Behavior Genetics of the Horse (Equus caballus) - Genetics and the Behavior of Domestic Animals - page 275

prospective guide dogs because a need to work on the left side of trainers
often disqualifies dogs that are less flexible when turning right. It also takes
a significant amount of time to train guide dogs. The dogs must learn several
complex tasks, and it is important to find a quick and efficient means of dis-
covering traits in the early stages of training that decide whether a dog will
be a successful guide dog.
Clearly, further research is needed to determine associations between hair
whorl direction and laterality in horses. Lateralization is important because
it is related to locomotion and subsequent performance during training.
Determining lateral trends at a glance could be very useful for designing
individual training programs.
Chronic Asymmetry
In his experiences as a horse trainer, the first author has faced several one-
sided horses. In some horses, the turning preference was so strong that any
attempt to change it caused the horse to prance, throw its head, or rear. Any
use of force to change a preference was likely to cause a panic-like response.
To our knowledge, no scientific research into the cause of extreme laterality
in horses exists; however, various explanations of extreme one-sidedness exist
in the popular horse-training literature. The most often-cited reasons are
strong motor asymmetry or pain. Lateralized behavior is undesirable in
various equitation disciplines, and persistent lateralized behavior has not
been thoroughly investigated. Scientists and industry professionals rarely
discuss fear as a possible cause of extreme one-sidedness. All the same,
evidence of brain asymmetries previously discussed point to many lateral
behaviors associated with fear responses. Fearfulness may be more common
in horses than is generally assumed. Horses do not require many fearful
experiences for fear behavior to be habitually expressed, and many chronic
fear behaviors in animals and humans can be traced back to a single event
( Lindsay, 2000 ). One-trial-learning of fearful responses is documented in
horses ( Kiley-Worthington, 1987 ). Fear responses are learned at the subcorti-
cal level involving the amygdala and hippocampus ( LeDoux, 1998 ), with
direct projections to the motor cortex. Lateral behavior and hair whorl side-
position has been demonstrated in cattle ( Tanner et al., 1994 ), and fear
responses are associated with hair whorl height-position in cattle ( Grandin
et al., 1995; Silveira Dias Barbosa et al., 2006 ), and horses ( Gorecka-Bruzda
et al., 2007 ). Although hair whorl side-position and lateral fear responses have
yet to be demonstrated in horses, anecdotal evidence collected by the first
author suggests an association between lateralized fear responses and the side
position of hair whorls in such things as handling feet, lunging in circles,
riding, reining, trailer loading, and jumping. Left-side hair whorls predict left-
side resistance to horseshoeing, and predict a preferred rightward direction of
travel when working in circles. In many cases, these lateral behaviors are