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Electrical stunning of lambs: The effect of stunning parameters and drugs affecting blood flow and behaviour on petechial haemorrhage incidence
Meat Science 9 (1983) 247-256
Electrical Stunning of Lambs: The Effect of Stunning Parameters and Drugs Affecting Blood Flow and Behaviour on Petechial Haemorrhage Incidence C. E. Devine, K. V. Gilbert & Sara Ellery Meat Industry Research Institute of New Zealand (Inc.), PO Box 617, Hamilton, New Zealand (Received: 30 June, 1982)
SUMMARY Head-to-back electrical stunning of lambs results in speckle bruising, a kind o f petechial haemorrhage in muscle fascia, especially when the lamb is tightly restrained. Other factors still appear to modify speckle and some of these are int'estigated here. There was a significant increase in leg speckle with long stunning duration or high stunning current, but there was little or no increase.['or the loin. When phenylephrine, a t'asoconstrictor, was administered before stunning, there was a reduced speckle compared with the administration of isoproterenol, a vasodilator. The greatest speckle resulted from high currents and isoproterenol administration. These results are consistent with the view that increased blood at speckle sites, i.e. a blush, during the spasm that takes place during stunning, increases speckle. In lambs tranquillized with valium or excited with adrenaline there was no significant difference in speckle for the legs. There was a significant increase of speckle in the loins of valiumtreated lambs. Although increased peripheral blood flow may increase speckle, the effects of stress such as release of adrenaline may reduce this effect.
INTRODUCTION
Head-to-back
stunning, or modifications such as head-to-foreleg
stunning used in New Zealand lamb processing plants, abolishes blood 247 Meat Science 0309-1740/83/$03-00 ~ Applied Science Publishers Ltd, England, 1983. Printed in Great Britain
248
C. E. Devine, K. V. Gilbert, Sara Ellery
splash and enables a degree of stillness to be achieved for good and safe carcass dressing (Gilbert & Devine, 1982). Petechial haemorrhage, a bruise-type lesion (speckle), which occasionally occurs on loins or rear legs during electrical stunning, is due to carcass movement during stunning, which is more severe when the lamb is held in a restraint such as a V-shaped conveyor (Gilbert & Devine, 1982). Blood pressure rises during stunning do not cause speckle but may exacerbate it. With these factors in mind, several phases of experimentation were undertaken to try to explain other variations in speckle levels. First, the effects of high and low currents and short and long stunning duration on speckle were examined. Secondly, these parameters were investigated in conjunction with a change in blood distribution and flow using vasoconstrictor and vasodilator drugs applied immediately prior to stunning. Thirdly, to determine the effect of excitement on speckle bruising the effects of adrenaline and valium administered prior to stunning were compared.
METHODS Source of lambs and stunning procedures
Lambs from breeding and growth trials, ranging in liveweight from 24 to 40 kg, were slaughtered. They included ewes, wethers or rams under the age of 1 year and were representative of normal breeds used in New Zealand. All lambs were stunned with a head-to-back stunner, the applied open circuit voltage being 400 V with the current limited at selected levels by internal chokes. After stunning the lambs were bled with a thoracic stick by cutting the vena cava and auricles and dressed as normal (Gilbert & Devine, 1982). Blood pressure measurements
Several lambs were cannulated for blood pressure measurements as described previously (Gilbert & Devine, 1982). The following drugs were then injected, via the jugular vein, before stunning, at the dose level required to obtain an appropriate response for the much larger series below in which blood pressures were not obtained: DL isoproterenol
Electrical stunning of lambs
249
