270. P O R C I N E P H Y S I O L O G Y AS R E L A T E D TO POST-MORTEM M U S C L E P R O P E R T I E S J. C. FORREST The importance of many of t h e manifestations of ante-mortem physiological f a c t o r s have been recognized f o r several years-particularly those which a r e associated with environment and stress. Some of t h e e a r l y work with t h e problem of dark c u t t i n g beef conducted here a t Kansas State by Professor Mackintosh and Dr. Hall,(Hall e t a l. 1944), provided a b a s i s f o r believing t h a t ante-mortem physiology was influenced by ante-mortem environment and was important i n a f f e c t i n g post-mortem muscle properties. These e a r l y observations were f u r t h e r subs t a n t i a t e d by Lawrie (1958) and Hedrick (1959). Workers a t M s s o u r i (Hedrick e t a l. 1961) Purdue, JuSge e t a l. (1963) and Kansas (Forrest e t a l. 1964) have shown t h a t ante-mortem s t r e s s i s a l s o important i n lambs. Some of t h e f i r s t evidence of the profound e f f e c t which ante-mortem physiological f a c t o r s had on ultimate porcine muscle was presented by Briskey e t a l. (1959"jb) when they demonstrated the e f f e c t of d i e t and exercise on t h e occurrence of pale, s o f t, exudative pork. The influence of environment on t h e post-mortem muscle p r o p e r t i e s has been established i n r e p o r t s by Ludvigsen (1954), Judge -e t a l. (1959). Sayre e t a l. (1961) (1963) Forrest e t a l. (1963), Kastenschmidt e t a l. (1964) ( 1 9 6 5 ) a n d A d d i s (1965). Since t h e term physiology encompasses t h e e n t i r e gamit of b i o l o g i c a l function, it becomes necessary t o define t h e limits f o r discussion i n t h i s paper. We w i l l be concerned primarily with some of t h e physiological parameters which permit an animal t o cope with i t s immediate environment. Specifically, we w i l l be concerned with h e a r t r a t e, r e s p i r a t i o n r a t e and two blood gases O2 and C 0 2 as well as blood ph. The influence of environment on t h e physiological parameters mentioned i s complex and a s yet only l i m i t e d work has been reported on l a r g e laboratory animals. Robinson and Lee (1941) and Ingram (1964) demonstrated t h a t h e a r t and r e s p i r a t i o n r a t e s increase a s r e c t a l temperature increases i n t h e pig. I n a recent study (Forrest e t a l. 1965), w e observed t h a t i n unt r e a t e d animals, h e a r t and r e s p i r a t i o n r a t e s determined immediately p r i o r t o slaughter tended t o be higher i n those animals which ultimately became PSE. This r e s u l t has been f u r t h e r substantiated i n another group of 33 Poland China and Chester White pigs. I n studying t h e influence of a w a r m environment, w e observed t h a t some animals increased i n h e a r t rates while others decreased i n h e a r t rate a s
271. a r e s u l t of t h e w a r m treatment. It was observed however t h a t t h e p r e - t r e a t ment h e a r t rates were considerably higher than t h e normal r e s t i n g rates i n a p i g which may explain why some animals decreased i n h e a r t r a t e upon exposure t o t h e w a r m environment. The most i n t e r e s t i n g point of t h i s observation i s shown i n t h e next s l i d e, which i l l u s t r a t e s t h e f a c t t h a t t h e animals which already had high h e a r t r a t e s and responded t o t h e w a r m treatment by increasing h e a r t rate, produced PSE muscles, while those which decreased i n h e a r t rate when placed i n t h e w a r m environment chamber had noma1 niuscle. To f u r t h e r e l u c i d a t e some of t h e changes which occur during t h e w a r m environmental treatment an experiment was designed t o study h e a r t and r e s p i r a t i o n rate and t h e c h a r a c t e r i s t i c s of venous blood i n two breeds of p i g s subjected t o a w a r m environmental treatment. Resting h e a r t and r e s p i r a t i o n rates were determined on 6 Poland China and 6 Chester White p i g s a t least 1 2 h r. p r i o r t o experimentation. Resting rates were determined by placing a l e a t h e r belt around t h e body of t h e p i g t o hold two needle electrodes which were i n s e r t e d d o r s a l l y t o the l e f t of c e n t e r l i n e and p o s t e r i o r t o t h e scapula and v e n t r a l l y t o t h e l e f t of c e n t e r l i n e and p o s t e r i o r t o the f o r e limbs. The animals were allowed t o become accustomed t o t h e apparatus. Rates were determined only after t h e animal had remained i n a prone p o s i t i o n for a t least 30 min. Three p i g s of each breed w e r e designated as c o n t r o l s and placed i n t h e c o n t r o l l e d environment temperature chamber f o r 30 min. a