Editor's note: This article is part of TheHorse.com's ongoing coverage of topics presented at the 2012 Alltech Symposium, held May 21-23 in Lexington, Ky.
Could a chemical imbalance be responsible for the development of stereotypic behaviors in horses? According to one researcher, a dopamine modulation dysfunction is being implicated as a risk factor for stereotypic behavior development.
At the 2012 Alltech Symposium, held May 21-23 in Lexington, Ky., Sebastian McBride, PhD, researcher at the University of Cambridge in England, discussed dopamine's potential role in equine stereotypic behaviors.
Types and Development of Stereotypies
McBride said stereotypic behavior is present in about 7-9% of the horse population. Three of the most common stereotypies are:
- Cribbing (an oral stereotypy that involves the horse sucking air into his esophagus);
- Weaving (a locomotor stereotypy that involves lateral movement of the head and shifting weight back and forth on the forelimbs); and
- Stall walking (a locomotor stereotypy that involves a highly invariant movement pattern around the stall or pen).
McBride suggested that stereotypic behaviors often develop as a result of chronic stress or husbandry practices that restrict feeding, social contact, and/or locomotor activity. He said these behaviors are goal-directed and occur when a horse gets "stuck" between the appetitive (having the urge to carry out a task) and consummatory (actually carrying out the task) portions of goal-directed behaviors.
For example, horses evolved to travel miles each day. A stall-kept horse could have the urge to move about, but isn't able to carry out the task due to his stall confinement. As a result, he could begin weaving or stall walking to ease his desire for locomotion.
McBride said the development of stereotypic behaviors is dependent on his motivation level to fulfill his appetitive behavior: "The more they want to do it, the more likely a stereotypy will develop." He relayed that some researchers believe stereotypic horses are hypermotivated to carry out their urges, which is why they get "stuck" between the appetitive and consummatory phases.
He also relayed that recent research suggested stereotypic behaviors develop as a result of an underlying neurophysical mechanism relating to dopamine modulation.
Does Dopamine Fuel Stereotypies?
McBride explained that the brain's basal ganglia region is responsible for dopamine modulation; it is also responsible for learning and motivation. When the basal ganglia becomes dysfunctional, abnormalities develop, he said (when the basal ganglia is dysfunctional in humans, Parkinsons and Huntingtons diseases commonly result).
Previous research indicates that either chronic stress or psychostimulants can cause changes in dopamine modulation. McBride relayed that chronic stress for horses can results from weaning or the lack of ability to carry out specific behavioral needs (such as social contact or locomotion), which often results from living in a domestic environment.
Interestingly, McBride noted, some psychostimulants appear to affect horses, though not the same ones as humans. He relayed that horses consuming highly palatable foods, such as cereal grains or cereal grain-based concentrates, could have similar dopamine modulation abnormalities as humans administered psychostimulants, and thus prompt stereotypic behavior development. He also noted that horses consuming highly palatable foods on a regular basis appear more at risk for accelerated stereotypy development.
Once a horse develops stereotypic behavior, it's nearly impossible to reverse it, McBride said. Some management strategies he suggested include keeping husbandry practices as close to "wild" as possible, meeting the horse's behavioral needs, weaning gradually to avoid chronic stress, and avoiding regular feeding of highly palatable substances.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.