Maataloustieteellinen Aikakauskirja Vol. 61: 415—423, 1989 Influence of selection phase, fasting and transport on porcine stress and on the development of PSE pork MARKKU HONKAVAARA Finnish Meat Research Centre, Box 56, SF-13101 Hämeenlinna, Finland Abstract. The objectives were to investigate the effect of selection phase, fasting time and transportation on porcine stress and on the occurrence of pale, soft and exudative (PSE) pork. The first selected pigs had the lowest blood creatine kinase (CK) activity and were least susceptible to PSE development. Whereas, the second selected animals were most stressed during transport and showed the highest frequency of PSE. On the other hand, the last selected pigs had elevated CK values from the farm up to stunning, and also showed a slow pH fall in M. tongissimus dorsi (LD) 45 min postmortem (p.m.). Furthermore, the pigs of the first and last selection had, respectively, the lowest and highest lean meat content. Muscle traits such as glycogen and lactate content 0 min p.m. and pH 45 min p.m. sug- gested that the most acceptable pork quality for meat products manufacture could be obtained after a fast of 6—7 hif the pigs were fed twice a day. Whereas, overnight holding had a nega- tive effect on muscle glycogen and lactate content. During transport, pigs were under greatest stress if they were loaded just before feeding period, or if they were transported in warm weather (over 10°C). Moreover, high mortality and CK values occurred at the same external temperatures during transportation. In addition, increased transport time elevated the CK activity from the farm up to the abattoir. Index words: selection phase, fasting, transport, creatine kinase, PSE meat Introduction Pigs fed a restricted ration twice a day showed much more variation in glucose flux rate, rate of formation and hydrolysis of glycogen than pigs fed ad libitum (Rus and Grummer, 1969). Easily mobilized glycogen stores were exhausted in about 20 h. Pigs fed ad libitum most likely had an almost constant glycogen reserve, whereas the labile glycogen depots of pigs fed a restricted ration were pre- sumably nearly exhausted in the morning be- fore feeding (Rus and Grummer, 1969). Pospiech et al. (1981) observed that the highest number of pigs with muscle defects of PSE and DFD type occurred in groups of 90 415 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=Fa_OGhT3gT0vUWo-.6LiQoYywcugso_QowcoZ7w.B-fCmbpCeGSbLgUHMTVNTXsIQTlTxhd1BYWc_mm84GR5XUOor9E4MZT69Kb6lwI-3z1o2BU2oLECwcfQGbFJNYaL-fQBeeU1bJcpVrv6GF1oNOItshFkf17No5sntrsBnx1pdNRFtb0GE6-mcS3E0wc8r5fFGniELybtxLwiDA and 120 kg live-weight. Lower meat quality was perhaps caused by the change in metabo- lism. In the group of 90 kg it was probably connected with the change of proteins to car- bohydrates proportion in the fodder. The cause of the poorer meat quality of 120 kg pigs could be the slowing down of muscle tissue synthesis (Pospiech et al., 1981). For practical purposes only those factors which affect energy reserves in the muscle at the point of slaughter were important for meat quality (Barton-Gade, 1985). If PSE and DFD meat were considered equally important, then slaughter of unfed pigs immediately af- ter unloading and slaughter of fed pigs after a holding period of about four hours gave the lowest frequency of both PSE and DFD (Nielsen, 1981). Withholding food during the 12-hourperiod prior to transportation was a simple way to reduce death during transport (Williams, 1985). Earlier work (Honkavaara, 1989) consid- ered the influence of porcine stress on blood composition and early p.m. meat quality in pigs of different halothane genotypes. The purpose of this study was to investigate the effects of selection phase, fasting time and transportation of porcine stress and meat quality. In addition, it was studied the effect of transport temperature and time on mortal- ity of pigs. Material and methods Test animats The test animals consisted of 103 pigs of which one died during transport. They were from the following breeds; 39 Finnish Land- race (L) and 8 Finnish Yorkshire (Y) pigs, and 56 LxY crosses. 11—12 pigs were collected per month from September 1985 to May 1986. 31, 12, 8 and 4 pigs came respectively from 1,2, 2 and 8 producers. Treatments were repeated 22 times, and the programme of one treatment is described earlier (Honkavaara, 1988). 28, 24 and 50 pigs were slaughtered at the abat- toir in Nurmo, Forssa and Salo, respectively. The pigs were selected in three phases. Thus theanimals of the first, second and last selec- tion gained the slaughter weight of 90—120 kg first, second and third, respectively. Farmers evaluated the weight of pigs by measuring or weighing. After blood sampling, marking and tattooing, the test animals were not separated from other pigs at farm. Moreover, all pigs were treated in the same way from the farm up to the point of stunning. Furthermore, data were collected from the last feeding time of day, loading time of day, transport tempera- ture and duration. In order to compare the influence of trans- port temperature and time on mortality with the CK values of the test pigs after transport, data were collected from a further 317 pigs which have died in trucks in 1986. Evaluation of porcine stress and meat quality Methods used for the evaluation of porcine stress and meat quality are presented earlier (Honkavaara, 1988). Variables The collected data included the following 20 continuous variables: loading time of day (LT), transport temperature (TT), transport duration (TD), durationof lairage (DL), tem- perature of lairage (TL), humidity of lairage (HL), stunning time of day (ST), fast