t room temperature The other t h r e e p i g s of each breed were subjected t o a warm en(22oc.). vironment (5OOC.) i n t h e same chamber f o r 30 min. All other conditions were h e l d constant ( a s much as possible and p r a c t i c a l for a l l 1 2 animals). A blood sample was c o l l e c t e d anaerobically from t h e j u g u l a r vein of each animal before and after t h e 30 min. period i n t h e environmental chamber. PC02, PO2 and p H of t h e s e samples were determined using t h e Beckman Model 160 Physiological Gas Analyzer shown i n t h e next s l i d e. Heart and r e s p i r a t i o n rates were determined before t h e animals were placed i n t h e chamber and a t 5 min. i n t e r v a l s during t h e t i m e t h e animal w a s i n t h e chamber. The c o n t r o l l e d environment chamber and Cardiopan electrocardiograph which w a s used f o r determining h e a r t and r e s p i r a t i o n rates a r e shown i n t h e next s l i d e. The animals were exsanguinated immediately a f t e r c o l l e c t i o n of t h e last blood sample. A muscle sample w a s excised f r o m t h e right longissimus d o r a l muscle i n an area p o s t e r i o r t o t h e l a s t t h o r a c i c v e r t e b r a immediately a f t e r exsanguination. ph, t i m e course of r i g o r mortis and response t o e l e c t r i c a l stimulation were determined on t h i s sample. The next s l i d e shows t h e apparatus used f o r e l e c t r i c a l stimulation. The stimulation procedure p e r se w i l l be discussed more f u l l y i n t h e next paper. The rate of ph d e c l i n e was determined by measuring muscle ph on t h e f r e s h l y cut muscle surface a t 0, 15, 30, 45, 60, 1 2 0, 180 min. post exsanguination. Samples of t h e longissimus d o r s i and gluteus medius muscle were also scored s u b j e c t i v e l y f o r color-morphology a t 24 h r. post-mortem.
272. Results The next slide shows that in the control group, longissimus dorsi muscle from animals of both breeds were nearly normal with the exception of one Poland China which became pale, soft and exudative. On the average muscle gross morphology ratings fromthe Chester Whites were slightly lower than those from the Poland Chinas (2.2 compared to 2.3). The next slide shows that in the warm treatment group all the Poland Chinas had longissimus dorsi muscles which were extremely pale, soft and exudative at 24 hr. post-mortem. All the Chester Whites had normal longissimus dorsi muscles at 24 hr. post-mortem. Similar results were observed in the gluteus medius muscles. These subjective color-morphology ratings were further substantiated by the observation that all animals in the central group, with the exception of the PSE Poland China, had a slow rate of post-mortem ph decline, long time course of rigor mortis and strong response to electrical stimulation. Conversely the Poland Chinas in the warm treatment group had a fast rate of post-mortem ph decline (5.8 at 30 min.), reached the onset of rigor mortis in less than 15 min., and did not respond to electrical stimulation. The Chester Whites from the warm treatment group had a slow rate of postmortem ph decline (5.8 at 2 hr. ), average onset of rigor mortis at 113 min. post-mortem, and responded strongly to electrical stimulation. In agreement with previous observations resting heart and respiration rates were considerably lower than the rates observed on standing animals immediately prior to treatment. Resting heart and respiration rates were not observed to be significantly different between breeds. The next slide shows the influence of treatment on mean heart rate for the two breeds. During the control period in the environmental chamber the heart rates decreased slightly in both breeds. In general rates tended to be slightly higher in the Poland Chinas, this higher average rate was due to the animal which was observed to be ultimately pale, soft and exudative. The Poland Chinas which were subjected to this warm environment exhibited a sharp increase in heart rate reaching an average of 268 beats/min. Ten min. after the beginning of treatment all three Poland Chinas were removed fromthe chamber and exsanguinated after 20 min. or less. Animals from the Chester White breed which were subjected to the warm treatment, had heart rate which dropped below the pre-treatment level and at the end of the treatment period the rates were only slightly higher than the pre-treatment levels. The next slide shows the influence of treatment on respiration rates. During the control period in the chamber respiration rates in both breeds did not appear to be significantly different. The respiration rates tended to increase during the first 15 min. treatment and then decreased toward the end of 30 min. treatment period.
