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sufficiently high to allow further selection against fearfulness (
Boissy et al.,
2005a
). Observed heritabilities also revealed a genetic component in calf reactiv-
ity (behavior, heart rate, cortisol) to a fear test; fearful calves became fearful hei-
fers, and high fearfulness and a poor milking temperament were associated with
low milk yield (
Jones and Manteca, 2009
;
Van Reenen et al., 2005; 2009
). For a
further discussion of the genetic aspect of fearfulness, see the section on
Genetics and Selective Breeding for Alleviating Negative Emotions.
Developmental Aspects
While there is a strong genetic component to fearfulness, the environment
plays a very important role as well. The role of the prenatal environment for
the development of farm animals has recently been reviewed (
Roussel et al.,
2007; Rutherford et al.,2012
). The role of the hypothalamus
adrenal
axis is of particular interest (
Kapoor et al., 2006; Matthews, 2002
). The main
aspects are maternal stress and nutritional state during pregnancy, and the
effects depend on the severity of the stressor as well as on the developmental
stage of the fetus and the time of the stressor. Peri-conceptional undernutrition
in sheep (
Hernandez et al., 2010
), as well as undernutrition in early (
Erhard
et al., 2004
) and late gestation (
Laporte-Broux et al., 2012
), can affect the
development of fearfulness in the offspring to affect them throughout their
lives. Mammals are not the only ones affected by prenatal stress. Maternal
stress in birds (i.e. pre-egg laying) results in more fearful offspring (
Henriksen
et al., 2011; Janczak et al., 2007
). Even in farmed fish (salmon), there is evi-
dence for the deleterious effects of maternal stress on the development of the
offspring (
Eriksen et al., 2011; Espmark et al., 2008
).
The development of fearfulness does not end at birth. More fearful quail,
for instance, can still increase their chicks' fearfulness post-hatching (
Richard-
Yris et al.,2005
). There are periods when young animals are specifically
sensitive to long-term changes in fearfulness, for instance around weaning
(
Lansade et al.,2004
).
pituitary
Personality and Health
There is evidence of a link between personality and health in animals
(
Koolhaas, 2008; Mehta and Gosling, 2008
). Individuals scoring high on
emotional reactivity and fearfulness are more easily stressed and, as a conse-
quence, may have a weaker immune system. For instance, fear-related reac-
tions to humans in cattle entering a feedlot are negatively associated with
immune function (
Fel et al., 2003
). The reality can, however, be more com-
plicated. Pigs that react more actively to restraint-stress at a young age, show
a stronger immune response several weeks later, compared to counterparts
that are less active to the restraint test. The latter, however, seem to be more
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