Characterization of short- and long-term mechanical sensitisation following surgical tail amputation in pigs. By Pierpaolo Di Giminiani, Sandra A. Edwards, Emma M. Malcolm, Matthew C. Leach, Mette S. Herskin & Dale A. Sandercock. 2017. Nature Scientific Reports.
Commercial pigs are frequently exposed to tail mutilations in the form of preventive husbandry procedures (tail docking) or as a result of abnormal behaviour (tail biting). Although tissue and nerve injuries are well-described causes of pain hypersensitivity in humans and in rodent animal models, there is no information on the changes in local pain sensitivity induced by tail injuries in pigs. To determine the temporal profile of sensitisation, pigs were exposed to surgical tail resections and mechanical nociceptive thresholds (MNT) were measured in the acute (one week post-operatively) and in the long-term (either eight or sixteen weeks post-surgery) phase of recovery. The influence of the degree of amputation on MNTs was also evaluated by comparing three different tail-resection treatments (intact, ‘short tail’, ‘long tail’). A significant reduction in MNTs one week following surgery suggests the occurrence of acute sensitisation. Long-term hypersensitivity was also observed in tail-resected pigs at either two or four months following surgery. Tail amputation in pigs appears to evoke acute and sustained changes in peripheral mechanical sensitivity, which resemble features of neuropathic pain reported in humans and other species and provides new information on implications for the welfare of animals subjected to this type of injury.
See also our article in PigProgreess.
Original title: Approche histologique et neurophysiologie de la douleur liée à la coupe de queue chez les porcelets
Presentation of Dr. Dale Sandercock (SRUC) at a seminar on histological and neurophysiological approaches to pain assessment in young pigs. INRA-PEGASE, St-Gilles, France, December 14th 2015
Concerns exist over the long term consequences of tail docking on possible tail stump pain sensitivity due to the development of traumatic neuromas in injured peripheral nerves. Traumatic neuroma formation may cause detrimental sensory changes in the tail due to altered peripheral and spinal neuronal excitability leading to abnormal sensation or pain. We have investigated tail injury and traumatic neuroma development by histopathological assessment after tail docking and measured the expression of key neuropeptides associated with peripheral nerve regeneration, inflammation and chronic pain. In complimentary studies on tail docking and tail biting, we have developed behavioural assessment approaches to measure mechanical nociceptive thresholds (MNT) in the pig tail in purpose built test set-up using a Pressure Application Measurement (PAM) device. Using these approaches we have determined baseline MNT in intact tails along different regions of the tail and also measured changes in MNT over time in pig with resected tails (simulation of the effect of tail biting). An overview of other Scotland’s Rural College (SRUC) pig health and welfare research projects is also presented.
A recent paper by Valros et al. (2015) shows evidence for changes in monoamine metabolism in the brains of pigs affected by tail biting, both in the victims and the biting pigs.
Tail biting in pigs is a major welfare problem within the swine industry. Even though there is plenty of information on housing and management-related risk factors, the biological bases of this behavioral problem are poorly understood. The aim of this study was to investigate a possible link between tail biting, based on behavioral recordings of pigs during an ongoing outbreak, and certain neurotransmitters in different brain regions of these pigs. We used a total of 33 pigs at a farm with a long-standing problem of tail biting. Three equally big behavioral phenotypic groups, balanced for gender and age were selected, the data thus consisting of 11 trios of pigs. Two of the pigs in each trio originated from the same pen: one tail biter (TB) and one tail biting victim (V). A control (C) pig was selected from a pen without significant tail biting in the same farm room. We found an effect of tail biting behavioral phenotype on the metabolism of serotonin and dopamine, with a tendency for a higher 5-HIAA level in the prefrontal cortex (PFC) of TB compared to the other groups, while V pigs showed changes in both serotonin and dopamine metabolism in the striatum (ST) and limbic cortex (LC). Trp:BCAA and Trp:LNAA correlated positivelywith serotonin and 5-HIAA in the PFC, but only in TB pigs. Furthermore, in both ST and LC, several of the neurotransmitters and their metabolites correlated positively with the frequency of bites received by the pig. This is the first study indicating a link between brain neurotransmission and tail biting behavior in pigs with TB pigs showing a tendency for increased PFC serotonin metabolism and V pigs showing several changes in central dopamine and serotonin metabolism in their ST and LC, possibly due to the acute stress caused by being bitten.
Reference: Valros, A., Palander, P., Heinonen, M., Munsterhjelm, C., Brunberg, E., Keeling, L., & Piepponen, P. (2015). Evidence for a link between tail biting and central monoamine metabolism in pigs (Sus scrofa domestica). Physiology & Behavior.