Behavior Genetics of the Horse (Equus caballus) - Genetics and the Behavior of Domestic Animals - page 251

GENETICS AND TEMPERAMENT: ORIGINS AND OUTCOMES
Temperament is defined as differences in behavior between individuals that
are consistently displayed when tested under similar situations ( Hausberger
et al., 2004; Kagan, 2005; Plomin and Daniels, 1997 ; Zentner and Shiner,
2012 ). Most scientists agree that temperament consists of early-appearing,
biologically based behavior patterns that originate in the horse's biology and
appear early in development. The biological foundation is usually genetic,
but may be a result of prenatal events. Young horses show considerable
variation in temperament (e.g., fearfulness, sociability, reactivity, etc.).
Fearfulness is probably the most important factor influencing the suitability
of horses for any type of work. Fearfulness is defined as the general propen-
sity of an individual to perceive and react in the same manner to a wide vari-
ety of potential threats ( Boissy, 1998; Christensen, 2006 ). Abundant evidence
demonstrates that past environmental factors and previous experience have a
significant effect on fearfulness. Repeated exposure to stimulus early in life
can modulate the development of subsequent fear reactions. Exposing a fear-
ful young horse to an enriched environment and gentle handling procedures
may reduce subsequent fear-related reactions. On the other hand, exposing a
less fearful horse to a stressful environment and rough handling increase sub-
sequent fear related reactions. Early stimulation and later experience interact
throughout the horse's life with the genetic background ( Christensen, 2006 ).
The ability to select a horse for a particular type of work, especially from a
very young age, is an attractive idea for breeders, trainers, and horse enthu-
siasts. Behavior tests have been developed to identify temperament traits, but
a factor that is usually overlooked is the biological basis of the traits being
investigated. For example, by the time a horse is old enough to begin train-
ing for riding, it is difficult to detect the biological basis of temperament
because the behaviors measured at this time could be a product of experience
alone. Not all fearful horses inherit the biological basis of that trait. The
origin of temperament has a genetic basis, but the outcome is influenced by
environment and upbringing.
A central question in studies of temperament is whether an individual's
temperament traits remain consistent over time ( Visser et al.,2001 ). In addi-
tion, the age at which temperament can be considered stable is still
debatable ( Seaman et al., 2002 ). The reliability of temperament tests of older
horses is hindered by the fact that the background is usually unknown and
the behavior is more influenced by previous experience. Thus, previous
experience may have more influence on responses measured in standardized
behavioral tests than any underlying genetic influence. Previous experience
affects older horses more than younger horses. In addition, previous experi-
ence may influence responses in a familiar setting, whereas response to nov-
elty in an unfamiliar setting may better reflect horses' underlying reactivity
(temperament). Standardized behavioral observations that depend on the