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Aversion of sheep to electro-immobilization and physical restraint
Applied Animal Behaviour Science, 15 (1986) 315--324
315
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
AVERSION OF SHEEP TO ELECTRO-IMMOBILIZATION PHYSICAL RESTRAINT
AND
J. RUSHEN 1
School of Agriculture and Forestry, University of Melbourne, Parkville, Vic. 3052 (Australia) (Accepted for publication 28 February 1986)
ABSTRACT Rushen, J., 1986. Aversion of sheep to electro-immobilization and physical restraint. Appl. Anim. Behav. Sci., 15: 315--324. Thirty-six Merino wethers were forced along a sheep race and were either electroimmobilized using a commercially-available instrument, restrained with the electroimmobilizer electrodes attached, physically restrained in a sheep-handling machine or allowed to run freely through the race. The degree of aversion shown to the place where the treatment occurred was measured by the time taken by the sheep to run through the race on a subsequent occasion ("transit time") and the push-up time required. All forms of restraint increased the push-up and transit times. Sheep that had been electro-immobilized had a greater average transit time after four treatments and a greater average push-up time after two treatments than sheep that were physically restrained, with or without the electrodes attached. These results suggest that sheep find electro-immobilization more aversive than physical restraint. Push-up time was increased if a high current was used, but was unrelated to the duration of electro-immobilization (up to 3 rain). Increasing the current increased the time required by the sheep to recover breathing, which was strongly and positively related to subsequent push-up time. The degree of aversion shown decreases with experience of electro-immobilization.
INTRODUCTION The effects of routine veterinary and animal husbandry procedures on t h e w e l f a r e o f d o m e s t i c a n i m a l s is i n c r e a s i n g l y e n g a g i n g t h e a t t e n t i o n o f v e t e r i n a r y a n d a n i m a l s c i e n t i s t s in m o s t w e s t e r n c o u n t r i e s (e.g. S m i t h , 1983; Fox, 1984). In Australia, the development of fully automated systems f o r s h e a r i n g s h e e p (e.g. H u d s o n , 1 9 8 2 ) m a y h a v e t h e p o t e n t i a l t o i n c r e a s e the degree of stress to which large numbers of animals are routinely exp o s e d . O f p a r t i c u l a r i n t e r e s t is t h e p r o p o s e d u s e o f p u l s e d , l o w - v o l t a g e electric current to immobilize animals, particularly sheep, by producing 1Present address: Animal Research Centre, Agriculture Canada, Ottawa, Ont. K I A 0C6, Canada. 0168-1591/86/$03.50
© 1986 Elsevier Science Publishers B.V.
316
a degree o f involuntary contraction o f the skeletal muscles (Baxter, 1982). An instrument that does this is commercially available 1, and it has been p r o m o t e d by some veterinarians as a useful tool in reducing the stress associated with the physical restraint of cattle. However, Carter et al. (1983) express their belief t hat cattle may find such electro-immobilization to be an unpleasant experience. However, this was a largely subjective judgement. An investigation of the effect that any procedure used in handling animals has on their welfare should include an assessment of the animal's own experience of that procedure. The challenge is to find an objectively measurable parameter (physiological or behavioural) that has a defendable theoretical link with an animal's experiences, and which can therefore be used to make inferences a bout the animal's subjective state while undergoing the treatment. One view o f the function of subjective experiences is to consider them as being instrumental in modifying future behaviour so that situations that are experienced as unpleasant can be avoided in the future. By this logic, if a sheep finds electro-immobilization aversive or unpleasant, it will tend to avoid the place where it has been previously immobilized. This can be quantified by measuring any increase in the time required to move the animal through a race. This measure has been shown to be sensitive to a variety of aversive and rewarding treatments (Hutson, 1982, 1985). EXPERIMENT 1 This ex p er imen t examined the following points: (1) if sheep f o u n d electro-immobilization aversive: (2) wh eth er it was more or less aversive than physical restraint; (3) if sheep r e m e m b e r e d the experience over a period of several months; (4) wh eth er prior experience of electro-immobilization increased or decreased its aversiveness.
Method Thirty-six 3--6-year-old unshorn Merino wethers (35--60 kg liveweight), with no observable physical disabilities, were selected. All had experience o f f r eq u en t h u m a n cont act and handling, but none had previously been electro-immobilized. The sheep were allotted to four t r e a t m e n t groups. This was achieved by running the flock through a race, taking the first four sheep to run t hr ough and allotting one to each group. This was repeated for the n ex t group of four, and so on. The sheep were then marked according to the t r e a t m e n t group to which t hey had been allocated, and the flock was re-assembled. i Feenix Stockstill ®, Feenix International Pty. Ltd., Tarlee, S.A. 5411, Australia.
