Update on Pse Research*

UPDATE ON PSE RESEARCH*

DR. W. SYBESMA Research Institute for Animal Husbandry "Schoonoord" Zeist, The Netherlands

Introduction

In recent years the PSE problem has been studied from different angles.

Important issues in this respect are:

Fresh Pork and Technology Physiological Aspc t s Environmental Influences Genetical Aspects

A lot of what is reviewed here is based mainly on the reports of investigators at an International symposium on PSE which was held in 1971 in Zeist. More recent literature is also quoted.

Fresh Pork and Technology

The drip losses in fresh pork and the cooking losses in the cooked end- product have been regarded as those aspects with the heaviest economical impact.

The use of polyphosphates eliminates to a great extent these cookhg losses. Whereas the consumer considers the fat content far more important than the color, PSE meat will hardly give any objections (Zuidam --et al., 1971). Wirth (1972) showed that the pretreatment of the fresh meat with bread crumbs is a pre-condition for preserving the juiciness in PSE. Storage decreases the tenderness more rapidly than in nom1 meat (Buchter and Zeuthen, 1971).

The keepability is prolonged especially if the pH is under 5.3 (Mulder, 1971). Economic losses, although they do exist are fairly slight under present conditions.

* Presented at the 25th Annual Reciprocal Meat Conference of the American Meat Science Association, 1972. Physiological Aspects

Greater economic harm can be attributed to losses from physiological Instability of the mre meaty pig Which shows a higher incidence of PSE. Much research has been directed on endocrinological imbalance of the hypo- physis--adrenal axis (Topel, 1971; Judge and Marple, 1971) and blood parameters to show the physiological effect. Bicknell (1968)names the shock like stress syndrane associated with PSE, the Porcine Stress Syndrome (PSS), whereas Sybesma and Eikelenboom (1969) call it Malignant Hyperthermia Syndrome (MKS) . Circulation aspects have beeri investigated through analyses of the blood gas pattern under stress (Kallweit and Haase, 1971) and (Haase and Steinhaufi 19%). The more stress susceptible pigs develop rather easily acidosis with a high pC02 and because of a probable water shift, a higher hematocrit (Berman and Kench, 1971).

Other parameters such as enzyme-increases Fn the blood after stress are more linked to changes in the muscle tissue under stress.

CPK levels should be reliable indicators for the stress reaction of the animal (Allen --et al., 1971). Bickhardt (1971) feels that this proves the myopathic nature of PSE muscle. Recent1 Allen (1972) showed the confusing fact that tranquilizers (stress reserving3 do increase the CPK level even higher. Not the difference in the potential of glycolysis between PSE and normal muscle tissue but the difference in myofibrillar ATPase activity is of importance in relation to the quick restoration of metabolism (Scopes, 1971).

The muscle metabolism derangement predisposition of PSE is stressed by the investigations of Eikelenboom and Van den Berg (1971), Van Roon (1971), Berman and Kench (1971). Eikelenboom (1972) demonstrated the mlfunction of the mitochondria in PSE prone muscle.

Taking muscle biopsies for predicting meat quality on the basis of the glycolysis intermediates such as G6P, is a practical method for predicting meat quality, i.e. assessing the physiological instability of the pig; (Schmidt et al., 1972).

Environmental Influences

In most countries in Europe, PSE problem and associated transport losses are on the rise (Pohlchristoph, 1969, 1970). The susceptible pigs suffer most from the high environmental temperature (Lendfers, 1971). Barton (1971) showed' the different reaction on the white and red muscle to stress. The shift to a lower pH1 (HE) during a short distance transport is quicker in the first muscle type whereas during a lon transport the red muscle shows more of a tendency to a high ultimate pH $DFD). Stunning is another environmental stress which may affect unfavorably the meat quality. Not only the stunning method itself, providing it is properly used, but especially the pre-stunning treatment has to be considered important in this respect (Ratcliff, 1971; McLoughlin, 1971; Van der Wal, 1971, 1972). Genetical Aspects

Breeding might be effective in reducing the incidence of PSE. Several investigators have found a h2 of about 0.3 for meat color. Barton (1971) found even I h2 of 0.7 for the color of the cured end product. Allen (1971, 1972) is confident CPK estimation in the blood is of value for breeding purposes.

