Behavior Genetics of the Horse (Equus caballus) - Genetics and the Behavior of Domestic Animals - page 236

familiar arena. Each horse was released into the arena and behavior was
recorded (locomotion, gazes, approaches) for 5 minutes. A bridge test was
used to estimate fearfulness. A foam mattress covered with checkered cloth
(called a bridge) was placed in the familiar arena. Each horse was led to the
bridge with a halter and the experimenter tried to encourage the horse to
cross the bridge. For the learning and memory task, each horse learned how
to open a wooden box with food inside, and subsequently it had to remember
how to open the box 12 hours later. Given the fact that each test was
designed to measure different facets of personality, the results of this study
are extremely interesting. The results showed that genetic factors, such as
sire or breed, influenced more neophobic reactions (fear of new things or
experiences) such as the bridge test. On the other hand, environmental fac-
tors, such as type of work, played a more dominant role in learning abilities
and reactions to social separation. Show and dressage horses exhibited higher
emotional reactions to the social isolation test and the fear test (bridge) com-
pared to horses used for other types of work. This is a notable finding, since
a prior study also found a high level of stereotypies in dressage horses
( McGreevey et al., 1995 ). Furthermore,

environment
effects uncovered are especially significant. In simple terms, additive effects
mean that the expression of genes is influenced by differences in the envi-
ronment. For example, the 98 breeding stallions tested in this study were
stabled in two government facilities and kept under similar conditions
(food, stall, little or no training for riding). The breeds were similar in both
facilities, but environmental differences between the two facilities added to
differences in the reactions to the bridge test (fearfulness), and the stallion's
ability on the memorization test. The researchers suggest that varying
handling practices and differences in caretaker behavior probably caused the
differences in the behavior of the stallions in the two facilities.
Together, these two studies emphasize how far equine behavior science
has come since the first edition of this topic was published. The remaining
sections cover additional studies on: the effects of early experience on
behavior; the difficulties associated with finding easy ways to predict
temperament; the relationship between hair whorls and behavior; and lateral-
ization in the nervous system. The emphasis in each section will focus on
interactions between the genetic and environmental effects on behavior.

the additive gene

THE EFFECTS OF EARLY EXPERIENCE ON BEHAVIOR
Variability in emotional reactivity between animals is a phenotypic trait
defined as temperament ( Boissy, 1995 ). Horse breeders know that some foals
are fearful and sensitive, while others are bold and confident. A variety of
terms are used to describe temperamental differences in animals, but for
simplicity the authors use the term “reactive” to describe animals that are
flighty, nervous, or highly emotional. The term “low-reactive” is used to