3 Maataloustieteellinen A ikakauskirja Vol. 61: 425—432, 1989 Influence of lairage on blood composition of pig and on the development of PSK pork MARKKU HONKAVAARA Finnish Meat Research Centre, Box 56, SF-13101 Hämeenlinna, Finland Abstract. The purpose of this study was to investigate the effect of lairage temperature, humidity and time on blood composition and on the development of PSE meat (pH,<5.B). The present study suggested that holding temperature and time had a major influence on porcine stress and meat quality, whereas, lairage humidity had a minor effect on these traits. The higher was lairage temperature the higher carcass temperature(P < 0.001) and log creatine kinase (CK) value (P<0.05) at slaughter. Prolonged holding time increased muscle glycogen content (P<0.01) and muscle pH, value (P<0.05) but decreased muscle lactate content in pigs slaughtered on transport day. In summary, the results suggested that the optimum lairage temperature, humidity and time were respectively 15—I8°C, 59—65 % and 3—5 h. These resulted in a low muscle lactate content and PSE frequency, whereas muscle glycogen level was high and pH, in tongissimus (torsi (LD) muscle was in the range of 5.9—6.4 which was acceptable for commercial use. Index words: abattoir, lairage, blood composition, creatine kinase, PSE meat Introduction During lairage, pigs are exposed to a strange and fluctuating environment which might be stressful for them. Therefore, meat quality could be improved by minimizing these fluc- tuations and by proper handling of animals. Pigs held in fluctuating temperatures (21 32°C) or in conditions of 37°C and 100 °7o relative humidity (RH) yielded carcasses with a more rapid postmortem (p.m.) glycolytic rate than did pigs reared at a constant 27°C in a moderate 38—42 % RH (Cassens et a!., 1975). At the abattoir, even a moderate and short physical stress influenced plasma lac- tate, glucose and pH values (Kolczak and Kraeling, 1986; Lannek, 1976; van der Wal, et at., 1985). Dzapo et ai (1981) found that the com- bined effect of blood CK value and rectal tem- perature accounted for meat quality defects. Moreover, blood CK activity was significant- 425 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=eqPab19U_33v6VGg.Mgzw-HFZ9eVLpPwuCtygfQ.EIp1LL6cBdqWgCPnEUTd_ieGpcnz6rtO5hkS31ZLgyC3Z7HLir5gjuldKyfx_9-pyLRZ3BK9i1Kx97Xr5LlCw9TdhwTP5eQM50Jr9UJFpl-GeiYaXaaDCXM1KE2qtjxDIbZsZekNnBq43JX8TguupwOMQLCstAARbehW1ExctQ 426 ly correlated with muscle pH and U.S.D.A marbling score (Addis et al., 1974). Further- more, a high carcass temperature was closely related to a rapid pH fall and the onset of rigor which developed PSE meat (Sybesma and van Logtestijn, 1966; Woltersdorf and Troeger, 1987). Earlier papers (Honkavaara, 1988 and 1989) considered the effect of porcine stress on blood composition and early p.m. meat quality in pigs of different halothane geno- types, and the influence of selection phase, fasting and transport on porcine stress and on the occurrence of PSE. The purpose of this study was to evaluate the effect of lairage tem- perature, humidity and time on blood com- position and on the development of PSE meat. Material and methods Treatment during lairage This study was conducted for nine months from September 1985 to May 1986 by collect- ing 11—l2 pigs per month. The collection of test animals and their treatment programme are described earlier (Honkavaara, 1988). Thus six, six and ten treatments were carried out at the abattoir in Nurmo, Forssa and Salo, respectively. Each treatment consisted of four to eight pigs from one producer. Consequent- ly, 28, 24 and 50 pigs were slaughtered at the abattoir in Nurmo, Forssa and Salo, respec- tively. During unloading, blood drops from the ear vein of test pigs were collected on filter paper test cards (Honkavaara, 1988). During lairage, the test animals were held in one box, separated from the rest of pigs. Finally they were slaughtered with the otheranimals of the same producer. The temperature and humidity of lairage were measured with a portable hygrometer (Humicap HMI 31, Vaisala, Finland). Lairage duration was the time (min) elapsed between unloading and stunning. Evaluation of porcine stress and meat quality Methods used for