hydrochloride (Sigma Chemical Co., Missouri) 0"5 mg in 5 ml per lamb (two lambs): phenylephrine hydrochloride (Sterling Pharmaceuticals (NZ) Ltd) 0"5 mg in 5 ml per lamb (two lambs). Current, duration of stunning and treatment with phenylephrine and isoproterenol The actual voltage used for stunning was adjusted so that the following nominal current and time sequences were followed: (a) 68 lambs, 1.5 A for 4 s (standard stun); (b) 68 lambs, 1-5 A for 2 s (short stun), (c) 67 lambs, 1-5 A for 10s (long stun), (d) 69 lambs, 0.7A for 4s (low current). The individual current values were recorded and averaged. Drugs were injected as follows where appropriate. Lambs were shorn in the neck region and a needle inserted through the skin into the jugular vein. The drug was then injected over a 20 s period via the jugular vein with the vasoconstrictor phenylephrine hydrochloride (69 lambs, 0.5 mg in 2ml per lamb) or the vasodilator isoproterenol hydrochloride (69 lambs, 0-5 mg in 2 ml per lamb) 2 min before stunning. Two additional treatments were included: phenylephrine administration and a long stun time of 10 s (66 lambs) and isoproterenol administration with a low stun current (68 lambs). There were eight treatments, each containing approximately 68 lambs, combining drug injection, stunning time, and stunning current, randomly carried out on 544 lambs. The same operator stunned all animals. Treatment with adrenaline and valium There were three treatments in this group of 169 lambs as follows. (a) Control lambs (n = 60) stunned as above for 4 s at 1-5 A, (b)lambs (n = 54) tranquillized with an intravenous injection via the jugular vein of 5 mg of diazepam (Valium, Roche Products, Auckland, New Zealand) administered in 2 ml, 3 h before stunning and (c) lambs (n = 55) injected with 0-5mg of adrenaline (McGraw Ethicals Ltd, Auckland, New Zealand) administered in 2 ml over 20 s, two minutes before stunning as above. Speckle For all experiments, severity of speckle for each lamb was measured after
250
C. E, Devine, K. V. Gilbert, Sara Ellery
removal of the superficial fat from the appropriate areas, on a 0 - 5 scale (0 score, no speckle, to a 5 score which indicates large fiery red areas). In the statistical analysis, the speckle scores were grouped: a trace of speckle included scores of 1 and 2 and severe included, 3, 4 and 5. The sites examined were the muscle fascia of Biceps femoris (BF), Semimembranosus (SM) and Semitendinosus (ST) and the surface fat of the TABLE 1 T h e Significance o f the Eight T r e a t m e n t s (n ~ 68 for E a c h T r e a t m e n t ) o n S p e c k l e I n c i d e n c e A f t e r H e a d - t o - B a c k S t u n n i n g for the S M , ST, B F a n d Loin M u s c l e s ( P h e n y l e p h r i n e (0-5 mg) a n d i s o p r o t e r e n o l (0.5 mg) were e a c h a d m i n i s t e r e d 2 min p r i o r to s t u n n i n g . S t u n n i n g times are 2 s for the s h o r t s t u n , 10 s for the long stun a n d 4 s for t h e s t a n d a r d stun. T h e low c u r r e n t is 0-64 A a n d the high c u r r e n t is 1.37 A)
Treatment
L o n g s t u n versus s h o r t s t u n High c u r r e n t versus low c u r r e n t Isoproterenol--high current versus low c u r r e n t Phenylephrine--long stun versus s h o r t stun Phenylephrine-isoproterenol Batch difference Significance o f t r e a t m e n t
Muscles SM
ST
BF
Loin
* **
** **
* NS
NS NS
**
**
*
*
** * *** ***
* * *** ***
* * ** ***
* * *** *
* P < 0"05.
** P < 0 - 0 1 . *** P < 0-001. N S = N o t significant.
loin (Gilbert & Devine, 1982). The results of these trials can be expressed as a severity or as an incidence. The severity is most easily determined from the Figures, in which the percentage speckle, displayed in graphical form, has been grouped into none, trace and severe for the loin and SM muscle. The percentage of severe speckle gives a relative idea of the effectiveness of the treatment. The speckle incidence for loin, SM, ST and BF was analysed statistically (Table 1) using generalized linear models (GLIM) (Nelder & Wedderburn, 1972) to average out the batch effects (day to day variation).
