters between pigs qualified as reactors (MHS-susceptible) and non-reactors. Proc. 3rd Int. Conf. Prod. Dis. Farm Anita., Wageningen, The Netherlands, pp. 183-187. Erber, M. and Geisel, O., 1979. Untersuchungen zur Klinik und Pathologie der Sarcocystis suicanis-Infektion beim Schwein. Berl. Mtinch. Tieriirztl. Wochenschr., 92: 197-202. Fialik, E., Pftitzner, H. and Krause, E., 1984. Routinem~issige Erkennung von PSE-Muskulatur dutch einen elektrophysikalischen Schnelltest. Wiener Tier~ierztl. Monatsschr., 71: 66-70. Schnieder, T. and Rommel, M., 1983. Ausbildung und Dauer der Immunit~t gegen Sarcocystis miescheriana im Schwein bei kontinuierlicher Verabreichung kleiner Mengen yon Sporozysten. Berl. Miinch. Tier'drztl. Wochenschr., 96: 167-170. Sybesma, W., 1966. Die Messung des Unterschiedes im Auftreten des Rigor morris im Schinken. Fleischwirtschaft, 46: 637-639. Weber, M., Weyreter, H., O'Donoghue, P.J., Rommel, M. and Trautwein, G., 1983. Persistence of acquired immunity to Sarcocystis miescheriana infection in growing pigs. Vet. Parasitol., 13: 287-297. Zielasko, B., Petrich, J., Trautwein, G. and Rommel, M., 1981. Untersuchungen fiber pathologisch-anatomische Ver~nderungen und die Entwicklung der Immunit~it bei der Sarcocystis suicanis-Infektion. Berl. Miinch. Tier'drztl. Wochenschr., 94: 223-228.