Increased exposure to stress can induce long-term changes in
the regulation of the HPAaxis. Repeated exposure to stressors can
produce increases in adrenocortical function, as evidenced by
increased basal plasma corticosteroid concentrations or increased
adrenal weight [52–55]. It is generally accepted that social stress
can cause an activation of the HPA axis in pigs [56–59]. An
increase in salivary cortisol levels was associated with recipients
of ear biting and animalswith tail lesions in this study. Tail and ear
biting behavior is considered as an abnormal behavior in pigs and
the welfare of the recipient may also be poor [13,60]. The higher
levels of cortisol found in animals with tail lesions and in earbitten
animals confirm an activation of the general adaptation
syndrome [61]. Hunter et al. [62] found that pigs with bitten tails
had significantly higher levels of ear damage than pigs with
unbitten tail. In due course the biting can become more severe
resulting in wounds and hemorrhage [63]. In severe cases, the
wounded animal gradually gives up its resistance and its effort to
flee. It becomes apathetic, lies down much of the time, seldom
changes position, and reacts only slightly to being bitten. The
constantly moist tail attracts bacteria leading to inflammation
[63]. Besides the pain and the clinical symptoms involved for the
victim, this biting behavior increases the disturbance among a
pen-group. Hansen et al. [64] made clear that there is a connection
between tail biting and aggression.