Electrical stunning of lambs
25 i
RESULTS Blood pressure and the effect of phenylephrine and isoproterenol The resting blood pressure before injection ranged from 90 to 130mm Hg. Following injection of the vasoconstrictor phenylephrine, there was a rise in blood pressure to 265 m m Hg. Upon head-to-back stunning the pressure rose further to 305 mm Hg during stunning and then fell to approximately 50 m m Hg as in normal head-to-back stunning (Gilbert & Devine, 1982). With injection of the vasodilator isoproterenol there was a small initial rise in pressure of 10 mm Hg, followed by a fall in pressure to 80 mm Hg. Upon head-to-back stunning, the pressure rose to 103 mm Hg during stunning, then fell in a similar pattern as in normal head-to-back stunning. The effects of both drugs persisted for the 2 min period prior to stunning. The movement of the lambs following stunning was not detectably modified by either drug. Effects of phenylephrine, isoproterenol, current level and duration of stunning on speckle There were eight treatments encompassing the drug administration and electrical effects. Statistical analysis of the speckle incidence shown in Table l indicated that there were significant differences between treatments. The difference between treatment days (i.e. batch difference) (P < 0.001) was greater than the individual treatment difference in all cases. On all leg muscles speckle increased significantly at long stunning times with high stunning currents. There was little or no significant difference in loin speckle with variations in current or stunning duration. There was a significant difference in the results obtained by isoproterenol and phenylephrine administration for both legs and loins. The greatest speckle increase occurred as a result of high current with isoproterenol administration. Reduction of speckle due to phenylephrine administration was less than that possible by lowering the current or reducing duration of stunning (Table 1). Due to the batch differences, the severity of speckle did not show any significant treatment effect, but trends are seen in the bar graphs (Figs 1 and 2). Speckle severity for the loin was only slightly increased with long
252
C. E. Devine, K. V. Gilbert, Sara Ellery A.
S h o r t Vs Long S t u n With High Current.
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Fig. 1. Severity of speckle in loins and legs of lambs stunned with a head-to-back stunner. In this and the following Figures, a trace corresponds to a speckle .score of I and 2 and severe speckle corresponds to speckle scores of 3, 4 and 5. Values less than 10 are not displayed. For convenience, the speckle scores are for the loin and SM muscle only. A. Short stun of 2 s versus a long stun of 10 s. B. Standard stun time of 4 s with low (0.64A) and high currents (1-35A).
s t u n n i n g times a n d high s t u n n i n g c u r r e n t b u t there was a d r a m a t i c increase in speckle severity for the legs (Fig. IA a n d IB). In the p h e n y l e p h r i n e - t r e a t e d lambs, there was a lower severity o f speckle in legs a n d loins (Fig. 2B) c o m p a r e d with s t a n d a r d s t u n n i n g in the absence o f t r e a t m e n t (Fig. IB). W h e n the c u r r e n t d u r a t i o n was 10s c o m p a r e d with the s t a n d a r d s t u n n i n g time o f 4 s speckle severity increased for b o t h loins a n d legs. In the i s o p r o t e r e n o l - t r e a t e d lambs there was a m u c h increased severity o f speckle in the legs and loins (Fig. 2A) c o m p a r e d with the s t a n d a r d stun a l o n e (Fig. I B). W h e n the s t u n n i n g c u r r e n t was lowered, severity o f speckle o n legs a n d loins was r e d u c e d in the presence o f the d r u g (Fig. 2A).
Electrical stunnbtg of lambs
253
A. Std Time, Isoproterenol, High Vs Low Current.
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Fig. 2. Severity of speckle in loins and legs of lambs injected with drugs and then stunned with a head-to-back stunner 120s later. The doses are the same as Table l A. Administration via the jugular vein of isoproterenol (0-5 rag/lamb), 2 rain prior to stunning for 4s with either high or low currents. B. Administration via the jugular vein of phenylephrine (0.5 rag/lamb), 2 rain prior to stunning with a standard stun (4 s, 1.0 A), or a long duration stun of 10s.
Anxiety state and speckle The four mobs of animals used in this study were different from those for the phenylephrine and isoproterenol studies and the control speckle levels are accordingly different. In Fig. 3, the leg and loin speckle severity shown in the bar graphs, is slightly higher in the valium- and adrenaline-treated than in the control group with the valium-treated group being highest. Statistical analysis of speckle incidence showed a significant increase in the loin only for the valium treatment (P < 0"05). Batch differences in speckle The most interesting consistent observations for the electrical and drug
254
C. E. Devine, K. V. Gilbert, Sara Ellery
An.r/eLy StaLe ~" Speckle Bruising in Lamb. ~"2.6
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Fig. 3. Severityof speckle in loins and legs of lambs stunned with a head-to-back stun of 4s duration at 1-35A. The lambs were either untreated (n = 60), or injected via the jugular vein with the tranquillizer diazepam (Valium 5 rag/lamb) 3 h before stunning n = 54 or excited with adrenaline injection via the jugular vein (0.5 mg/lamb) 5 min before stunning (n = 55). treatments was the significant batch difference, i.e. day to day variation (a total of seven batches), overshadowing any single treatment difference although there was an overall significant treatment effect (Table 1). In the case of the anxiety state trial, there were four batches showing a significant batch difference. The treatment effect was only significant for the valium administration.