No heterosis in the heredity of the meat quality could be sham in crossbred experiments (Walstra et al. , 1971 ) . In our Institute, we are checking the value of G6P in the ante mortem biopsy sample for use in the performance test. Breed differences are very clear (Walstra, 1972).

Future Research Aspects

Much research has been done in the field of PSE muscle, but until now not much progress is made in diminishing this abnormality. For a part this Is due to the fact that In practice the economical loss of the PSE meat is difficult to assess. The question has to be answered how much damage is really suffered by the industry. Because there is a strong link between the very meaty type pig and PSE muscle, it camnot be expected that by a breeding program based on genetic determined parameters for meat quality the meatiness can be improved together with improving the meat quality.

Therefore also attention has to be drawn to the methods for assessing the meat quality more precisely in the slaughterline (Herring et al., 1971; Scheper, 1972),

The industry should decide then what to do with the different qualities especially PSE. Instead of thinking only of trying to get rid of this abnormality, one should wonder whether it might be possible to change the evil into good. The short time needed for a completed post mortem metabolism, thc: low pH which improves product keepability and the more meaty chops preferred by the housewives are all advantages which have to be explored before we concentrate only on the disadvantages. In this way it would be of great help already to reduce the PSE problem quite impressive.

The higher energy expenditure during stress is in hypertrophied muscle connected with a lactic acid explosion due to the carbohydrate turnover.

Therefore, more research should be done in this respect on the role of the fat metabolism in the muscle during stress (Issekutz, 1970).

Of course, further investigations on the improvement of genetics and environment are also needed. 273

Allen, W. M. and D.S.P. Patterson. 1971. The possible relationship between plasma creatine phospholdmme activity end muscle characteristics in the Pie;. P. 90** Allen, W. M. 1972. Plasma enzymes and muscle characteristics in the pig. Proceedings 2nd Congress Intern. Pig. Vet. SOC. Hannover.

BBlTton, P. A. 1971. Some experience on the effect of pre-slaughter treatment on the meat quality of pigs with low stress-resistance. p. 180.- Barton, P. A. 1971. Personal communication. Be-, M. C. and J. E. Ken&. 1971. Muscle metabolism during anaesthetic induced hyperthermia in pigs. p. 29 .* Bickhardt, K. 1971. Muscle metabolism and enzyme patterns in Iandrace strains with different meat quality. p. 36.* Association of the stress syndrome to sudden death Bicknell, E. J. 1968. losses and post mortem characteristics. "he Pork Industry, ed. D, Topel. ~owaState University Press, p. 26.w

Buchter, L. and P. Zeuthen. 1971. The effect of aging on the organoleptic qualities of PSE and normel pork loins. p. 247.M

Eikelenboom, G. and S. G. van den Bergh. 1971. Aberrant mitochondrial energy metabolism in stress-susceptible pigs. p. 66 .*

Eikelenboom, G. 1972. Stress susceptibility in swine and its relationship with energy metabolism in skeletal musculature. Thesis, Utrecht . Haase, S. and D. Steinhauf. 197l.. Effects of stress on some oxygen metabolism parameters Fn boars. p. l9l.w

Herring, H. K., J. H. HWand L. J. Hausen. 1971. Studies on chemical and physical properties of pork in relation to quality. J. him. Sci. 33:578. Issekutz, B. 1970. Interrelationship of free fatty acids, lactic acid and glucose in muscle metabolism. The physiology and Biochemistry of Muscle as a Food, 2. Ed. E. J. Brisky, R. G. Cassens and B. B. Marsh. The University of Wisconsin Press .

