CLASSICAL COUNTER CONDITIONING PROMOTES A POSITIVE AFFECTIVE STATE DURING A NERVE BLOCKING PROCEDURE IN A RANDOMISED, BLINDED CLINICAL TRIAL

Lameness is the most common health problem in the UK equine population and nerve blocks are commonly performed to localise the source of pain. However, the nerve block procedure can be stressful for the horse and veterinarians are at significantly increased risk of sustaining injuries such as a fracture, unconsciousness or hospitalisation compared to other veterinary procedures. The aim of this study was to determine whether classical counter conditioning (CCC) during the preparation phase would positively influence a horse’s perception of a nerve block. Cases (n=27) presenting for lameness investigation were recruited and randomly assigned to CCC (n=13) or control (n=14) groups. The CCC group were trained to associate a person approaching their limb with the provision of food during the preparation phase. The control group received no training. The handling of the horse during the nerve block was at the discretion of the veterinarian performing the procedure. Horses were filmed during the nerve block and these segments were evaluated first, using a quantitative ethogram and second, using Qualitative Behaviour Assessment (QBA), with a fixed term list, in a randomised order by 5 independent observers blinded to treatment group. Physiological data were also collected but not presented. QBA scores were subject to principal component analysis (PCA). The 1st PCA explained 33% of the variation and was considered to represent affective state. Linear mixed effects regression models were then performed on the factor scores from the 1st PCA to determine significant relationships with multiple variables. The model of best fit included the following independent variables: observer, limb, block number, type of block and veterinarian, with segment number and horse ID as random effects. In this model horses in the CCC group were scored as being in a significantly more positive affective state then controls (estimate=0.63, SE=0.253, t.ratio=2.49, p=0.02). The CCC group also received more nerve blocks (2.7 per horse) than controls (1.7). The quantitative behavioural data had a weak but significant association with the PCA factor scores (Spearman rho=0.118, p=0.042). In summary, CCC can be used to produce a more positive affective state when performing nerve blocks. Further investigation is now needed to determine if this results in fewer occupational injuries sustained during this procedure and how else quality of life can be optimised in horses undergoing veterinary care.
Lay person message: A nerve block is commonly used to determine the source of pain in lame horses and can be stressful for horses and may result in injury of the veterinarian. By pairing the approach to the horse’s leg with offering food, during the preparation phase the horses were scored as being in a more positive emotional state during the nerve block than horses who did not have food associated with preparation for the nerve block procedure. This may reduce occupational injuries and optimise equine quality of life during veterinary care.
Keywords: classical counter conditioning; nerve block; veterinary; equine; emotional state, welfare