DISCUSSION With head-to-back stunning the electrical parameters of higher current and longer stunning duration increased speckle severity and incidence for the legs, but there was no significant difference for the loin. The reason for little change in the loin probably lies in the fact that the head-to-back electrode placement always ensures a maximal tetanic effect over the whole musculature of the loin, overriding most variations of stunning duration, current level or interaction with the vasoactive drugs phenylephrine and isoproterenol. As the legs are not directly stimulated but are affected only through the nervous system, there are modifications of speckle in this case. The high current most likely produces its effect through a violent muscle spasm at the onset of stunning, but the reason for increased speckle levels associated with long stunning is not so clear. It
Electrical stunning of lambs
255
may be related to the muscle tension producing local high pressure regions in the vascular system to force blood out over a longer time from vessels which had ruptured during the muscle spasm. In effect, the speckle initiation is the same, but its expression is worse. In a practical situation, high currents are often used because it is assumed that animal stillness is improved. Improperly positioned stunning electrodes could result in poor stunning, but this should not be used as an excuse to turn up the stunning current as increased levels of speck!e could result. The vasoconstrictor responses of phenylephrine and the vasodilator responses of isoproterenol are termed ~- and /~-adrenergic responses respectively (Goodman & Gilman, 1970). Interpretation of the decreased speckle with vasoconstrictor drugs and the increased speckle with vasodilator drugs and a further increase with high current and long stunning time is consistent with the view that an increase of blood at the sensitive sites on the muscle fascia, i.e. creating a blush, results in an increase in speckle. One of the effects of vasodilation is to increase blood flow in peripheral blood vessels, and mimic a condition that could be produced during overheating. Whether temperature-induced effects are really mimicked by vasodilation has yet to be tested. Such situations may be counteracted in practice by vasoconstrictor actions of adrenaline produced during other forms of stress. In lambs environmental stress such as transport and washing normally release adrenaline into the blood from the adrenal medulla (Pearson, 1979). Although adrenaline produces both =- and /~-responses, the c~response, i.e. vasoconstrictor response similar to that of phenylephrine, predominates at the speckle sites. Even coupled with the associated increase in blood pressure, there is no significant difference in speckle for the adrenaline-treated group compared with the untreated group. It appears that adrenaline released during stress has virtually no effect on speckle levels, indicating that fear or agitation do not increase speckle levels. Conversely, it seems that the tranquillizer valium rather than protecting lambs against speckle actually increases speckle slightly in the loin. One of the puzzling features of this study is that the batch difference seems to have a more profound effect than any treatment which was given such as high and low current, short and long stunning times, vasoconstrictors, vasodilators, adrenaline or valium. The day-to-day variation in speckle is unexplained. How on-farm factors or subtle variations in weather can affect speckle is not clear. It would seem that
256
c. E. Devine, K. V. Gilbert, Sara Ellery
apparently obvious modifiers such as "stress" or high temperatures have little real effect. One factor that was not determined was wool length, which, in retrospect, might have affected the way the lambs were held in the restrain conveyor and thus modify the movement of the lambs upon stunning. Although individual treatments had only moderate significance in some cases in affecting speckle levels, there was a very significant treatment effect, suggesting that there are several subtly interacting factors.
ACKNOWLEDGEMENTS We wish to acknowledge the help of Mr H. H. Bishop for surgery, Mr D. Duganzich for statistical advice, Mr John Dobbie for making the lambs available and the slaughtermen, all of Ruakura Agricultural Research Centre, Hamilton. We are also indebted to Mr R. Hand for equipment design and modifications, Mr A. Graafhuis, Mr R. Blunt, Margaret Snodgrass, Carole Pope and Sharon Averill for other technical help.
REFERENCES Gilbert, K. V. & Devine, C. E. (1982). Meat Science, 7(3), 197. Goodman, L. S. & Gilman, A. (1970). The pharmacological basis of therapeutics (4th cdn). The Macmillan Co., New York. Nelder, J. A, & Wedderburn, R. W, M. (1972). J.R. Statist. Soc. A, 135, 370. Pearson, A. J. (1979). Catechohnine physiology in the sheep. PhD Thesis, University of Waikato, Hamilton, New Zealand.