Judge, M. and D. Ne Marple. 1971. Adrenal insufficiency in stress- susceptible pigs. p. 47 .*

Gillweit, E. end S. Haase. 1971. The effect of short-term climatic stress on pigs. p. 197.H 274

Lendf'ers, L.1I.H.M. 1971. Loss of pigs due to death during transport; a one-year-survey at an abattoir. p. 225.w Vcbughlin, J. V . General introduction, stunning (the death reaction and metabolism post19n. mrtem of porcine skeletal muscle). p. 123 .w

Mulder, S. J. 19n. Houdbaarheid en kwaliteit van ?=--en DFD varkensvlees . C.I.V.0. Rapport nr. R. 3669. Pohlchristoph, H. 1970. Uber die Verladung und Beforderung lebender Tiere mit der Bundesbahn und auf Lasthaftwagen. Schlact -und Viehof Zeitung . 69-487 (19691, 70-5 (19701, 70-41 (1970) '

Ratcliff, P. W. 1971. Review of stunning. p. 133.M

Roon, P. S. van. 1971. Respiratory rate and oxidative phosphorylation of sarcosome8 from m. longissimus dorsi as related to pH, determined at two moments post mortem. p. 81.* Scheper, J. 1972. Qualitatsabweichungen bei Schweinefleisch. Genetische und Unweltbedingte Einflusse. Die Fleischwirtschaft 52-203.

Schmidt, G. R., L. Zuidam and W. Sybesms. 1971. Biopsy technique and analyses for predicting pork quality. p. 73.w

Scopes, R. K. 1971. Mechanisms controlling glycolysis in muscle. me Biochemistry of post mrtem glycolysis. 17th European Meeting of Meat Research Workers, Bristol.

Sybesma, W. and G. Eikelenboorn. 1969. Malignant hyperthermia syndrome Fn pigs. Neth. J. Vet. Sci. 2:155.

Topel, D. G., D. G. Siers, G. M. Weiss and J. H. Msgilton. 1971. Some physiological and biochemical characteristics of normal and stress prone pigs. 17th European Meeting of Meat Research Workers, Bristol.

Wal, 2. G. van der. 1971. Stunning, sticking and exsanguination as stress factors in pigs. p. 153.M Wal, P. G. van der. 1972. Sinflusz der elektrischen Retaubung auf Schlahtschweine--Veranderungen im Blut . Deutsch. Tierarztl. Wschr . 79-16.

Walstra, P., D. Minkema, W. Sybesma and J.G.C. van de Pas. 1971. Genetic aspects of meat quality and stress resistance in experiments with various breeds and breed crosses. Meeting European Association of Animal Prodiction, Versailles. Walotra, P . 19-72, Personal comication. 275

Zuidam, L., C. R. Schmidt, J. Oosterbaan and W. Sy-besma. 1971. Effect of fresh pork color on consumer acceptance. p.

+E Proceedings of the 2nd International Symposium on Condition and Meat Quality of Pigs, Zeiet, March 22-24, 1971. C. E. AW: A couple of years ago, I believe, we started this committee and we are continuing it because we felt it was appropriate for the American Meat Science Association in this conference to look at other pmrces of protein than red meat and you see the times develophg when we see more combination kinds of products and we feel that this is simply broadening our horizons and hopefully bringing to light information that will be helpful in industry and in our teaching assignments. The center of the topic this year has to do with poultry products, which I'm sure some of you know are rather close to my heart and perhaps that's why it's on the program. The chairman of this committee is Dr I Paul Addis, my associate at the University of Minnesota and, Paul, I welcome your comit Lee report.

P. B. ADDIS: Thank you, Gene, for those comments about the reasms why we have a protein source committee and why we consider different sources of protein in the American Meat Science Association. Many of the univcrsities and industrial organizations dealing with meats are expanding to include poultry as part of their program and in their curricula. I hope this session will help us to become a little more able to do this type of' integration. I would like to thank Rr. Charlie Cook, who could not be here today, for his work on the committee. The other members of the cormittee will be participating on the program. Our first speaker today, Dr. Bill Marion, is a professor in the Animal Science Department with a joint appointment in Food Technology at Iowa State University. Dr. Marion received his B.S. degree in Kentucky at Berea College, and went on to Purdue University for his M.S. and F'h.D. work. It's interesting to note that we have today an academic father and son team because, at Purdue, Dr. Marion studied under Dr. Stadelmas who is our second speaker. Dr. Marion's research has been involved with postmortem changes in turkey muscle and more recently he is studying the storage stability and effects of the tocopherol feeding on stability of lipids in turkeys. We feel he is very well qualified to speak to us today and might also add that he was responsible primarily for the barbecue that we had Monday night. I think with qualifications of that sort we're happy to welcome Dr. Marion to speak on the subject of biological and chemical factors in poultry muscle relating to quality.