317 Individual sheep were taken f r om the group n o t in any fixed order but simply according to how easy t h e y were to catch. Each was placed at the head o f a 7-m-long race at the end of which was a " M o f f a t - - V i r t u e " sheephandling machine. This machine consists of two "jaws" that are hinged at the b o t t o m . As the sheep runs between the jaws these can be pulled t o g eth er so as to catch the sheep and hold it in an upright position. The race was divided into four sections and the sheep was allowed a m a x i m u m time o f 2 min to run through each section. The experi m ent er stood at the head o f the race and, once this time had elapsed, moved towards the animal, pushing it if necessary, until it entered the n e x t section. As far as possible, a standard force was applied to the animal. The total time required to run through the race ("transit t i m e " ) and the total time spent moving toward and pushing the sheep ("push-up t i m e " ) were recorded. On the first day, sheep were allowed to run freely through the race six times to allow th e m to become accustomed to it. On the second day, the sheep were subjected to one of f our treatments depending on which group t h e y had previously been allotted to. Ca) Free-running (n = 6). Sheep were allowed to run freely through the race and into a catching pen. (b) Physical restraint (n = 10). After running through the race, the animals were immediately caught and restrained in an upright position in the sheep handling machine for 2.5 min. (c) Full electro-immobilization in = 10). After running through the race and being caught in the sheep-handling machine, the animals were electro-immobilized using a commercially available hand-held Feenix Stockstill electro-immobilizer (see Research Note at the end of this paper). A p p r o x i m a t e l y 30 s after catching the sheep, a needle electrode was inserted under the skin at the base of the tail, and an alligator-clip electrode was placed on the inside o f the contralateral cheek. A maxim u m current of 40--60 mA was initially applied. This was immediately reduced until the animal started breathing and was then gradually increased. The final level was chosen so as to allow regular breathing and in all cases was between 30 and 50 mA. No animal was k e p t witho u t breathing for longer than 15 s. (d) Wired-up (n = 10). The animals were restrained in the handler for 2.5 min with the immobilizer electrodes attached in the manner described above. The current was not t ur ne d on. The procedure was repeated 4 h later, and then twice a day for the next 3 days. On the final day, the animals were timed running through the race a third time, but no t r e a t m e n t was applied. Twelve weeks after the conclusion o f this study, the sheep from the wired-up group and from the electro-immobilized group were run through the race again and timed. In order to de t e r m i ne if prior experience of electro-immobilization alters aversiveness, a second group of 20 newly shorn merino wethers with no previous experience o f electro-immobilization were selected. Ten of
318
the animals were immobilized in the manner described above once a day for 2 consecutive days in a small cage quite separate from the race system. The 10 remaining sheep were restrained in the same cage for 2 min with the electrodes attached, but the current was n o t turned on. This was also done once a day for 2 days. Seventy-two hours later, all animals were run through the race described in the previous experiment and electro-immobilized in the standard manner. This was repeated twice more over 2 days. Transit time and push-up time following the third immobilization were recorded. Results Figure 1 shows the average transit time and Fig. 2 shows the average push-up time for the four groups of sheep for the six trials prior to treatment and for the eight trials after each treatment. 400 []
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Fig. 1. Mean transit time for the four groups o f sheep on each trial (E-I = electro-imm o b i l i z a t i o n ) . Trial 0 represents the average o f the six trials prior to any treatment. Trial 1 represents the trial on w h i c h the sheep were re-introduced to the race after o n e treatment, etc. 30-
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Fig. 2. Mean push-up time for the four groups of sheep o n each trial (E-I = electro-imm o b i l i z a t i o n ) . Trial 0 represents the average o f the six trials prior to any treatment. Trial 1 represents the trial o n w h i c h the sheep were re-introduced to the race after one treatment, etc.
319 Analysis of variance indicated a highly significant trial X treatment interaction effect for both transit time (F = 4.64; df = 24,248; P < 0.001) and for push-up time (F = 4.59; df = 24,248; P < 0.001). Transit time on re-exposure to the race some 12 weeks later was significantly longer than the initial transit time prior to any treatment for both groups (F = 15.81; df = 1,18; P < 0.001). However, the group that had been electro-immobilized 12 weeks previously had a significantly longer transit time (F --- 5.83; df = 1,18; P = 0.027) and a significantly longer push-up time (F = 6.91; df = 1,18; P = 0.018) than did the group which had been wired up. The sheep with the two previous experiences of electro-immobilization had an average transit time of 159 s and an average push-up time of 5.4 s following the second series of immobilizations. The corresponding figures for sheep with no prior experience were 261 and 9.2 s, respectively. The differences were not significant for either transit time (F = 3.42; df = 1,18; P = 0.081) or for push-up time (F = 0.83; df = 1 , 1 8 ; P = 0.375). Discussion
Compared with allowing the sheep to run freely through the race, both physical restraint and electro-immobilization increased the time required to run through on subsequent occasions, suggesting that both treatments were aversive. The longest running times were recorded from the immobilized sheep, and considerably more time had to be spent pushing these animals up the race. These results suggest that electro-immobilization is a more aversive experience for sheep than simple mechanical restraint. The attachment of the electrodes and the necessary extra handling appeared to make no significant contribution to this aversiveness. Furthermore, sheep remember this experience for some 12 weeks, supporting Hutson's (1985) findings of long-term m e m o r y of handling experiences. However, the differences between electro-immobilization and physical restraint were not apparent after only one exposure. Furthermore, for all treatments, transit time and push-up time increased with repeated exposure over the first three or four trials. This initial increase does not appear to result from the treatments becoming more aversive with repetition. If anything, sheep with prior experience of electro-immobilization showed a somewhat reduced degree of aversion to the place where they experienced further immobilizations. The slight decline in transit time and push-up time over Trials 5--7 support this. More likely, the initial increase in transit time and push-up time reflects increased learning by the sheep. Sheep may require several experiences in order to be able to predict what will occur at the end of the race. The underlying assumption is that the resistance the sheep show to being taken back to the place where they have been previously immobilized reflects the psychological aversiveness of the treatment. However,
