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Neuromata in docked lambs' tails
Research in VeterinaryScience1992, 52, 389-390
Neuromata in docked lambs' tails N. P. FRENCH, K. L. MORGAN, Department of Veterinary Medicine, University of Bristol, Langford House, Langford, Bristol, Avon
Docked and undocked Iambs tails obtained after slaughter were examined grossly and histopathologically. Stump and complex neuromata were identified in docked tails.
TAIL amputation or docking is a routine procedure on sheep farms. It is widely believed that tail docking reduces the risk of myiasis or blowfly strike by decreasing the amount of faecal soiling around the perineum. It has been suggested that tail docking improves the appearance of lambs and the breeding efficiency of ewes (Wohlt et al 1982). Tail docking is usually carried out within 48 hours of birth and a number of methods are used. These include applying rubber rings, cutting with a knife or clippers, or cauterising with a hot iron. In a recent survey over 90 per cent of sheep farmers docked tails by the application of a tight rubber ring (N. P. French, unpublished data). Ischaemia and necrosis follows, resulting in loss of the tail distal to the ring. Both pairs of coccygeal nerves are severed. The acute level of distress following the application of a rubber ring to the tail has been demonstrated by measuring behavioural responses and changes in plasma immunoreactive B endorphin and cortisol (Shutt et al 1988, Mellor and Murray 1989). No studies of the chronic effects of tail amputation in lambs were found. Neuroma formation is believed to be the inevitable result of peripheral nerve transection with avulsion of the distal segment (Wall and Melzack 1984). Previous studies on the effects of peripheral nerve amputation, have shown that neuroma formation is often associated with abnormal nerve discharges (Scadding 1981, Blumberg and Janig 1984, Breward and Gentle 1985). This excitability is an important feature of neuromata and is implicated in post amputation pain. Chronic pain and self mutilation have been reported following amputation of peripheral nerves, including tail docking in dogs (Gross and Carr 1990). Neuromata have been demonstrated following such mutilations as beak and toe amputation in chickens (Gentle 1986, Gentle and Hunter 1988), tail docking in pigs (Simonsen et al 1991) and tail docking in dogs (Gross and Carr 1990). The occurrence of neuromata
FIG 1: Photomicrograph of a nerve stump neuroma stained with haematoxylin and eosin, showing the irregular swirling pattern of nerve fibres. Bar represents 100 ~tm
FIG 2: Discrete irregular nerve bundles within the scar tissue of the tail stump. Bar represents 100 ~tm
following tail docking in sheep is reported in this communication. Tails from 12 docked and six undocked lambs were obtained after slaughter, when lambs were between four and six months old. Six docked and two undocked tails were dissected to display the gross coccygeal innervation. In docked tails, the distal ends of the dorsal and ventral coccygeal nerves were firmly adherent to 389
390
N. P. French, K. L. Morgan
scar tissue and difficult to dissect free from surrounding tissue. Obvious swellings were visible on three distal nerve stumps from three different docked tails. N o swellings were visible on nerves from undocked lambs. The remaining 10 tails were divided in half dorsoventrally. Longitudinal sections, approximately 3 mm thick, were taken from each half. These were decalcified in 10 per cent formic acid and fixed in formalin. Serial sections were stained with either haematoxylin and eosin, haematoxylin van Geisen or solochrome cyanine. Histologically, neuromata were identified as swellings at the distal ends of the main coccygeal nerve trunks on two docked tails. These contained swirling, tortuous knots of axons surrounded by fibroblasts (Fig 1). In sections from two other docked tails multiple, discrete, irregularly distributed nerve bundles were seen within the connective and scar tissue of the tail stump (Fig 2). These were similar to the complex neuromata seen following beak amputation in chickens (Gentle 1986). The presence of terminal neuromata and irregular innervation in docked lambs' tails suggests that chronic pain or increased sensitivity may be present long after amputation. Further behavioural and neurophysiological studies are needed to investigate the routine practice of tail amputation.