Electrical Stunning of Lambs: The Effect of Stunning Parameters and Drugs Affecting Blood Flow and Behaviour on Petechial Haemorrhage Incidence C. E. Devine, K. V. Gilbert & Sara Ellery Meat Industry Research Institute of New Zealand (Inc.), PO Box 617, Hamilton, New Zealand (Received: 30 June, 1982)
SUMMARY Head-to-back electrical stunning of lambs results in speckle bruising, a kind o f petechial haemorrhage in muscle fascia, especially when the lamb is tightly restrained. Other factors still appear to modify speckle and some of these are int'estigated here. There was a significant increase in leg speckle with long stunning duration or high stunning current, but there was little or no increase.['or the loin. When phenylephrine, a t'asoconstrictor, was administered before stunning, there was a reduced speckle compared with the administration of isoproterenol, a vasodilator. The greatest speckle resulted from high currents and isoproterenol administration. These results are consistent with the view that increased blood at speckle sites, i.e. a blush, during the spasm that takes place during stunning, increases speckle. In lambs tranquillized with valium or excited with adrenaline there was no significant difference in speckle for the legs. There was a significant increase of speckle in the loins of valiumtreated lambs. Although increased peripheral blood flow may increase speckle, the effects of stress such as release of adrenaline may reduce this effect.
INTRODUCTION
Head-to-back
stunning, or modifications such as head-to-foreleg
stunning used in New Zealand lamb processing plants, abolishes blood 247 Meat Science 0309-1740/83/$03-00 ~ Applied Science Publishers Ltd, England, 1983. Printed in Great Britain
248
C. E. Devine, K. V. Gilbert, Sara Ellery
splash and enables a degree of stillness to be achieved for good and safe carcass dressing (Gilbert & Devine, 1982). Petechial haemorrhage, a bruise-type lesion (speckle), which occasionally occurs on loins or rear legs during electrical stunning, is due to carcass movement during stunning, which is more severe when the lamb is held in a restraint such as a V-shaped conveyor (Gilbert & Devine, 1982). Blood pressure rises during stunning do not cause speckle but may exacerbate it. With these factors in mind, several phases of experimentation were undertaken to try to explain other variations in speckle levels. First, the effects of high and low currents and short and long stunning duration on speckle were examined. Secondly, these parameters were investigated in conjunction with a change in blood distribution and flow using vasoconstrictor and vasodilator drugs applied immediately prior to stunning. Thirdly, to determine the effect of excitement on speckle bruising the effects of adrenaline and valium administered prior to stunning were compared.
METHODS Source of lambs and stunning procedures
Lambs from breeding and growth trials, ranging in liveweight from 24 to 40 kg, were slaughtered. They included ewes, wethers or rams under the age of 1 year and were representative of normal breeds used in New Zealand. All lambs were stunned with a head-to-back stunner, the applied open circuit voltage being 400 V with the current limited at selected levels by internal chokes. After stunning the lambs were bled with a thoracic stick by cutting the vena cava and auricles and dressed as normal (Gilbert & Devine, 1982). Blood pressure measurements
Several lambs were cannulated for blood pressure measurements as described previously (Gilbert & Devine, 1982). The following drugs were then injected, via the jugular vein, before stunning, at the dose level required to obtain an appropriate response for the much larger series below in which blood pressures were not obtained: DL isoproterenol
Electrical stunning of lambs
249