320 it is possible that because of the degree of tetany induced, rePeated immobilization produced muscle soreness. There were no apparent signs of lameness and it seems unlikely that this could be responsible for the continued aversion shown after 12 weeks. Nevertheless, this possibility needs to be examined. EXPERIMENT 2 The aims of this experiment were to: (1) determine if the increased time required to run through a race was specific to the place in which immobilizations occurred, and thus reflected its psychological aversiveness rather than muscular soreness or other physiological after-effects; (2) further explore whether prior experience of electro-immobilization reduced its aversiveness; (3) examine the effect of current amplitude and duration of immobilization on its aversiveness. Method F o r t y 3--6-year-old Merino wethers (liveweight 35--60 kg) were used. Twenty-eight had been subjects in previous experiments and had been electro-immobilized between four and eight times during the preceding 6 months, while 12 had no previous experience of electro-immobilization. The procedure outlined in the previous experiment was followed with the sheep being immobilized after running down the race once a day for 4 days. The total transit time and the total push-up time were recorded prior to the first immobilization and after the fourth immobilization. The "experienced" sheep were also timed running through the race in the reverse direction, both before and after the series of immobilizations. The sheep were allocated to four different groups. Group A was immobilized for 1 min at 30 mA, Group B for 1 min at 60 mA, Group C for 3 min at 30 mA, and Group D for 3 min at 60 mA. The current was kept constant for 60 s and the time taken for the animal to begin breathing was recorded. If the sheep had not begun breathing within 60 s, the current was immediately reduced until breathing occurred and then gradually increased w i t h o u t allowing any further cessation of breathing. Results Following four electro-immobilizations, the average transit time in the normal direction increased from 9.4 to 257.6 s (F = 91.86; df = 1,39; P < 0.001). However, average transit time in the reverse direction actually decreased from 2.7 to 2.2 s (F = 14.86; df = 1,27; P < 0.001). Sheep with no prior experience of electro-immobilization had a much
321 TABLE I Average transit time and push-up time after four immobilizations at each level of current and duration. Latency to breathe (averaged over four trials) at each level of current used
Current (mA) 30
Average transit time (s) Average push-up time (s) Average latency to breathe (s)
60
Duration 1 rain
Duration 3 rain
Duration
Duration
1 rain
3 min
220.2
227.5
294.5
288.0
4.6
4.0
8.5
9.8
22
48
longer transit time (x = 413 s) after four immobilizations than did sheep with prior experience (x = 191 s). This difference was highly significant (F = 25.61; d f = 1,39; P < 0.001). Table I shows the average transit time and push-up time after four immobilizations for each combination o f current and duration, and latency to breathe (averaged over f our trials) at each level of current. Duration o f immobilization had no effect on either transit time (F = 0.00; df = 1,39; P = 0.993) or push-up time (F -- 0.04; df = 1,39; P = 0.842}. The difference in transit time between the 60- and 30-mA groups just failed to reach significance (F = 2.8; df = 1,39; P = 0.10). However, push-up time was significantly higher after 60 mA ( F = 7.80; df = 1,39; P = 0.009). The latency to begin breathing did n o t vary significantly over the four immobilizations given to each sheep (F = 2.00; df = 3,117; P = 0.12), was n o t affected by prior experience of electro-immobilization (F = 1.10; df = 1, 39; P = 0.301), but was significantly greater at 60 than at 30 mA (F = 26.82; df -- 1,39; P < 0.001). The latency to begin breathing (averaged over the f o u r trials) was negatively correlated with b o d y weight, but this was n o t significant (r = - 0 . 2 7 ; n = 27; P = 0.089). The mean latency to begin breathing averaged over the four immobilizations was significantly correlated with both transit time (r = 0.34; n = 40; P = 0.015) and push-up time (r = 0.43; n = 40; P = 0.003} on the subsequent run. To determine if the effects of increasing current on push-up time were mediated by the increased difficulty in breathing, a multiple regression approach was adopted, with bot h current amperage and latency to breathe as simultaneous predictor (independent) variables and push-up time as the criterion (dependent) variable. The regression coefficient for latency to breathe of 0.43 was highly significant (P = 0.006), while t hat for current ( - 0 . 1 3 ) was n o t (P = 0.596).
322 Discussion
The increase in the time required to traverse the race following the series of electro-immobilizations only occurred if the sheep were moving toward the place where they had been previously immobilized and therefore does not result from muscle soreness, difficulty in walking or other physiological after-effects. The aversiveness of electro-immobilization was more dependent upon the current used than on the duration. This appears to be quite a different situation from that of actual electric shock, since numerous studies using laboratory rats have shown that the degree of aversiveness is closely dependent upon both the amperage used and the duration of the shock (Azrin and Holz, 1966; Church, 1969). However, the results suggest that the initial period when the sheep are unable to breath is a significant contributor to the aversiveness of the procedure, and since all animals began to breathe during the first minute, this may explain the lack of effect of increasing the duration of immobilization. Prior experience of electro-immobilization resulted in a significant reduction in transit time and push-up time, suggesting that some form of adaptation occurs. However, this was not mediated by an increasing ease in recovery of breathing. It is not possible at present to determine if this adaptation results from an actual decrease in the aversiveness of electroimmobilization per se, or from some other effect, such as reduction in the novelty of the experience. CONCLUSIONS From a welfare point of view, the acceptability of any handling procedure can only be judged in relation to the alternatives available. One argument for the use of electro-immobilization in handling cattle is that this reduces the stress and trauma resulting from physical restraint. Sheep, however, clearly find electro-immobilization more aversive than simple physical restraint in a sheep-handling machine. Furthermore, the finding that electro-immobilization is aversive indicates that the mechanism of its purported analgesia needs to be carefully examined. A large body of literature indicates that the application of a variety of uncontrollable aversive and stressful treatments, such as forced coldwater swimming and repeated electric shocks, can induce a degree of transient analgesia in laboratory rodents (Maier et al., 1983). The possibility that a degree of analgesia is being obtained only at the cost of exposing the animal to an unacceptably high level of stress must be examined. Attempts to reduce the aversiveness of electro-immobilization should be directed at reducing the period when the animal is unable to breathe. Some analysis of the mechanism that leads to the procedure apparently becoming less aversive with repetition might also prove fruitful.