References BLUMBERG, H. & JANIG, W. (1984) Discharge pattern of afferent fibres from a neuroma. Pain 20, 335-353 BREWARD, J. & GENTLE, M. J. (1985) Neuroma formation and abnormal afferent nerve discharges after partial beak amputation (beak trimming) in poultry. Experientia 41, 1132-1134 GENTLE, M. J. (1986) Neuroma formation following partial beak amputation (beak trimming) in the chicken. Research in Veterinary Science 41, 383-385 GENTLE, M. J. & HUNTER, L. H. (1988) Neural consequences of partial toe amputation in chickens. Research in Veterinary Science 45, 374-376 GROSS, T. L. & CARR, S. H. (1990) Amputation neuroma of docked tails in dogs. Veterinary Pathology 27, 61-62 MELLOR, D. J. & MURRAY, L, (1989) Effects of tail docking and castration on behaviour and plasma cortisol concentrations in young lambs. Research in Veterinary Science 46, 387-391 SCADDING, J. W. (1981) Development of ongoing activity, mechanosensitivity, and adrenaline sensitivity in severed peripheral nerve axons. Experimental Neurology 73, 345-364 SHUTT, D. A., FELL, L. R., CONNELL, R. & BELL, A. K. (1988) Stress responses in lambs docked and castrated surgically or by the application of rubber rings. Australian Veterinary Journal 65, 5-7 SIMONSEN, H. B., KLINKEN, L. & BLINDSEIL, E. (1991) Histopathology of intact and docked pig tails. British Veterinary Journal 147, 407-412 WALL, P. D. & MELZACK, R. (1984) Textbook of Pain. Edinburgh, Churchill Livingston. p51 WOHLT, J. E., WRIGHT, T. D., SIRIOS, V. S., KNIFFEN, D. M. & LELKES, L. (1982) Effect of docking on health, blood cells and metabolites and growth of Dorset lambs. Journal of Animal Science 54, 23-28
Acknowledgements We would like to thank the staff in the histology laboratory, Comparative Pathology Laboratory, Langford.
Received December 4, 1991 Accepted February 3, 1992
Neuromata in docked lambs' tails N. P. FRENCH, K. L. MORGAN, Department of Veterinary Medicine, University of Bristol, Langford House, Langford, Bristol, Avon
Docked and undocked Iambs tails obtained after slaughter were examined grossly and histopathologically. Stump and complex neuromata were identified in docked tails.
TAIL amputation or docking is a routine procedure on sheep farms. It is widely believed that tail docking reduces the risk of myiasis or blowfly strike by decreasing the amount of faecal soiling around the perineum. It has been suggested that tail docking improves the appearance of lambs and the breeding efficiency of ewes (Wohlt et al 1982). Tail docking is usually carried out within 48 hours of birth and a number of methods are used. These include applying rubber rings, cutting with a knife or clippers, or cauterising with a hot iron. In a recent survey over 90 per cent of sheep farmers docked tails by the application of a tight rubber ring (N. P. French, unpublished data). Ischaemia and necrosis follows, resulting in loss of the tail distal to the ring. Both pairs of coccygeal nerves are severed. The acute level of distress following the application of a rubber ring to the tail has been demonstrated by measuring behavioural responses and changes in plasma immunoreactive B endorphin and cortisol (Shutt et al 1988, Mellor and Murray 1989). No studies of the chronic effects of tail amputation in lambs were found. Neuroma formation is believed to be the inevitable result of peripheral nerve transection with avulsion of the distal segment (Wall and Melzack 1984). Previous studies on the effects of peripheral nerve amputation, have shown that neuroma formation is often associated with abnormal nerve discharges (Scadding 1981, Blumberg and Janig 1984, Breward and Gentle 1985). This excitability is an important feature of neuromata and is implicated in post amputation pain. Chronic pain and self mutilation have been reported following amputation of peripheral nerves, including tail docking in dogs (Gross and Carr 1990). Neuromata have been demonstrated following such mutilations as beak and toe amputation in chickens (Gentle 1986, Gentle and Hunter 1988), tail docking in pigs (Simonsen et al 1991) and tail docking in dogs (Gross and Carr 1990). The occurrence of neuromata
