Biology Reference
In-Depth Information
Pigs' Ability to Handle Stress
Many studies of stress in pigs have been performed, but the motives have
often been more related to meat quality than to pig welfare. The genetic
selection for high production has probably contributed to a reduction of HPA
axis activity and consequently to a decreased capacity of modern, high-
producing animals to maintain their production despite of environmental
changes (
Morm
`
de and Terenina, 2012
). The acute response of the HPA axis
can be studied by monitoring the release of ACTH, and cortisol levels are
often used to measure chronic stress when assessing animal welfare
(
Wiepkema and Koolhaas, 1993
). The stress response, measured by the
response to ACTH, is heritable. Gene expression studies (
Hazard et al.,
2008; Jouffe et al., 2009
) have indicated candidate genes for differences in
ACTH response. But the association between ACTH response and behavior
is seldom investigated.
D´saut´s et al. (1997)
showed that Large White pigs
had higher post-stress ACTH levels than Meishan pigs after an open-field
test. They also showed significant correlations between vocalization and
locomotion scores and post-stress ACTH levels, suggesting that these mea-
sures reflect the level of reactivity to the environmental challenge, and that
they may have a common genetic background.
Engelsma et al. (2011)
used the open-field test and found that sows with
higher breeding values for piglet survival were more explorative; they
manipulated the floor and the walls for a longer time than sows with low
breeding values. In a small study where Meishan (MS) and Large White
(LW) gilts were compared, a test series including the reaction in an open-
field test (5 minutes of exploration), the reaction to a novel object (a bucket
descended from the ceiling and left on the floor for 5 minutes), and finally
the reaction to an unfamiliar human entering the open field and standing
there motionless for 5 minutes was used (
Canario et al., 2009
). In the first
challenge, the MS females that stand motionless were the ones with the high-
est litter growth later on. The LW females that explore less were the ones
with the lowest stillbirth rate and piglet mortality later on. In the last chal-
lenge, the MS gilts which remained standing all the time had higher piglet
growth and the LW gilts that showed higher latency to first move had higher
piglet survival. Thus, gilts' ability to handle stressful situations determines
their maternal ability later in life but these relations differ between breeds.
Low ability to handle stress, so called Porcine Stress Syndrome (PSS) is
caused by a mutation in the locus for the ryanodyne receptor gene RYR(1)
and the mutated allele, n, is recessive. It is associated with high leanness and
high susceptibility to the development of stress. Stressful stimuli trigger a
potentially lethal condition known as malignant hyperthermia in homozygous
nn pigs and the n allele has been eradicated from several populations. In
some sire-line populations, the n allele is still regarded as a resource, due to
its association with leanness. Since all crossbred pigs raised for slaughter are
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