Mechanical nociceptive thresholds of dorsal laminae in horses after local anaesthesia of the palmar digital nerves or dorsal branches of the digital nerve.

The research explores the function of different nerve sets in the foot of horses regarding pain transmission. The study concluded that the palmar digital nerves (PDNs), not the dorsal branches (DBs) of the digital nerves, primarily transmit pain signals evoked by pressure in the sensitive dorsal laminae of the horse’s foot.

Objective of the Research

• This research investigated whether the palmar digital nerves (PDNs), instead of the dorsal branches (DBs) of the digital nerves, innervate the sensitive dorsal laminae of a horse’s foot.
• The researchers aimed to understand the biological mechanism of pain sensation invoked by mechanical stimulation on different regions in a horse’s foot including the dorsal laminae, bulbs of the heel, coronary band, and sole.

Research Methodology

• The study was conducted using six clinically normal mares in a crossover design.
• To assess mechanical pain boundaries, a portable dynamometer was used.
• The measurements were performed before and after the horses received perineural injections of PDNs or DBs, using either a local anaesthetic solution (in the treated group) or an isotonic saline solution (in the control group).
• For accurate measurement of the nociceptive thresholds, the cornified tissue was extracted from the sole and the dorsal aspect of the hoof wall.

Findings of the Research

• Post-anaesthesia of PDNs (distal to DBs) significantly increased the horses’ mechanical nociceptive thresholds contrasted to baseline values at all the evaluated locations, including the dorsal laminae, sole, and the bulbs of the heels.
• By contrast, anaesthesia of DBs led to an increase in pain thresholds only at the most proximal aspect of the foot, specifically the coronary band sites.

Conclusion of the Research

• The study concludes that when it comes to pain transmission due to pressure exposure on the dorsal laminae of a horse’s foot, PDNs play a predominant role rather than DBs.