323
The behavioural measures chosen proved able to discriminate between the different treatments applied to sheep, indicating that this experimental procedure may be a useful alternative to traditional physiological measures (e.g. Kilgour and de Langen, 1970; Syme and Elphick, 1982) in testing the relative aversiveness of a wide range of sheep-handling operations. ACKNOWLEDGEMENTS
This research was performed at the request of the Australian Wool Corporation and, on its recommendations, funded by the Wool Research Trust Fund. Experimental procedures were approved by the University of Melbourne Animal Experimentation Ethics Committee. The Feenix Stockstill and instructions for its use were supplied by Merino Wool Harvesting Pty. Ltd. Professor Adrian Egan, Dr. Roll Beilharz and Dr. Geoff Hutson were instrumental in planning the research, and I am very grateful to them for all the help and encouragement I received. I thank Dr. Paul Hudson (A.W.C.) for help and information supplied, Anne Hargreaves for excellent technical assistance, and Daryl Whitfield and Eric Martin for numerous favours. RESEARCH NOTE
The instrument produces electrical pulses (square wave, DC) of 1.1 ms duration at a frequency of 45 Hz. The o u t p u t voltage varies (up to a maximum of 50 V) so as to produce a constant current, which can be adjusted by the operator up to a maximum of 100 mA. Although the physiological basis of its action is not fully understood, the passage of these pulses across the spinal cord results in generalized muscle contraction and postural immobility. On application of the current, respiration generally ceases and the latency to recover breathing depends upon the current used. Excessive current causes total paralysis of the respiratory muscles and deaths have been reported. Unpublished reports suggest that a degree of analgesia is produced, possibly through release of endogenous opiates, and its use as an alternative to chemical anaesthetics has been suggested. However, doubts remain a b o u t the extent of the analgesia produced (Carter et al., 1983). The effects upon central nervous system activity are being investigated. However, the animals do not appear to lose consciousness. The instrument is freely available in Australia and is currently employed b y some veterinarians. However, the Australian Veterinary Association does not condone its use except for purposes of evaluation ( A N . A , 1984).
REFERENCES Australian Veterinary Association, 1984. A.V.A. News No. 1, 24 February 1984, Australian Veterinary Association, New Brunswick, Vic., p. 8.
324 Azrin, N.H. and Holz, W.C., 1966. Punishment. In: W.K. Honig (Editor), Operant Behaviour. Appleton--Century--Crofts, New York. Baxter, J.R., 1982. The development of a small mobile/transportable automated w o o l harvesting system. In: P.R.W. Hudson (Editor), Proc. 2nd Natl. Conf. Wool Harvesting Research and Development. 10--13 August 1981, Australian Wool Corporation, Sydney. Carter, P.D., Johnston, N.E., Corner, L.A. and Jarrett, R.G., 1983. Observations on the effect of electro-immobilization on the de-horning of cattle. Aust. Vet. J., 60: 17--19. Church, R.M., 1969. Response suppression. In: B.A. Campbell and R.M. Church (Editors), Punishment and Aversive Behaviour. Appleton--Century--Crofts. New York. Fox, M.W., 1984. Farm Animals. University Park Press, Baltimore. Hudson, P.R.W. (Editor), 1982. Proceedings of the Second National Conference on Wool Harvesting Research and Development. 10--13 August 1981, Australian Wool Corporation, Sydney. Hutson, G.D., 1982. Rewarding sheep after handling. In: P.R.W. Hudson (Editor), Proc. 2rid Natl. Conf. Wool Harvesting Research and Development. 10--13 August 1981, Australian Wool Corporation, Sydney. Hutson, G.D., 1985. The influence of barley food rewards on sheep movement through a handling system. Appl. Anim. Behav. Sci., 14: 263--274. Kilgour, R. and DeLangen, H., 1970. Stress in sheep resulting from management practices. Proc. N.Z. Soc. Anim. Prod., 30: 65--76. Maier, S.F., Drugan, R., Grau, J.W., Hyson, R., MacLennan, A.J., Moye, T., Madden, J. and Barchas, J.D., 1983. Learned helplessness, pain inhibition and the endogenous opiates. In: M.D. Zeiler and P. Harzem (Editors), Advances in the Analysis of Behaviour. Vol. 3. Wiley, New York. Smith, J.B., 1983. Animal welfare and the Australian veterinarian. Aust. Vet. J., 60: 299--302. Syme, L.A. and Elphick, G.R., 1982. Heart-rate and the behaviour of sheep in yards. Appl. Anim. Ethol., 9: 31--35.