hydrochloride (Sigma Chemical Co., Missouri) 0"5 mg in 5 ml per lamb (two lambs): phenylephrine hydrochloride (Sterling Pharmaceuticals (NZ) Ltd) 0"5 mg in 5 ml per lamb (two lambs). Current, duration of stunning and treatment with phenylephrine and isoproterenol The actual voltage used for stunning was adjusted so that the following nominal current and time sequences were followed: (a) 68 lambs, 1.5 A for 4 s (standard stun); (b) 68 lambs, 1-5 A for 2 s (short stun), (c) 67 lambs, 1-5 A for 10s (long stun), (d) 69 lambs, 0.7A for 4s (low current). The individual current values were recorded and averaged. Drugs were injected as follows where appropriate. Lambs were shorn in the neck region and a needle inserted through the skin into the jugular vein. The drug was then injected over a 20 s period via the jugular vein with the vasoconstrictor phenylephrine hydrochloride (69 lambs, 0.5 mg in 2ml per lamb) or the vasodilator isoproterenol hydrochloride (69 lambs, 0-5 mg in 2 ml per lamb) 2 min before stunning. Two additional treatments were included: phenylephrine administration and a long stun time of 10 s (66 lambs) and isoproterenol administration with a low stun current (68 lambs). There were eight treatments, each containing approximately 68 lambs, combining drug injection, stunning time, and stunning current, randomly carried out on 544 lambs. The same operator stunned all animals. Treatment with adrenaline and valium There were three treatments in this group of 169 lambs as follows. (a) Control lambs (n = 60) stunned as above for 4 s at 1-5 A, (b)lambs (n = 54) tranquillized with an intravenous injection via the jugular vein of 5 mg of diazepam (Valium, Roche Products, Auckland, New Zealand) administered in 2 ml, 3 h before stunning and (c) lambs (n = 55) injected with 0-5mg of adrenaline (McGraw Ethicals Ltd, Auckland, New Zealand) administered in 2 ml over 20 s, two minutes before stunning as above. Speckle For all experiments, severity of speckle for each lamb was measured after
250
C. E, Devine, K. V. Gilbert, Sara Ellery
removal of the superficial fat from the appropriate areas, on a 0 - 5 scale (0 score, no speckle, to a 5 score which indicates large fiery red areas). In the statistical analysis, the speckle scores were grouped: a trace of speckle included scores of 1 and 2 and severe included, 3, 4 and 5. The sites examined were the muscle fascia of Biceps femoris (BF), Semimembranosus (SM) and Semitendinosus (ST) and the surface fat of the TABLE 1 T h e Significance o f the Eight T r e a t m e n t s (n ~ 68 for E a c h T r e a t m e n t ) o n S p e c k l e I n c i d e n c e A f t e r H e a d - t o - B a c k S t u n n i n g for the S M , ST, B F a n d Loin M u s c l e s ( P h e n y l e p h r i n e (0-5 mg) a n d i s o p r o t e r e n o l (0.5 mg) were e a c h a d m i n i s t e r e d 2 min p r i o r to s t u n n i n g . S t u n n i n g times are 2 s for the s h o r t s t u n , 10 s for the long stun a n d 4 s for t h e s t a n d a r d stun. T h e low c u r r e n t is 0-64 A a n d the high c u r r e n t is 1.37 A)
Treatment
L o n g s t u n versus s h o r t s t u n High c u r r e n t versus low c u r r e n t Isoproterenol--high current versus low c u r r e n t Phenylephrine--long stun versus s h o r t stun Phenylephrine-isoproterenol Batch difference Significance o f t r e a t m e n t
Muscles SM
ST
BF
Loin
* **
** **
* NS
NS NS
**
**
*
*
** * *** ***
* * *** ***
* * ** ***
* * *** *
* P < 0"05.
** P < 0 - 0 1 . *** P < 0-001. N S = N o t significant.
loin (Gilbert & Devine, 1982). The results of these trials can be expressed as a severity or as an incidence. The severity is most easily determined from the Figures, in which the percentage speckle, displayed in graphical form, has been grouped into none, trace and severe for the loin and SM muscle. The percentage of severe speckle gives a relative idea of the effectiveness of the treatment. The speckle incidence for loin, SM, ST and BF was analysed statistically (Table 1) using generalized linear models (GLIM) (Nelder & Wedderburn, 1972) to average out the batch effects (day to day variation).
