J. Rushen, P. Congdon
School of Agriculture and Forestry,University of Melbourne
Parkville, Victoria 3052
Australian Veterinary Journal, Volume 63 No.11 (November 1986) page 373
(Accepted for publication 23 April 1986)
Use of pulsed low voltage electric current to restrain sheep for automated shearing is being considered (Baxter 1982). However, sheep resist being taken back to the place where they were previously electro-immobilised, which shows they are averse to it ( Rusher 1986). Electro-immobilisation also elevates plasma levels of cortisol, the rise being higher than for physical restraint (Jephcott el al 1985).
How significant is this aversion? Is it in the normal range for treatments that are routinely applied to sheep? Or is it substantially higher than that currently accepted? There is no data on the relative aversions of sheep to handling operations. However, studies of cortisol levels and packed cell volume (Kilgour and De Langen 1970; A Hargreaves, personal communication) suggest that, compared with drafting, crutching, drenching, dipping and transport, shearing is among the more physiologically stressful of the routine treatments that sheep undergo. This, of course, excludes one-off surgical operations, such as mulesing and castration.
In order to compare the relative degree of aversion to electro-immobilisation and to shearing, we allowed the sheep to "choose" between the 2 treatments, and examined their preferences. Sheep can make consistent choices between such handling treatments (Rusher, in press).
Twelve 3 to 5-year-old Merino wethers weighing 35 to 60 kg were taken individually from a group and forced to run down a Y-shaped race. After entering one of the 2 arms of the race, sheep then ran into a wire cage. Depending upon which arm it chose to enter, the sheep was then either electro-immobilised or removed and partially shorn. Half of the sheep were shorn if they entered the left arm, and half were shorn if they entered the right, thus controlling any preference for turning left or right. A hand-held electro-immobiliser was used with one needle electrode inserted approximately 2 cm under the skin at the base of the tail, and the second, an alligator clip electrode, making contact with the inside of the contralateral cheek. A current of 30 to 35 mA was applied for 45 to 60 sec. The sheep remained standing, being supported by the sides of the cage. Shearing was carried out in the normal manner for 45 to 60 sec, at a rate that would have required 10 min to remove all of the wool. Thus, the sheep were only partly shorn on each trial, and the whole procedure could be repeated a number of times.
Initially, 2 "forced choices" were given during which the individual sheep was forced down one arm of the race and either shorn or electro-immobilised, and then forced down the other arm. Following this, the sheep was allowed 12 consecutive "free choices ", being shorn or electro-immobilised after every choice, depending upon which arm of the race they chose to enter.
|Sheep||Number of trials on which sheep chose|
Figure 1 shows the percentage of sheep that chose electro-immobilisation on each of the 12 free choice trials. Overall, there was a slight bias towards their choosing shearing. Chi square tests showed that this bias was significant only on trial I and trial 9 (.05 > p > .01). Table I shows for each sheep the number of trials on which it chose to be shorn or to be electro-immobilised. No sheep chose electro-immobilisation more frequently than it did shearing, although 3 of the sheep seemed indifferent. Nine sheep showed a preference for shorn. The mean proportion of choices for shearing was .625 (SD = .110). This was unlikely to occur if there was no overall preference for shearing (t=3.96 df=11 p < .01).
No strong preference was exhibited, although there was a bias by the sheep towards the choice of being shorn. It seems that sheep find electro-immobilisation to be at least as stressful as being shorn for an equivalent length of time, suggesting that the degree of aversion is not trivial. There was little evidence that electro-immobilisation was markedly more stressful, suggesting that the degree of aversion felt may be of the same order of magnitude as that for other routine sheep handling operations. However, bearing in mind the low level of current used, it may be wise to treat this suggestion with some caution, at least until a treatment is found that is unequivocally more stressful than electro-immobilisation.
This project was contracted to the University of Melbourne by the Australian Wool Corporation. It was funded by the Wool Research Trust Fund upon recommendations of the Australian Wool Corporation as a grant to Dr. R.G. Beilharz, Professor A.R. Egan and Dr. G.D. Hutson. The modified Feenix Stockstill was supplied by Merino Wool Harvesting Pty Ltd. Use of the electro-immobiliser for experimental purposes was approved by the University of Melbourne Animal Experimentation Ethics Committee. We thank Dr. P.R.W. Hudson (Australian Wool Corporation) for help and information.
Baxter, J R (1982) ‹In: Proc 2nd National Conference on Wool Harvesting Research and Development Aust Wool Corp, Sydney
Jephcott, H, McMillen, I C, Rushen, I, Hargreaves A and Thorburn G (1985) ‹Proc Aust Physiol Pharmacol Sc 16:15
Kilgour, R and De Langen, H (1970) Proceedings of New Zealand Animal Producers 30:65
Rushen, I (1986) Australian Veterinary Journal 63:63
Rushen, I (1987) Applied Animal Behaviour Science (In press)
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