315
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
AVERSION OF SHEEP TO ELECTRO-IMMOBILIZATION PHYSICAL RESTRAINT
AND
J. RUSHEN 1
School of Agriculture and Forestry, University of Melbourne, Parkville, Vic. 3052 (Australia) (Accepted for publication 28 February 1986)
ABSTRACT Rushen, J., 1986. Aversion of sheep to electro-immobilization and physical restraint. Appl. Anim. Behav. Sci., 15: 315--324. Thirty-six Merino wethers were forced along a sheep race and were either electroimmobilized using a commercially-available instrument, restrained with the electroimmobilizer electrodes attached, physically restrained in a sheep-handling machine or allowed to run freely through the race. The degree of aversion shown to the place where the treatment occurred was measured by the time taken by the sheep to run through the race on a subsequent occasion ("transit time") and the push-up time required. All forms of restraint increased the push-up and transit times. Sheep that had been electro-immobilized had a greater average transit time after four treatments and a greater average push-up time after two treatments than sheep that were physically restrained, with or without the electrodes attached. These results suggest that sheep find electro-immobilization more aversive than physical restraint. Push-up time was increased if a high current was used, but was unrelated to the duration of electro-immobilization (up to 3 rain). Increasing the current increased the time required by the sheep to recover breathing, which was strongly and positively related to subsequent push-up time. The degree of aversion shown decreases with experience of electro-immobilization.
INTRODUCTION The effects of routine veterinary and animal husbandry procedures on t h e w e l f a r e o f d o m e s t i c a n i m a l s is i n c r e a s i n g l y e n g a g i n g t h e a t t e n t i o n o f v e t e r i n a r y a n d a n i m a l s c i e n t i s t s in m o s t w e s t e r n c o u n t r i e s (e.g. S m i t h , 1983; Fox, 1984). In Australia, the development of fully automated systems f o r s h e a r i n g s h e e p (e.g. H u d s o n , 1 9 8 2 ) m a y h a v e t h e p o t e n t i a l t o i n c r e a s e the degree of stress to which large numbers of animals are routinely exp o s e d . O f p a r t i c u l a r i n t e r e s t is t h e p r o p o s e d u s e o f p u l s e d , l o w - v o l t a g e electric current to immobilize animals, particularly sheep, by producing 1Present address: Animal Research Centre, Agriculture Canada, Ottawa, Ont. K I A 0C6, Canada. 0168-1591/86/$03.50
© 1986 Elsevier Science Publishers B.V.
316
a degree o f involuntary contraction o f the skeletal muscles (Baxter, 1982). An instrument that does this is commercially available 1, and it has been p r o m o t e d by some veterinarians as a useful tool in reducing the stress associated with the physical restraint of cattle. However, Carter et al. (1983) express their belief t hat cattle may find such electro-immobilization to be an unpleasant experience. However, this was a largely subjective judgement. An investigation of the effect that any procedure used in handling animals has on their welfare should include an assessment of the animal's own experience of that procedure. The challenge is to find an objectively measurable parameter (physiological or behavioural) that has a defendable theoretical link with an animal's experiences, and which can therefore be used to make inferences a bout the animal's subjective state while undergoing the treatment. One view o f the function of subjective experiences is to consider them as being instrumental in modifying future behaviour so that situations that are experienced as unpleasant can be avoided in the future. By this logic, if a sheep finds electro-immobilization aversive or unpleasant, it will tend to avoid the place where it has been previously immobilized. This can be quantified by measuring any increase in the time required to move the animal through a race. This measure has been shown to be sensitive to a variety of aversive and rewarding treatments (Hutson, 1982, 1985). EXPERIMENT 1 This ex p er imen t examined the following points: (1) if sheep f o u n d electro-immobilization aversive: (2) wh eth er it was more or less aversive than physical restraint; (3) if sheep r e m e m b e r e d the experience over a period of several months; (4) wh eth er prior experience of electro-immobilization increased or decreased its aversiveness.
Method Thirty-six 3--6-year-old unshorn Merino wethers (35--60 kg liveweight), with no observable physical disabilities, were selected. All had experience o f f r eq u en t h u m a n cont act and handling, but none had previously been electro-immobilized. The sheep were allotted to four t r e a t m e n t groups. This was achieved by running the flock through a race, taking the first four sheep to run t hr ough and allotting one to each group. This was repeated for the n ex t group of four, and so on. The sheep were then marked according to the t r e a t m e n t group to which t hey had been allocated, and the flock was re-assembled. i Feenix Stockstill ®, Feenix International Pty. Ltd., Tarlee, S.A. 5411, Australia.
