Behavioral Genetics in Pigs and Relations to Welfare - Genetics and the Behavior of Domestic Animals - page 419

heterozygote the problems of stress sensitivity and mortality are mainly seen
in the purebred sire line. Even so, according to Murray and Johnson (1998)
Nn pigs also die more often during transport than NN pigs. Furthermore, Nn
pigs are less active than NN pigs in an open-field test ( F`brega et al., 2004 ).
Under commercial conditions, no behavioral differences were found between
NN and Nn pigs of various ages in traits like frequency of resting, non-
suckling activity, suckling/eating activity and social interactions ( F`brega
et al., 2005 ). The example of the halothane gene is interesting, because it
was one of the first major genes that could be used in breeding programs.
Some breeding organizations decided to refrain from the n allele and its high
leanness due to welfare reasons as long ago as the 1980s, while other breed-
ing organizations still use the n allele without ethical concerns.
Terlouw et al. (1997) and her colleagues have compared different breeds
with regard to behaviors that reflect the ability to feel or cope with stress as
well as stress hormone levels and meat quality. Duroc pigs touched humans
more often than Large White pigs did in a human-exposure test. However,
when doing so, the Duroc pigs had higher heart rates than the Large Whites.
Touching the man or not in the test depends on the fear the man induces in
the pig and the pig's motivation to have contact with the man. It is not
known whether the Durocs were less fearful or more motivated to touch the
man as compared to Large Whites. Anyway, the response in this test (heart
rate) had less effect on meat quality in Durocs than in Large Whites.
Terlouw (2005) concludes that the impact of stress response on meat quality
is breed dependent. Maybe the same is true for the impact of stress response
on welfare?

FREEDOM TO EXPRESS NORMAL BEHAVIOR
In the fifth freedom of FAWC (1992) it says that animals should have the
freedom to express “normal behavior”. In line with that, demands for the
ability to express normal or natural behavior are found in animal welfare
laws, and in organic farming natural behavior is a key issue ( Lund et al.,
2004 ). The Swedish Animal Welfare Act (1988) , for example, states that
“Animals shall be accommodated and handled in such way as to

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permit natural behavior.” The international standards for organic animal hus-
bandry state that “systems that change from conventional to organic produc-
tion require a conversion period to develop natural behavior” and that
“organic livestock husbandry is based on

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respect for physiological and
behavioral needs of livestock” ( IFOAM, 2005 ). In a resolution adopted in
1999 by the Federation of Veterinarians of Europe (FVE) it says that
selected animals “may be unable to express their natural behavior”. The defi-
nition of natural behavior of domestic animals is, however, problematic. Are
all behaviors performed by wild boars “natural” for domesticated pigs?
Segerdahl (2007) proposes that natural behavior of domesticated animals is a

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