dura- tion (FD, time elapsed between feeding and stunning), carcass temperature 0 min p.m. (CTO ), blood creatine kinase (CK) activity on farm (CKF), CK activity during unloading (CKU), CK activity at exsanguination (CKE), serum glucose (SG), serum glycerol (SGL), se- rum lactate (SL), serum pH (SpH), muscle glycogen 0 min p.m. (MG O), muscle lactate 0 min p.m. (MLO), pH in the M. longissimus dorsi (LD) 45 min p.m. (pH,) and carcass hot weight (CW). Also carcass grading class (CC) was included as an uncontinuous varia- 416 Die in the analysis. The CKF, CKU and CKE values were log l 0 transformed. Statistical analyses Conventional statistical methods were used to calculate means, standard deviations and standard error of the means (SEM). In order to examine significant relations between the variables and differences among the means, data were analysed by simple regression and by analysis of variance, respectively. Further- more, to evaluate the influence of the varia- bles on porcine stress and meat quality, a step- wise linear regression analysis was performed (statistical program Pato for microcomputers, Mikrovuo Ky, Finland). The regression model (1) included the de- pendent variable Y, (i=l—9), the 20 in- dependent variables Xj 0 = I—2o, and the standardized regression coefficients B, 0 = I—2o, j*i). Y, =B.X, + B 2X 2 + B 3 Xj + ... + 820B20 X20 (1) Regression analysis computed the combina- tion of the most contributing independent variables to the regression model. The pro- gram added to the model that variable which fulfilled the F-ratio criterion (F>3) and had the maximum coefficient of determination (R 2). The variables which made minor contri- butions (F<2) were deleted from the model. Finally the program printed the chosen mod- el which estimated the dependent variable best. This output included the coefficient of determination, F ratio, significance of contri- bution, chosen independent variables and their standardized regression coefficients, par- tial regression coefficients, F values, sig- nificance levels and contributions. On the basis of stepwise regression, the prediction equations (2) were developed using the independent variables described above. Yj = B„+ B,X, + B 2X 2 + ... + B„X n (i= I—9, n = 3—5) (2) Results Prediction ofporcine stress and meat quality Table 1 shows the combined effects of the studied variables on porcine stress and meat quality. The former was evaluated by blood CK activity, serum values and carcass temper- ature, while the latter was estimated by mus- cle glycogen, lactate and pH, value. Thus the coefficient of determination (R2 100) of the prediction equations was highest for carcass temperature (62.7 %), serum lactate (61.0 %) and glucose (60.7 %), and log CK at exsan- guination (57.1 %). Whereas R 2 100 de- creased for muscle lactate (35.3 °7o) and glyco- gen (28.5 %) serum glycerol (22.7 %) and pH (19.7 %), and log CK during unloading (16.4 %). The combined effects of the in- dependent variables of the prediction equa- tions are discussed below. Selection phase Table 2 shows theblood characteristics and the carcass traits studied in the three selection phases. The occurrence of reactors was 0, 7.6 and 4.2 % in the first, second and last selec- tion, respectively. No significant differences were found between the three phases in log CK at exsanguination that was one of the most contributing components for carcass temper- ature (partial R 2 100=12.9 °7o, Table 1). Pigs of the first selection were stressed least. Thus they had the lowest CK values and the lowest content of muscle lactate. In addition, they had a moderate pH fall in the LD mus- cle 45 min p.m. that made them most accept- able for meat products manufacture. This was based on the fact that carcasses which had a fast pH fall 45 min p.m. developed PSE meat, whereas those with a slow pH fall could de- velop dark, firm and dry (DFD) meat in higher frequencies than those with a moder- ate pH fall. Actually, our unpublished results indicated that about 20 % of the carcasses with pH| values over 6.4 developed DFD in the LD next day. 417 418 Table I. The best stepwise regression models3 for predicting the characteristics of porcine stress and meat quality. Prediction equations6 R’ 100 DfJ % Log CK during unloading = 2.782 —0.159LT 0.129TT +0.327TD +o.l4llogCKF Log CK at exsanguination= —9.933 —O.3OBLT + 0.652CT„ + O.27SGL —O.2BBMGO +O.2IBIogCKU Serum glucose = 1.027 -0.164TD + 0.6475 L -0.201 IogCKE Serum glycerol = -19.974 - 0.378TT+ 0.2465 L + O.IB9SpH + 0.24210gCKE Serum lactate = -0.521 + 0.22FD +0.6655G +0.1545GL +0. HIogCKF Serum pH = 8.03 + 0.138TT+ 0.167TD +0.1935GL - 0.3185L Carcass temperature= 35.331 + 0.40LT +0.501TT +0.32910gCKE Glycogen of LD = 6.435 - 0.241TT -0.222FD -0.189ML„ +0.202 C W -O.I9SIogCKE Lactate of LD = 7.907 + 0.49TD - 0.2165T - 0.189MG0 - 0.203pH, + 0.173CC 16.4 4/88 57.1 5/47 60.7 3/86 22.7 4/85 61.0 4/85 19.7 4/85 62.7 3/53 28.5 5/89 35.3 5/89 “ Regression models have significant F-values (P<0.01). b Abbreviations given in text. c Coefficient of determination x 100 d Degrees of freedom. Table 2. Mean values of studied variables in three selection phases. Trait Selection phase SEM First Second Last Log CK on farm, U/l Log CK during unloading, U/l Log CK at exsanguination, U/l Serum glucose, mmol/l 3.0 3.2 3.2 0.03 3.0“ 3.4 b 3.2 0.04 3.2 3.4 3.5 0.05 5.6“ 5.0“ 7.8 b 0.05 Serum glycerol, mmol/l Serum lactate, mmol/l Serum pH 0.5 0.5 0.6 0.003 0.0613.3“ 12.2“ 16.7b 8.0 8.1“ 7.8b 0.03 Carcass temperature, °C Glycogen of LD, pmol/g Lactate of LD, pmol/g Fasting time, h 39.3“ 38.6 38.Ib 0.13 27.2“ 30.2“ 23.5b 0.20 38.9 45.6 45.6 0.11 22.3“ 17.5b 21.2“ 0.52 pH,<5.B, % 5.8