Electrical stunning of lambs
25 i
RESULTS Blood pressure and the effect of phenylephrine and isoproterenol The resting blood pressure before injection ranged from 90 to 130mm Hg. Following injection of the vasoconstrictor phenylephrine, there was a rise in blood pressure to 265 m m Hg. Upon head-to-back stunning the pressure rose further to 305 mm Hg during stunning and then fell to approximately 50 m m Hg as in normal head-to-back stunning (Gilbert & Devine, 1982). With injection of the vasodilator isoproterenol there was a small initial rise in pressure of 10 mm Hg, followed by a fall in pressure to 80 mm Hg. Upon head-to-back stunning, the pressure rose to 103 mm Hg during stunning, then fell in a similar pattern as in normal head-to-back stunning. The effects of both drugs persisted for the 2 min period prior to stunning. The movement of the lambs following stunning was not detectably modified by either drug. Effects of phenylephrine, isoproterenol, current level and duration of stunning on speckle There were eight treatments encompassing the drug administration and electrical effects. Statistical analysis of the speckle incidence shown in Table l indicated that there were significant differences between treatments. The difference between treatment days (i.e. batch difference) (P < 0.001) was greater than the individual treatment difference in all cases. On all leg muscles speckle increased significantly at long stunning times with high stunning currents. There was little or no significant difference in loin speckle with variations in current or stunning duration. There was a significant difference in the results obtained by isoproterenol and phenylephrine administration for both legs and loins. The greatest speckle increase occurred as a result of high current with isoproterenol administration. Reduction of speckle due to phenylephrine administration was less than that possible by lowering the current or reducing duration of stunning (Table 1). Due to the batch differences, the severity of speckle did not show any significant treatment effect, but trends are seen in the bar graphs (Figs 1 and 2). Speckle severity for the loin was only slightly increased with long
252
C. E. Devine, K. V. Gilbert, Sara Ellery A.
S h o r t Vs Long S t u n With High Current.
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Fig. 1. Severity of speckle in loins and legs of lambs stunned with a head-to-back stunner. In this and the following Figures, a trace corresponds to a speckle .score of I and 2 and severe speckle corresponds to speckle scores of 3, 4 and 5. Values less than 10 are not displayed. For convenience, the speckle scores are for the loin and SM muscle only. A. Short stun of 2 s versus a long stun of 10 s. B. Standard stun time of 4 s with low (0.64A) and high currents (1-35A).
s t u n n i n g times a n d high s t u n n i n g c u r r e n t b u t there was a d r a m a t i c increase in speckle severity for the legs (Fig. IA a n d IB). In the p h e n y l e p h r i n e - t r e a t e d lambs, there was a lower severity o f speckle in legs a n d loins (Fig. 2B) c o m p a r e d with s t a n d a r d s t u n n i n g in the absence o f t r e a t m e n t (Fig. IB). W h e n the c u r r e n t d u r a t i o n was 10s c o m p a r e d with the s t a n d a r d s t u n n i n g time o f 4 s speckle severity increased for b o t h loins a n d legs. In the i s o p r o t e r e n o l - t r e a t e d lambs there was a m u c h increased severity o f speckle in the legs and loins (Fig. 2A) c o m p a r e d with the s t a n d a r d stun a l o n e (Fig. I B). W h e n the s t u n n i n g c u r r e n t was lowered, severity o f speckle o n legs a n d loins was r e d u c e d in the presence o f the d r u g (Fig. 2A).
Electrical stunnbtg of lambs
253
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Fig. 2. Severity of speckle in loins and legs of lambs injected with drugs and then stunned with a head-to-back stunner 120s later. The doses are the same as Table l A. Administration via the jugular vein of isoproterenol (0-5 rag/lamb), 2 rain prior to stunning for 4s with either high or low currents. B. Administration via the jugular vein of phenylephrine (0.5 rag/lamb), 2 rain prior to stunning with a standard stun (4 s, 1.0 A), or a long duration stun of 10s.
Anxiety state and speckle The four mobs of animals used in this study were different from those for the phenylephrine and isoproterenol studies and the control speckle levels are accordingly different. In Fig. 3, the leg and loin speckle severity shown in the bar graphs, is slightly higher in the valium- and adrenaline-treated than in the control group with the valium-treated group being highest. Statistical analysis of speckle incidence showed a significant increase in the loin only for the valium treatment (P < 0"05). Batch differences in speckle The most interesting consistent observations for the electrical and drug
254
C. E. Devine, K. V. Gilbert, Sara Ellery
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Fig. 3. Severityof speckle in loins and legs of lambs stunned with a head-to-back stun of 4s duration at 1-35A. The lambs were either untreated (n = 60), or injected via the jugular vein with the tranquillizer diazepam (Valium 5 rag/lamb) 3 h before stunning n = 54 or excited with adrenaline injection via the jugular vein (0.5 mg/lamb) 5 min before stunning (n = 55). treatments was the significant batch difference, i.e. day to day variation (a total of seven batches), overshadowing any single treatment difference although there was an overall significant treatment effect (Table 1). In the case of the anxiety state trial, there were four batches showing a significant batch difference. The treatment effect was only significant for the valium administration.
