By Mark Andrews

A toxin extracted from shellfish shows promise as a safe and effective long-lasting treatment for horses with bucked shins.

Neosaxitoxin is produced by photosynthesis in phytoplankton and cyanobacteria. It may be concentrated by shellfish, and is one of the toxins responsible for Paralytic Shellfish Poisoning (PSP). It blocks nerve transmission by reversibly binding to receptors in sodium channels, and can be fatal if ingested.

Bucked shins (dorsal metatarsal disease) is a painful, acute periostitis of the dorsal surface of the third metacarpal bone. It is seen most commonly in the forelimbs of young Thoroughbreds (two-year-olds) in training and racing.

Neosaxitoxin has been used as a long-acting analgesic in human medicine. Would it be effective as a long-lasting analgesic in horses with bucked shins? 

Gricel Riquelme and co-workers in the Membrane Biochemistry Laboratory, Department of Physiology and Biophysics, Faculty of Medicine, University of Chile, Independencia, investigated.

They assessed the response in 14 horses diagnosed with bucked shins, from Club Hípico Racetrack in Santiago, Chile.

Horses were treated with one of three concentrations of neosaxitoxin injected under the skin at the top of the affected metacarpal. The research team assessed the response by monitoring lameness and noting the sensitivity of the affected area to pressure.

They found a significant improvement in pain, measured both by the abolishing of lameness and an increase in the pressure tolerated before lifting the leg. The duration of response was dose dependent, with administration of 600 micrograms being effective for up to three weeks.

The researchers conclude that neosaxitoxin infiltration provides safe and effective pain control in bucked shins without adverse side effects.

Photo: shutterstock_2095485 - Tina Rencelj

Printed with permission of Mark Andrews, Equine Science Update.

This article was originally published in Canada’s Equine Guide 2018, a publication of Canadian Horse Journal.