the evaluation of porcine stress and meat quality are described earlier (Honkavaara, 1988). Variables The following 16 “lairage variables” were collected: external temperature (ET), dura- tion of lairage (DL), temperature of lairage (TL), humidity of lairage (HL), fast duration (FD), carcass temperature 0 min postmortem (p.m., CT0), blood creatine kinase (CK) ac- tivity during unloading (CKU), CK activity at exsanguination (CKE), serum glucose (SG), serum glycerol (SGL), serum lactate (SL), se- rum pH (SpH), muscle glycogen 0 min p.m. (MGO), muscle lactate 0 min p.m. (MLO), pH in M. longissimus dorsi 45 min p.m. (pH,), carcass hot weight (CW). Moreover, it was calculated the CK change (IOOx (CKE-CKU)/ CKU) during lairage. The CKU and CKE values were Iog l 0 transformed. Statistical analyses Conventional statistical methods were used to calculate means, standard deviations and standard error of the means (SEM). The re- lations between the measured “lairage varia- bles” and porcine stress and meat quality were analysed by simple regression. Moreover, to estimate the influence of lairage on blood CK activity and carcass temperature, a stepwise linear regression analysis was performed (statistical program PATO for microcom- puters, Mikrovuo, Finland). The regression model (1) included the de- pendent variable Yj (i=l—3), the 16 in- dependent variables Xj (j = 1 16, j and the standardized regression coefficients Bj 0 = 1-16, j*i). Yj = B,X, + B 2X 2 + B,X, + . . . + 816B I6X 16 (1) Prediction equations (2) were developed using stepwise regression analysis (Honka- vaara, 1989). Y i = B(l +B,X 1 + B 2X 2 +...+Bn Xn (i = 1 —3, n = 3-5) (2) Results Prediction of porcine stress Table 1 shows the combined effects of stud- ied variables on blood CK activity and carcass temperature during lairage. Thus the coeffi- cient of determination (R 2 X 100)of the predic- tion equations were for the CK change, CK at exsanguination and carcass temperature 87.0 %, 80.5 % and 71.8 %, respectively. The combined effects of the independent variables of the prediction equations are discussed be- low. Lairage temperature In general, temperature of lairage, TL was positively related to external temperature, ET (TL= 15.844 + 0.548ET, R 2 100 = 20 V», p< 0.001). Thus, a I°C increase in external temperature increased lairage temperature by O.6°C. In this study, duration of lairage, DL (DL= 1495.69-67.419TL, R 2 100=19 %, PcO.001) and fast duration, FD (FD = 1583.82—28.224TL, R 2 100= 7 %, PcO.Ol) were reduced by 67 min and 28 min for each degree increase in lairage temperature, re- spectively. Moreover, carcass hot weight, CW was positively related to lairage temperature (CW = 57.322 + 1.148TL, R 2 100= 17 %, P< 0.001) which shows that heavy pigs were slaughtered in warm weather. Furthermore, a I°C increase in lairage temperature decreased serum lactate, SL by 0.4 mmol/1 (SL = 20.022-0.422TL, R 2 100= 6 %, P<0.02) and increased serum pH, SpH by 0.2 pH units (SpH = 7.615+ 0.024TL, R 2 100 =6 %, P<0.02). In addition, increases in external temperature accounted for 60.0 % of the increase in carcass temperature which, on the other hand, accounted for 14.2 °/o of the elevation in CK activity during lairage (Table 1). Thus it was concluded that high ex- ternal and lairage temperature had a detrimen- tal effect on carcass temperature. The collected data were classified into four groups of nearly the same number of pigs ac- cording to the increase in lairage temperature. Table 2 shows the variables that differed sig- nificantly between the groups. At the abattoir, the increase in CK activity was highest at 16°C, whereas this increase was only 82.0 % without reactors. Heat stress elevated blood CK level both during transport and lairage which resulted in a low increase in CK activity in the pigs held at 21 °C. In this group, the prolonged heat stress accounted for the smallest muscle glycogen content and the Table 1. The best stepwise regression models" for predicting porcine stress during lairage. Prediction equationsb R! 100* % Dfd Carcass temperature = 38.609 + 0.801 ET - 0.178HL +0.187MG0 +0.259CK change CK at exsanguination = 194.36+0.514CKU -0.0925 L + 0.756CK change CK change* = - 1000.33 + 0.139CT0 0.677CKU + I.OI6CKE + 0.155 L-0.151 MG„ 71.8 4/45 80.5 3/87 87.0 5/44 “ Regression models have significant F-values (P<0.002). h Abbreviations given in text. 1 Coefficient of determination x 100. d Degrees of freedom. , ,„„ . .CK at exsanguination-CK during unloading CK change (%)= 100 x —-— : ■CK during unloading 427 lowest incidence of PSE. Actually, carcasses of these animals had the slowest pH fall in the LD muscle (Table 2). On the other hand, the occurrence of PSE was highest at 16°C, but it decreased to 8.3 % without reactors. The high PSE frequency at 12°Cmight result from the stressful treatment when pigs were woken up after overnight holding and were driven to stunning. related to external temperature, ET (HL = 51.945 +2.907ET, R 2 100=12%, P<0.002). Thus, a I°C increase in external temperature increased lairage humidity by 2.9 %RH. Fur- thermore, muscle glycogen content, MG 0 was decreased by 0.22 pmol/g for each per cent RH increase in lairage humidity (MGO = 41.099 —0.222HL, R 2 100 = 5 %, P<0.03). However, carcass temperature was poorly described by lairage humidity, as indicated by a low partial R 2 100 of 4.8 % (Table 1).Lairage humidity The collected data were classified into four groups of nearly the same number of pigs ac-Humidity of lairage, HL was positively Table 2. Effect of lairage temperature on blood composition and carcass traits. Means within a row with different superscripts are significantly different (P<0.05). CK change as in table I. Table 3. Effect of lairage humidity on blood composition and carcass traits. Variable Lairage temperature, °C SEM 13 16 18 21 Lairage time, h 13.9“ 4.4 b 4.3b 2.5 b 0.75 Fasting time, h 21.8“ 17.7b 17.9b 18.5b 0.52 CK change11 , % +89.0 +103.0 +75.9 +61.7 21.9 Serum glucose, mmol/1 6.7“ 5.0 6.1 4.4 b 0.05 SErum lactate, » 15.5“ 11.l b 13.3 12.2b 0.06 Serum pH 7.9“ B.o' 7.9“ 8.3b 0.03 Carcass temperature, °C 38.9“ 38.l b 38.81U 39.6'- 0.13 Carcass hot weight, kg 69.4“ 76.5 b 79.5 b 79.6 b 0.79 pH, <5.8, PSE, % 20.8 21.4 15,8 13.3 5.8< pH, <6.4, » 66.7 46.4 47.4 26.7 6.40.05). While the pigs of the lowest humidity of 38 %RH had the slowest pH fall in the LD muscle 45 min p.m., how- ever, these animals had the highest carcass temperature at slaughter. Lairage lime In practice, pigs are slaughtered either on the transport day or after overnight holding. In order to compare the effect of lairage time on porcine stress and meat quality the mate- rial was divided into the two groups shown in Table 4. Thus the pigs of the first group, hold- ing time of 2.4 ±0.9 h, were fed either in the afternoon and were transported in the next morning, or were fed in the morning and were transported in the middle of the day, in any case they were slaughtered on the transport day. Whereas the pigs of the second group, holding timeof 19.012.0 h, were fed at noon of the transport day, and were held overnight at the abattoir before slaughtering. Conse- quently the difference in fasting time was sig- nificant (P< 0.001) between the two groups. In addition, pigs of the short and long hold- ing times were slaughtered, respectively, in the afternoon and in the morning which ac- counted for the difference in lairage temper- ature. In general, serum lactate level, SL was positively related to the duration of lairage, DL (SL= 11.963 + 0.003DL, R 2 100=8 %, P< 0.005). Thus a 60 min increase in holding time increased serum lactate by 0.18 mmol/l. Nevertheless muscle pH, was negatively cor- related (PcO.Ol) with the lairage times of 0.5 h to 22 h, there were differences in this Table 4. Effect of lairage time on blood composition and carcass traits. Variable Slaughtering Sign. SEM T “ level8On trans- After over- port day night lairage Fasting time, h 16.7 24.8 *** 0.52 Lairage temperature, °C 17.1 14.4 *** 0.28 Lairage humidity, % 55.1 55.3 ns 1.18 Log CK during unloading, U/l 3.5 3.3 ns 0.35 Log CK at exsanguination, U/l 3.5 3.6 ns 0.36 Serum glucose, mmol/1 5.0 6.7 ** 0.05 Serum glycerol, » 0.65 0.54 ns 0.003 Serum lactate, » 12.2 15.6 *• 0.06 Serum pH 8.0 8.0 ns 0.03 Carcass temperature, °C 38.4 39.3 ** 0.13 Glycogen of LD, pmol/g 30.2 22.8 •* 0.20 Lactate of LD, » 44.4 47.8 ns 0.13 Carcass hot weight, kg 78.2 70.7 **• 0.79 pH, <5.8, PSE, Vo 14.9 25.0 s.B