DISCUSSION With head-to-back stunning the electrical parameters of higher current and longer stunning duration increased speckle severity and incidence for the legs, but there was no significant difference for the loin. The reason for little change in the loin probably lies in the fact that the head-to-back electrode placement always ensures a maximal tetanic effect over the whole musculature of the loin, overriding most variations of stunning duration, current level or interaction with the vasoactive drugs phenylephrine and isoproterenol. As the legs are not directly stimulated but are affected only through the nervous system, there are modifications of speckle in this case. The high current most likely produces its effect through a violent muscle spasm at the onset of stunning, but the reason for increased speckle levels associated with long stunning is not so clear. It
Electrical stunning of lambs
255
may be related to the muscle tension producing local high pressure regions in the vascular system to force blood out over a longer time from vessels which had ruptured during the muscle spasm. In effect, the speckle initiation is the same, but its expression is worse. In a practical situation, high currents are often used because it is assumed that animal stillness is improved. Improperly positioned stunning electrodes could result in poor stunning, but this should not be used as an excuse to turn up the stunning current as increased levels of speck!e could result. The vasoconstrictor responses of phenylephrine and the vasodilator responses of isoproterenol are termed ~- and /~-adrenergic responses respectively (Goodman & Gilman, 1970). Interpretation of the decreased speckle with vasoconstrictor drugs and the increased speckle with vasodilator drugs and a further increase with high current and long stunning time is consistent with the view that an increase of blood at the sensitive sites on the muscle fascia, i.e. creating a blush, results in an increase in speckle. One of the effects of vasodilation is to increase blood flow in peripheral blood vessels, and mimic a condition that could be produced during overheating. Whether temperature-induced effects are really mimicked by vasodilation has yet to be tested. Such situations may be counteracted in practice by vasoconstrictor actions of adrenaline produced during other forms of stress. In lambs environmental stress such as transport and washing normally release adrenaline into the blood from the adrenal medulla (Pearson, 1979). Although adrenaline produces both =- and /~-responses, the c~response, i.e. vasoconstrictor response similar to that of phenylephrine, predominates at the speckle sites. Even coupled with the associated increase in blood pressure, there is no significant difference in speckle for the adrenaline-treated group compared with the untreated group. It appears that adrenaline released during stress has virtually no effect on speckle levels, indicating that fear or agitation do not increase speckle levels. Conversely, it seems that the tranquillizer valium rather than protecting lambs against speckle actually increases speckle slightly in the loin. One of the puzzling features of this study is that the batch difference seems to have a more profound effect than any treatment which was given such as high and low current, short and long stunning times, vasoconstrictors, vasodilators, adrenaline or valium. The day-to-day variation in speckle is unexplained. How on-farm factors or subtle variations in weather can affect speckle is not clear. It would seem that
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c. E. Devine, K. V. Gilbert, Sara Ellery
apparently obvious modifiers such as "stress" or high temperatures have little real effect. One factor that was not determined was wool length, which, in retrospect, might have affected the way the lambs were held in the restrain conveyor and thus modify the movement of the lambs upon stunning. Although individual treatments had only moderate significance in some cases in affecting speckle levels, there was a very significant treatment effect, suggesting that there are several subtly interacting factors.
ACKNOWLEDGEMENTS We wish to acknowledge the help of Mr H. H. Bishop for surgery, Mr D. Duganzich for statistical advice, Mr John Dobbie for making the lambs available and the slaughtermen, all of Ruakura Agricultural Research Centre, Hamilton. We are also indebted to Mr R. Hand for equipment design and modifications, Mr A. Graafhuis, Mr R. Blunt, Margaret Snodgrass, Carole Pope and Sharon Averill for other technical help.
REFERENCES Gilbert, K. V. & Devine, C. E. (1982). Meat Science, 7(3), 197. Goodman, L. S. & Gilman, A. (1970). The pharmacological basis of therapeutics (4th cdn). The Macmillan Co., New York. Nelder, J. A, & Wedderburn, R. W, M. (1972). J.R. Statist. Soc. A, 135, 370. Pearson, A. J. (1979). Catechohnine physiology in the sheep. PhD Thesis, University of Waikato, Hamilton, New Zealand.