317 Individual sheep were taken f r om the group n o t in any fixed order but simply according to how easy t h e y were to catch. Each was placed at the head o f a 7-m-long race at the end of which was a " M o f f a t - - V i r t u e " sheephandling machine. This machine consists of two "jaws" that are hinged at the b o t t o m . As the sheep runs between the jaws these can be pulled t o g eth er so as to catch the sheep and hold it in an upright position. The race was divided into four sections and the sheep was allowed a m a x i m u m time o f 2 min to run through each section. The experi m ent er stood at the head o f the race and, once this time had elapsed, moved towards the animal, pushing it if necessary, until it entered the n e x t section. As far as possible, a standard force was applied to the animal. The total time required to run through the race ("transit t i m e " ) and the total time spent moving toward and pushing the sheep ("push-up t i m e " ) were recorded. On the first day, sheep were allowed to run freely through the race six times to allow th e m to become accustomed to it. On the second day, the sheep were subjected to one of f our treatments depending on which group t h e y had previously been allotted to. Ca) Free-running (n = 6). Sheep were allowed to run freely through the race and into a catching pen. (b) Physical restraint (n = 10). After running through the race, the animals were immediately caught and restrained in an upright position in the sheep handling machine for 2.5 min. (c) Full electro-immobilization in = 10). After running through the race and being caught in the sheep-handling machine, the animals were electro-immobilized using a commercially available hand-held Feenix Stockstill electro-immobilizer (see Research Note at the end of this paper). A p p r o x i m a t e l y 30 s after catching the sheep, a needle electrode was inserted under the skin at the base of the tail, and an alligator-clip electrode was placed on the inside o f the contralateral cheek. A maxim u m current of 40--60 mA was initially applied. This was immediately reduced until the animal started breathing and was then gradually increased. The final level was chosen so as to allow regular breathing and in all cases was between 30 and 50 mA. No animal was k e p t witho u t breathing for longer than 15 s. (d) Wired-up (n = 10). The animals were restrained in the handler for 2.5 min with the immobilizer electrodes attached in the manner described above. The current was not t ur ne d on. The procedure was repeated 4 h later, and then twice a day for the next 3 days. On the final day, the animals were timed running through the race a third time, but no t r e a t m e n t was applied. Twelve weeks after the conclusion o f this study, the sheep from the wired-up group and from the electro-immobilized group were run through the race again and timed. In order to de t e r m i ne if prior experience of electro-immobilization alters aversiveness, a second group of 20 newly shorn merino wethers with no previous experience o f electro-immobilization were selected. Ten of
318
the animals were immobilized in the manner described above once a day for 2 consecutive days in a small cage quite separate from the race system. The 10 remaining sheep were restrained in the same cage for 2 min with the electrodes attached, but the current was n o t turned on. This was also done once a day for 2 days. Seventy-two hours later, all animals were run through the race described in the previous experiment and electro-immobilized in the standard manner. This was repeated twice more over 2 days. Transit time and push-up time following the third immobilization were recorded. Results Figure 1 shows the average transit time and Fig. 2 shows the average push-up time for the four groups of sheep for the six trials prior to treatment and for the eight trials after each treatment. 400 []
300
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Fig. 1. Mean transit time for the four groups o f sheep on each trial (E-I = electro-imm o b i l i z a t i o n ) . Trial 0 represents the average o f the six trials prior to any treatment. Trial 1 represents the trial on w h i c h the sheep were re-introduced to the race after o n e treatment, etc. 30-
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Trial
Fig. 2. Mean push-up time for the four groups of sheep o n each trial (E-I = electro-imm o b i l i z a t i o n ) . Trial 0 represents the average o f the six trials prior to any treatment. Trial 1 represents the trial o n w h i c h the sheep were re-introduced to the race after one treatment, etc.
319 Analysis of variance indicated a highly significant trial X treatment interaction effect for both transit time (F = 4.64; df = 24,248; P < 0.001) and for push-up time (F = 4.59; df = 24,248; P < 0.001). Transit time on re-exposure to the race some 12 weeks later was significantly longer than the initial transit time prior to any treatment for both groups (F = 15.81; df = 1,18; P < 0.001). However, the group that had been electro-immobilized 12 weeks previously had a significantly longer transit time (F --- 5.83; df = 1,18; P = 0.027) and a significantly longer push-up time (F = 6.91; df = 1,18; P = 0.018) than did the group which had been wired up. The sheep with the two previous experiences of electro-immobilization had an average transit time of 159 s and an average push-up time of 5.4 s following the second series of immobilizations. The corresponding figures for sheep with no prior experience were 261 and 9.2 s, respectively. The differences were not significant for either transit time (F = 3.42; df = 1,18; P = 0.081) or for push-up time (F = 0.83; df = 1 , 1 8 ; P = 0.375). Discussion
Compared with allowing the sheep to run freely through the race, both physical restraint and electro-immobilization increased the time required to run through on subsequent occasions, suggesting that both treatments were aversive. The longest running times were recorded from the immobilized sheep, and considerably more time had to be spent pushing these animals up the race. These results suggest that electro-immobilization is a more aversive experience for sheep than simple mechanical restraint. The attachment of the electrodes and the necessary extra handling appeared to make no significant contribution to this aversiveness. Furthermore, sheep remember this experience for some 12 weeks, supporting Hutson's (1985) findings of long-term m e m o r y of handling experiences. However, the differences between electro-immobilization and physical restraint were not apparent after only one exposure. Furthermore, for all treatments, transit time and push-up time increased with repeated exposure over the first three or four trials. This initial increase does not appear to result from the treatments becoming more aversive with repetition. If anything, sheep with prior experience of electro-immobilization showed a somewhat reduced degree of aversion to the place where they experienced further immobilizations. The slight decline in transit time and push-up time over Trials 5--7 support this. More likely, the initial increase in transit time and push-up time reflects increased learning by the sheep. Sheep may require several experiences in order to be able to predict what will occur at the end of the race. The underlying assumption is that the resistance the sheep show to being taken back to the place where they have been previously immobilized reflects the psychological aversiveness of the treatment. However,