273. I n t h e w a r m treatment group t h e Poland Chinas exhibited a sharp r i s e and subsequently showed a fast d e c l i n e i n r e s p i r a t i o n r a t e. This change i n r e s p i r a t i o n rate w a s one t o r e s p i r a t o r y a r r e s t and was t h e reason t h e animals had t o be removed f r o m t h e chamber and exsanguinated before t h e end of t h e treatment period. Respiration rates i n t h e Chester Whites showed continuous i n c r e a s e s during t h e warm treatment period. Blood gas and blood ph d a t a c h a r a c t e r i z e some of t h e breed d i f f e r e n c e s previously described. The c o n t r o l Poland China p i g s exhibited no change i n FC02 or ph during t h e t i m e t h a t they were i n t h e chamber. The Chester Whites exhibited only a small decrease i n PC02 and r e t a i n e d similar ph values. The Poland China p i g s which were subjected t o w a r m treatment showed s i g n i f i c a n t increases i n FCOz during treatncent, however t h e PO2 values decreased d r a s t i c a l l y during t h e same t i m e period. I n one case no free O2 w a s detected i n t h e blood a f t e r treatment. ph of t h e blood a l s o dropped s i g n i f i c a n t l y from 7.4 t o 6.8. Conversely t h e Chester Whites decreased i n blood PC02 during t h e w a r m treatment and showed a s l i g h t increase i n PO2 (not s i g n i f i c a n t ). Data f r o m another study (Judge e t a l. 1965) h d i c a t e s t h a t physiological adjustments made by Chester White p i g s during t h e s t r e s s of r e s t r a i n t may be governed more c l o s e l y by endocrine f a c t o r s than those adjustments made by Poland Chinas. From t h e s e r e s u l t s it appears t h a t c i r c u l a t o r y and r e s p i r a t o r y d i f f i c u l t i e s leading t o increased blood PC02 and decreased PO2 can be major c o n t r i b u t o r s t o t h e production of pale, s o f t, exudative muscle, p a r t i c u l a r l y i n animals which are subjected t o warm temperature and stress such as would be encountered i n trucking animals t o market. I n s w a r y, t h e l i m i t e d evidence now a v a i l a b l e i n d i c a t e s t h a t t h e physiological response of an animal t o i t s ante-mortem environment has a strong influence on changes which occur i n i t s post-mortem muscle. A s techniques and f a c i l i t i e s f o r l a r g e animal physiological research become a v a i l a b l e more i n t e n s i v e s t u d i e s may e l u c i d a t e t h e causes and c o n t r o l s of t h e complex r e a c t i o n s of an animal t o i t s environment, and l e a d t h e way t o producing and marketing animals which w i l l y i e l d uniformly high q u a l i t y meat products. L i t e r a t u r e Cited Addis, P. B., M. D. Judge, H. R. Johnson and N. W. Thomas, 1965. Relationship of environmental temperature and humidity during growth t o t h e incidence of pale, s o f t, exudative porcine muscle. J. Food Sci. (Submitted). Briskey, E. J., R. W. Bray, W.,G. Hoekstra, R. H. Grummer and P. H. P h i l l i p s. 195ga. T h e effect of various l e v e l s of exercise i s a l t e r i n g t h e chemical and physical c h a r a c t e r i s t i c s of c e r t a i n pork ham muscles. J. Aninal Sci. 18:153-157.
