The influence of various confounding factors on mechanical nociceptive thresholds in the donkey.

This research evaluates a mechanical nociceptive threshold (MNT) testing device in donkeys and investigates the influence of several confounders on MNT. The study found that the application rate of force must be standardized in MNT studies in donkeys and indicated a good short-term stability with greater long-term variability.

Study Methods and Participants

• The study involved a set of sixteen castrated male donkeys that were aged between 4-9 years and weighed between 105-170 kg.
• Mechanical nociceptive thresholds were measured using a device consisting of an actuator with three pins placed on the upper side of the donkey’s lower leg and connected to a force meter.
• The pins were forced onto the limb by pressurizing an air-filled syringe until the MNT force was reached or a 25 N cut-off force was hit. The MNT force recognized is the force at which a foot lift is observed.
• The influence of several factors was studied including the presence of a companion donkey, the limb being tested, the rate of application of force, the testing location, the level of distraction, the ambient room temperature, and hair cover at the test site.
• The long and short-term repeatability of MNT was also taken into consideration. The data were analyzed using general linear models and Mann-Whitney U tests with p < 0.05 considered as significant.

Study Findings

• The results showed that increasing the rate of force application significantly increased the mean MNT. The average MNT increased from 9.2 ± 2.0 N when applied at 0.4 N sec(-1) to 10.6 ± 2.1 N when applied at 1.2 N sec(-1).
• None of the other factors (presence of companion donkey, limb tested, testing location, level of distraction, ambient temperature, hair cover at the test site) significantly influenced the MNT.
• On the issue of stability, the mean MNT remained stable over a 3 week period, but it was significantly higher after a 12-month interval.

Study Conclusions

• From this study, it was concluded that when designing studies measuring MNT in donkeys, the rate of application of force needs to be standardized.
• The research suggested that this technique is appropriate for short-term analgesiometry studies due to the good stability of donkeys’ MNTs in the short-term. However, there was significant variability of MNTs over the long-term.