Stress Measures in Tail-biters and Bitten Pigs in a Matched Case-control Study07 August 2013
A new Scandinavian study shows that tail-bitten pigs suffer a combination of chronic stress, pathology and suppressed triiodothyronine hormone secretion, while unaffected pigs in the same pens appear to develop better coping mechanisms than the tail-biters and the victims.
In the journal, Animal Welfare, Camilla Munsterhjelm at the University of Helsinki in Finland and co-authors there and at the Swedish University of Agricultural Sciences report a recent study aimed at identifying differences in stress measures in pigs with different roles during a tail-biting outbreak.
Quartets (n=16) of age- and gender-matched fattening pigs including a tail-biter (TB; n=16), a victim (V; n=16), a control in the same pen (Ctb; n=10), and one in a pen without tail biting (Cno; n=14) were chosen by direct behavioural observation.
Stress measures used were behaviour (dog-sitting, sniffing of pen-mates and aggression), thyroid hormone concentration, morphology of adrenal and thyroid glands and salivary cortisol concentration sampled at 07:00, 10:00, 16:00 and 19:00h. Category (TB, V, Ctb, Cno) effects were investigated using a mixed model with replicate as subject and category as repeated effect.
Category had a significant effect on adrenal total (cortex + medulla) and cortical area, salivary cortisol at 19:00h, serum triiodothyronine (T3) and the behaviours performing and receiving sniffing.
Victims suffered from a triad of chronic stress, pathology and suppressed T3 secretion.
Evidence for stress in tail-biters, a possible cause of the behaviour, consisted of a slightly flattened day-time cortisol pattern and more performed sniffing than all other categories. Differences in evening cortisol concentration and T3 levels between the categories in the pen with ongoing tail-biting emphasise the qualities of the control animal.
These differences, conclude Munsterhjelm and co-authors, support the view that neutral pigs represent a phenotype that adopts a coping strategy leading to lower stress levels than in tail-biters and victims, despite being housed in the same pen.
Munsterhjelm C., E. Brunberg, M. Heinonen, L. Keeling and A. Valros. 2013. Stress measures in tail biters and bitten pigs in a matched case-control study. Animal Welfare. 22: 331-338. doi: 10.7120/09627218.104.22.1681