274. Briskey, E. J., R. W. Bray, W. G. Hoekstra, P. H. P h i l l i p s and R. H. Grummer. I95gb. The e f f e c t of exhaustive exercise and high sucrose regimen on c e r t a i n chemical and physical pork ham muscle c h a r a c t e r i s t i c s. J. Animal Sci. 18:173-177. Forrest, J. C., R. F. Gundlach and E. J. Briskey, 1963. A preliminary survey of the v a r i a t i o n s i n c e r t a i n pork ham muscle c h a r a c t e r i s t i c s. R o c. of t h e 15th Research Conf., American Meat I n s t i t u t e Foundation. Forrest, J. C., R. A. Merkel and D. L. Mackintosh. 1964. Influence of pre-slaughter treatment upon c e r t a i n physical and chemical characteri s t i c s of ovine muscle. J. Animal Sci. 23:551-554. Forrest, J. C., L. L. Kastenschmidt, G. R. Beecher, R. H. Grumer, W. G. Hoekstra, and E. J. Briskey, 1965. Porcine muscle properties. B. Relation t o n a t u r a l l y occurring and a r t i f i c i a l l y - i n d u c e d variat i o n i n h e a r t and r e s p i r a t i o n rates. J. Food Sci. 30:492. H a l l, J. L., D. L. Mackintosh and C. E. Latschar. 1944. Quality of Beef. P a r t IV. C h a r a c t e r i s t i c s of dark c u t t i n g beef, survey and preliminary investigation. Kansas Agr. Exp. Sta. Tech. Bul. 58. Hedrick, H. B., J. B. B o i l l o t, D. B. Brady and H. D. Nawnann. 1959. Etiology of dark-cutting beef. Mo. Agr. Exp. Sta. Res. Bul 717. Hedrick, H. B., J. B. B o i l l o t, A. J. Dyer and H. D. Naumann. 1961. Effect of ante-mortem administration of adrenalin on post-mortem lamb carcass c h a r a c t e r i s t i c s. J. A n i m a l Sci. 20:558. Ingram, D. L. 1964. The e f f e c t of environmental temperature on body temperature, r e s p i r a t o r y frequency and pulse r a t e i n t h e young pig. Res. V e t. Sci. 5:348. Judge, M. D., V. R. C a h i l l, L. E. Kimkle, and W. H. Brunner. 1959. Pork quality. I. Influences of some f a c t o r s on pork muscle c h a r a c t e r i s t i c s. J. A n i m a l Sci. 18:448. Judge, M. D. and M. Stob. 1963. S t r e s s during growth. I. Effects on physiology, carcass composition, and carcass q u a l i t y of lambs. J. A n i m a l Sci. 22:1059. Judge, M. D., J. C. Forrest, W. G. Hoekstra, and E. J. Briskey. 1965. Porcine endocrine r e l a t i o n s h i p s. I. Heart and r e s p i r a t o r y r a t e s. ( I n preparation) Kastenschmidt, L. L., E. J. Briskey and W. G. Hoekstra. 1964. Prevention of pale, s o f t, exudative porcine muscle through regulation of antemortem environmental temperature. J. Food Sci. 29:210. Kastenschmidt, L. L., G. R. Beecher, J. C. Forrest, W. G. Hoekstra, and E. J. Briskey. Porcine muscle properties. A. Alteration of glycolysis by a r t i f i c i a l l y induced changes i n ambient temperature. J. Food Sci. (In press).
Lawrie, R. A. 1958. Physiological stress in relation to dark-cutting beef. J. Sci. Food Agr. 9:721. Ludvigsen, J. 1954. Undersogelser over den sakaldte "Muskeldegeneration" Hos svin. Beretning fra forsogslaboratoriet Udgivet of Statens Husdrybrugsudvalg 1:272. Robinson, K., and D. H. K. Lee. 1941. Reactions of the pig to hot atmospheres. Proc. Roy. SOC. Queensland 53:154. Sayre, R. N., E. J. Briskey, and W. G. Hoekstra. 1953. Alteration of post-mortem changes in porcine muscle by preslaughter heat treatment and diet modification. J. Food Sci. 28:292. Sayre, R. N., E. J. Briskey end W. G. Hoekstra. 1963. Effect of excitement, fasting and sucrose feeding on porcine muscle phosphorylase and post-mortem glycolysis. J. Food Sci. 28:472. V. R. CAHILL: Thank you John, for those very stimulating remarks. I can see many ramifications of some of these ideas whether it be in the carcass contest story we are going to hear later or in the food which we eat each day, even for breakfast in Kansas. As we move now to the more Specific Biological Features of Post-Mortem Change in Porcine Ibbscle we are calling on our good friend J. D. Sink who has seen fit to direct his postdoctorate effort in this particular area, so, John, we will turn the mike to you.