Spontaneous electroencephalographic changes in a castration model as an indicator of nociception: a comparison between donkeys and ponies.
Authors: Grint N J, Johnson C B, Clutton R E, Whay H R, Murrell J C
Journal: Equine veterinary journal
Summary
# Editorial Summary Donkeys have long been perceived as stoic animals less prone to displaying pain than ponies, yet the neurophysiological basis for this behavioural difference remained unclear. To investigate whether donkeys and ponies process noxious stimuli differently at the cortical level, Grint and colleagues recorded electroencephalographic (EEG) activity in six animals of each species during castration under general anaesthesia, marking discrete time points at skin incision and emasculation for each testicle. Although EEG responses varied considerably between individuals, donkeys showed significantly greater reductions in total power (P = 0.004) and greater increases in spectral edge frequency (P = 0.05) at the first skin incision compared with ponies—findings that indicate a more pronounced cortical response to noxious stimulation rather than a diminished one. These results suggest that donkeys' characteristically subtle behavioural expression of pain does not reflect reduced sensory processing or pain perception, but rather reflects a genuine species difference in how pain is *communicated* behaviourally, which has important implications for pain assessment and welfare monitoring in clinical and management settings where relying solely on visual signs could underestimate a donkey's discomfort.
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Practical Takeaways
- •Donkeys' apparent stoicism during castration does not reflect reduced pain perception at the cortical level; assume they experience pain similarly to ponies and provide appropriate analgesia
- •EEG-derived measures like total power and spectral edge frequency may help objectively assess pain responses in equines when behavioral indicators are subtle or unreliable
- •The species difference in pain expression appears behavioral rather than neurophysiological, suggesting differences in pain coping strategies rather than nociceptive processing
Key Findings
- •Donkeys showed significantly greater decrease in total power (Ptot) at skin incision compared to ponies (P = 0.004), indicating a more pronounced cerebral response to noxious stimulus
- •Donkeys demonstrated greater increase in spectral edge frequency (F95) at first skin incision relative to baseline compared with ponies (P = 0.05)
- •Electroencephalographic responses to castration noxious stimuli were observed in both species, with donkeys showing similar or greater cortical activation than ponies
- •Donkeys' subtle behavioral expression of pain during castration is not attributable to reduced cortical processing of noxious sensory stimuli