320 it is possible that because of the degree of tetany induced, rePeated immobilization produced muscle soreness. There were no apparent signs of lameness and it seems unlikely that this could be responsible for the continued aversion shown after 12 weeks. Nevertheless, this possibility needs to be examined. EXPERIMENT 2 The aims of this experiment were to: (1) determine if the increased time required to run through a race was specific to the place in which immobilizations occurred, and thus reflected its psychological aversiveness rather than muscular soreness or other physiological after-effects; (2) further explore whether prior experience of electro-immobilization reduced its aversiveness; (3) examine the effect of current amplitude and duration of immobilization on its aversiveness. Method F o r t y 3--6-year-old Merino wethers (liveweight 35--60 kg) were used. Twenty-eight had been subjects in previous experiments and had been electro-immobilized between four and eight times during the preceding 6 months, while 12 had no previous experience of electro-immobilization. The procedure outlined in the previous experiment was followed with the sheep being immobilized after running down the race once a day for 4 days. The total transit time and the total push-up time were recorded prior to the first immobilization and after the fourth immobilization. The "experienced" sheep were also timed running through the race in the reverse direction, both before and after the series of immobilizations. The sheep were allocated to four different groups. Group A was immobilized for 1 min at 30 mA, Group B for 1 min at 60 mA, Group C for 3 min at 30 mA, and Group D for 3 min at 60 mA. The current was kept constant for 60 s and the time taken for the animal to begin breathing was recorded. If the sheep had not begun breathing within 60 s, the current was immediately reduced until breathing occurred and then gradually increased w i t h o u t allowing any further cessation of breathing. Results Following four electro-immobilizations, the average transit time in the normal direction increased from 9.4 to 257.6 s (F = 91.86; df = 1,39; P < 0.001). However, average transit time in the reverse direction actually decreased from 2.7 to 2.2 s (F = 14.86; df = 1,27; P < 0.001). Sheep with no prior experience of electro-immobilization had a much
321 TABLE I Average transit time and push-up time after four immobilizations at each level of current and duration. Latency to breathe (averaged over four trials) at each level of current used
Current (mA) 30
Average transit time (s) Average push-up time (s) Average latency to breathe (s)
60
Duration 1 rain
Duration 3 rain
Duration
Duration
1 rain
3 min
220.2
227.5
294.5
288.0
4.6
4.0
8.5
9.8
22
48
longer transit time (x = 413 s) after four immobilizations than did sheep with prior experience (x = 191 s). This difference was highly significant (F = 25.61; d f = 1,39; P < 0.001). Table I shows the average transit time and push-up time after four immobilizations for each combination o f current and duration, and latency to breathe (averaged over f our trials) at each level of current. Duration o f immobilization had no effect on either transit time (F = 0.00; df = 1,39; P = 0.993) or push-up time (F -- 0.04; df = 1,39; P = 0.842}. The difference in transit time between the 60- and 30-mA groups just failed to reach significance (F = 2.8; df = 1,39; P = 0.10). However, push-up time was significantly higher after 60 mA ( F = 7.80; df = 1,39; P = 0.009). The latency to begin breathing did n o t vary significantly over the four immobilizations given to each sheep (F = 2.00; df = 3,117; P = 0.12), was n o t affected by prior experience of electro-immobilization (F = 1.10; df = 1, 39; P = 0.301), but was significantly greater at 60 than at 30 mA (F = 26.82; df -- 1,39; P < 0.001). The latency to begin breathing (averaged over the f o u r trials) was negatively correlated with b o d y weight, but this was n o t significant (r = - 0 . 2 7 ; n = 27; P = 0.089). The mean latency to begin breathing averaged over the four immobilizations was significantly correlated with both transit time (r = 0.34; n = 40; P = 0.015) and push-up time (r = 0.43; n = 40; P = 0.003} on the subsequent run. To determine if the effects of increasing current on push-up time were mediated by the increased difficulty in breathing, a multiple regression approach was adopted, with bot h current amperage and latency to breathe as simultaneous predictor (independent) variables and push-up time as the criterion (dependent) variable. The regression coefficient for latency to breathe of 0.43 was highly significant (P = 0.006), while t hat for current ( - 0 . 1 3 ) was n o t (P = 0.596).
322 Discussion
The increase in the time required to traverse the race following the series of electro-immobilizations only occurred if the sheep were moving toward the place where they had been previously immobilized and therefore does not result from muscle soreness, difficulty in walking or other physiological after-effects. The aversiveness of electro-immobilization was more dependent upon the current used than on the duration. This appears to be quite a different situation from that of actual electric shock, since numerous studies using laboratory rats have shown that the degree of aversiveness is closely dependent upon both the amperage used and the duration of the shock (Azrin and Holz, 1966; Church, 1969). However, the results suggest that the initial period when the sheep are unable to breath is a significant contributor to the aversiveness of the procedure, and since all animals began to breathe during the first minute, this may explain the lack of effect of increasing the duration of immobilization. Prior experience of electro-immobilization resulted in a significant reduction in transit time and push-up time, suggesting that some form of adaptation occurs. However, this was not mediated by an increasing ease in recovery of breathing. It is not possible at present to determine if this adaptation results from an actual decrease in the aversiveness of electroimmobilization per se, or from some other effect, such as reduction in the novelty of the experience. CONCLUSIONS From a welfare point of view, the acceptability of any handling procedure can only be judged in relation to the alternatives available. One argument for the use of electro-immobilization in handling cattle is that this reduces the stress and trauma resulting from physical restraint. Sheep, however, clearly find electro-immobilization more aversive than simple physical restraint in a sheep-handling machine. Furthermore, the finding that electro-immobilization is aversive indicates that the mechanism of its purported analgesia needs to be carefully examined. A large body of literature indicates that the application of a variety of uncontrollable aversive and stressful treatments, such as forced coldwater swimming and repeated electric shocks, can induce a degree of transient analgesia in laboratory rodents (Maier et al., 1983). The possibility that a degree of analgesia is being obtained only at the cost of exposing the animal to an unacceptably high level of stress must be examined. Attempts to reduce the aversiveness of electro-immobilization should be directed at reducing the period when the animal is unable to breathe. Some analysis of the mechanism that leads to the procedure apparently becoming less aversive with repetition might also prove fruitful.
