Behavioral Genetics and Animal Science - Genetics and the Behavior of Domestic Animals - page 21

objects improves learning and results in increased growth of dendrites (nerve
endings in the brain).
Pigs raised in barren concrete pens also actively seek stimulation ( Grandin,
1989a,b; Wood-Gush and Beilharz, 1983; Wood-Gush and Vestergaard, 1991 ).
Piglets allowed to choose between a familiar object and a novel object prefer
the novel object ( Wood-Gush and Vestergaard, 1991 ). Pigs raised on concrete
are strongly attracted to objects to chew on and manipulate. The first author
has observed that nervous, excitable hybrid pigs often chew and bite vigor-
ously on boots or coveralls. This behavior is less common in placid genetic
lines of pigs. Although hybrid pigs are highly attracted to novelty, tossing a
novel object into their pen will initially cause a strong flight response.
Compared to calm genetic lines, nervous-hybrid pigs pile up and squeal more
when startled. Pork producers report that nervous, fast-growing, lean hybrid
pigs also tail-bite other pigs more often than calmer genetic lines of pigs (see
Chapter 11). Tail biting occurs more often when pigs are housed on a concrete
slatted floor which provides no opportunity for rooting.
Practical experience by both authors suggests that highly reactive horses
are more likely to engage in vices such as cribbing or stall weaving when
housed in stalls or runs where they receive little exercise. Denied variety and
novelty in their environments, highly reactive animals adapt poorly compared
to animals from calmer genetic lines ( Huck and Price, 1975 ).
In summary, in both wild and domestic animals, novelty is both highly
feared and necessary. Novelty is more desirable when animals can approach
it voluntarily. Unfortunately, novelty is also fear-provoking when animals are
suddenly confronted with it.
Temperament is Not Just About Fear
Early research showed that animals as diverse as rats, chickens, cattle, pigs, and
humans, genetic factors influence differences in temperament (fearfulness)
( Royce et al.,1970 ; Bilzard, 1971; Broadhurst, 1975; Fordyce et al., 1988;
Fujita et al., 1994; Grandin, 1993b; Hemsworth et al., 1990; Kagan et al., 1988;
Murphy, 1977; Murphey et al., 1980a; Reese et al., 1983; Tulloh, 1961 ).
Trillmich and Hudson (2011) suggest that a broader area of animal personality
needs to be studied. Today the concept of temperament includes all the neuro-
transmitter systems that affect the strength of different emotional systems. Barr
(2012) contains an outline of how behaviors such as fear and exploring are
affected by different neurotransmitter systems. Some individuals are wary and
fearful and others are calm and placid. Boissy (1995) stated, “fearfulness is a
basic psychological characteristic of the individual than predisposes it to per-
ceive and react in a similar manner to a wide range of potentially frightening
events.” In all animals, genetic factors influence reactions to situations which
cause fear ( Boissy and Bouissou, 1995; Davis, 1992; Kagan et al., 1988;
Murphey et al., 1980b ). Therefore, temperament is partially determined by an