Behavior Genetics of the Horse (Equus caballus) - Genetics and the Behavior of Domestic Animals - page 274

24 radial (no rotation). The foals were tested 50 times each using the first
step described by Murphy et al. (2005) . Results showed no association
between hair whorl rotation and asymmetry, but did find that males were
more left-lateralized, and foals with radial whorls were more balanced (ambi-
dextrous). These results contradict those obtained by Murphy et al. (2005) ,
and the difference in results may be caused by the difference in the age
groups. The yearling foals studied by Ovando (2010) were all the same age
and received halter training but otherwise minimal contact with humans. The
horses studied by Murphy et al. (2005) were all trained to ride. This finding
is in agreement with McGreevy and Roger (2005) who found that horses
under 2 years of age were less lateralized, compared with a higher percentage
of left lateralized horses over 2 years old. It may be that the “motor” lateral-
ity observed in ridden horses is actually motor asymmetry influenced by sen-
sory laterality influenced by stress induced by training and riding. It is recog-
nized that the amount of psychological stress (fear) that an animal encounters
determines the degree of response of the hypothalamic adrenal

(HPA) axis ( Cayado et al., 2006 ). Blood samples collected in Dressage and
Jumping horses at their familiar home environment were compared to samples
taken before exercise, at the entrance to a schooling area, and post perfor-
mance over jumps or a dressage course. Plasma cortisol and plasma ACTH
were highest in the least experienced horses, high in horses with intermediate
experience, and slightly lower in the most experienced horses ( Cayado et al.,
2006 ). The fear responses in the most experienced horses were attenuated, but
still evident.
The inconclusive results of hair whorl direction in horses and asymmetry
are similar to the inconclusive results of studies of hair whorl rotation and
handedness in humans ( Beaton and Mellor, 2007 : Jansen et al., 2007; Klar
2003; Weber et al., 2006 ). In addition, all these studies only focus on whorl
rotation (e.g., clockwise, counter-clockwise) and laterality—not whorl place-
ment and laterality. Anecdotal evidence presented by the first author suggests
that hair whorl position (e.g., left or right of midline) is a more reliable pre-
dictor of laterality in horses. Support for this anecdotal evidence was recently
reported by Tomkins et al. (2012) in dogs. Specifically, the location of a
whorl on the left side of a dog's head and neck was associated with a right
visual bias, and a right visual bias was also probable if the hair whorl on the
ventral mandibular (back of the bottom jaw) was present in a counter-
clockwise direction. The study assessed all three measures of laterality (hair
whorl, motor, and sensory) in Labrador retrievers, golden retrievers, and
Labrador

pituitary

golden retriever crosses. The dogs were prospective guide dogs
for the blind provided by Guide Dogs NSW/ACT. Dogs' performances on
the Kong

test, the First-Stepping Test, and the Sensory Jump Test deter-
mined motor and sensory laterality. Several associations emerged between
hair whorls and motor and sensory laterality. The authors suggest that hair
whorls may provide a quick and efficient means of determining suitability in

t