323
The behavioural measures chosen proved able to discriminate between the different treatments applied to sheep, indicating that this experimental procedure may be a useful alternative to traditional physiological measures (e.g. Kilgour and de Langen, 1970; Syme and Elphick, 1982) in testing the relative aversiveness of a wide range of sheep-handling operations. ACKNOWLEDGEMENTS
This research was performed at the request of the Australian Wool Corporation and, on its recommendations, funded by the Wool Research Trust Fund. Experimental procedures were approved by the University of Melbourne Animal Experimentation Ethics Committee. The Feenix Stockstill and instructions for its use were supplied by Merino Wool Harvesting Pty. Ltd. Professor Adrian Egan, Dr. Roll Beilharz and Dr. Geoff Hutson were instrumental in planning the research, and I am very grateful to them for all the help and encouragement I received. I thank Dr. Paul Hudson (A.W.C.) for help and information supplied, Anne Hargreaves for excellent technical assistance, and Daryl Whitfield and Eric Martin for numerous favours. RESEARCH NOTE
The instrument produces electrical pulses (square wave, DC) of 1.1 ms duration at a frequency of 45 Hz. The o u t p u t voltage varies (up to a maximum of 50 V) so as to produce a constant current, which can be adjusted by the operator up to a maximum of 100 mA. Although the physiological basis of its action is not fully understood, the passage of these pulses across the spinal cord results in generalized muscle contraction and postural immobility. On application of the current, respiration generally ceases and the latency to recover breathing depends upon the current used. Excessive current causes total paralysis of the respiratory muscles and deaths have been reported. Unpublished reports suggest that a degree of analgesia is produced, possibly through release of endogenous opiates, and its use as an alternative to chemical anaesthetics has been suggested. However, doubts remain a b o u t the extent of the analgesia produced (Carter et al., 1983). The effects upon central nervous system activity are being investigated. However, the animals do not appear to lose consciousness. The instrument is freely available in Australia and is currently employed b y some veterinarians. However, the Australian Veterinary Association does not condone its use except for purposes of evaluation ( A N . A , 1984).
REFERENCES Australian Veterinary Association, 1984. A.V.A. News No. 1, 24 February 1984, Australian Veterinary Association, New Brunswick, Vic., p. 8.
324 Azrin, N.H. and Holz, W.C., 1966. Punishment. In: W.K. Honig (Editor), Operant Behaviour. Appleton--Century--Crofts, New York. Baxter, J.R., 1982. The development of a small mobile/transportable automated w o o l harvesting system. In: P.R.W. Hudson (Editor), Proc. 2nd Natl. Conf. Wool Harvesting Research and Development. 10--13 August 1981, Australian Wool Corporation, Sydney. Carter, P.D., Johnston, N.E., Corner, L.A. and Jarrett, R.G., 1983. Observations on the effect of electro-immobilization on the de-horning of cattle. Aust. Vet. J., 60: 17--19. Church, R.M., 1969. Response suppression. In: B.A. Campbell and R.M. Church (Editors), Punishment and Aversive Behaviour. Appleton--Century--Crofts. New York. Fox, M.W., 1984. Farm Animals. University Park Press, Baltimore. Hudson, P.R.W. (Editor), 1982. Proceedings of the Second National Conference on Wool Harvesting Research and Development. 10--13 August 1981, Australian Wool Corporation, Sydney. Hutson, G.D., 1982. Rewarding sheep after handling. In: P.R.W. Hudson (Editor), Proc. 2rid Natl. Conf. Wool Harvesting Research and Development. 10--13 August 1981, Australian Wool Corporation, Sydney. Hutson, G.D., 1985. The influence of barley food rewards on sheep movement through a handling system. Appl. Anim. Behav. Sci., 14: 263--274. Kilgour, R. and DeLangen, H., 1970. Stress in sheep resulting from management practices. Proc. N.Z. Soc. Anim. Prod., 30: 65--76. Maier, S.F., Drugan, R., Grau, J.W., Hyson, R., MacLennan, A.J., Moye, T., Madden, J. and Barchas, J.D., 1983. Learned helplessness, pain inhibition and the endogenous opiates. In: M.D. Zeiler and P. Harzem (Editors), Advances in the Analysis of Behaviour. Vol. 3. Wiley, New York. Smith, J.B., 1983. Animal welfare and the Australian veterinarian. Aust. Vet. J., 60: 299--302. Syme, L.A. and Elphick, G.R., 1982. Heart-rate and the behaviour of sheep in yards. Appl. Anim. Ethol., 9: 31--35.