FIG 1: Photomicrograph of a nerve stump neuroma stained with haematoxylin and eosin, showing the irregular swirling pattern of nerve fibres. Bar represents 100 ~tm
FIG 2: Discrete irregular nerve bundles within the scar tissue of the tail stump. Bar represents 100 ~tm
following tail docking in sheep is reported in this communication. Tails from 12 docked and six undocked lambs were obtained after slaughter, when lambs were between four and six months old. Six docked and two undocked tails were dissected to display the gross coccygeal innervation. In docked tails, the distal ends of the dorsal and ventral coccygeal nerves were firmly adherent to 389
390
N. P. French, K. L. Morgan
scar tissue and difficult to dissect free from surrounding tissue. Obvious swellings were visible on three distal nerve stumps from three different docked tails. N o swellings were visible on nerves from undocked lambs. The remaining 10 tails were divided in half dorsoventrally. Longitudinal sections, approximately 3 mm thick, were taken from each half. These were decalcified in 10 per cent formic acid and fixed in formalin. Serial sections were stained with either haematoxylin and eosin, haematoxylin van Geisen or solochrome cyanine. Histologically, neuromata were identified as swellings at the distal ends of the main coccygeal nerve trunks on two docked tails. These contained swirling, tortuous knots of axons surrounded by fibroblasts (Fig 1). In sections from two other docked tails multiple, discrete, irregularly distributed nerve bundles were seen within the connective and scar tissue of the tail stump (Fig 2). These were similar to the complex neuromata seen following beak amputation in chickens (Gentle 1986). The presence of terminal neuromata and irregular innervation in docked lambs' tails suggests that chronic pain or increased sensitivity may be present long after amputation. Further behavioural and neurophysiological studies are needed to investigate the routine practice of tail amputation.
References BLUMBERG, H. & JANIG, W. (1984) Discharge pattern of afferent fibres from a neuroma. Pain 20, 335-353 BREWARD, J. & GENTLE, M. J. (1985) Neuroma formation and abnormal afferent nerve discharges after partial beak amputation (beak trimming) in poultry. Experientia 41, 1132-1134 GENTLE, M. J. (1986) Neuroma formation following partial beak amputation (beak trimming) in the chicken. Research in Veterinary Science 41, 383-385 GENTLE, M. J. & HUNTER, L. H. (1988) Neural consequences of partial toe amputation in chickens. Research in Veterinary Science 45, 374-376 GROSS, T. L. & CARR, S. H. (1990) Amputation neuroma of docked tails in dogs. Veterinary Pathology 27, 61-62 MELLOR, D. J. & MURRAY, L, (1989) Effects of tail docking and castration on behaviour and plasma cortisol concentrations in young lambs. Research in Veterinary Science 46, 387-391 SCADDING, J. W. (1981) Development of ongoing activity, mechanosensitivity, and adrenaline sensitivity in severed peripheral nerve axons. Experimental Neurology 73, 345-364 SHUTT, D. A., FELL, L. R., CONNELL, R. & BELL, A. K. (1988) Stress responses in lambs docked and castrated surgically or by the application of rubber rings. Australian Veterinary Journal 65, 5-7 SIMONSEN, H. B., KLINKEN, L. & BLINDSEIL, E. (1991) Histopathology of intact and docked pig tails. British Veterinary Journal 147, 407-412 WALL, P. D. & MELZACK, R. (1984) Textbook of Pain. Edinburgh, Churchill Livingston. p51 WOHLT, J. E., WRIGHT, T. D., SIRIOS, V. S., KNIFFEN, D. M. & LELKES, L. (1982) Effect of docking on health, blood cells and metabolites and growth of Dorset lambs. Journal of Animal Science 54, 23-28
Acknowledgements We would like to thank the staff in the histology laboratory, Comparative Pathology Laboratory, Langford.
Received December 4, 1991 Accepted February 3, 1992