Effects of stress on maternal
behaviour in pigs
J. Rushen1, A.M. de Passille1,
J. Ladewig2 and G. Foxcroft3
1Agriculture and Agri-food
Canada, Lennoxville, Canada; 2Animal Husbandry & Behaviour, Trenthorst,
Germany, and
3University of Alberta,
Edmonton, Canada
Little is known of how
stress affects maternal behaviour in pigs. Many nursings are unsuccesful
and piglets get no milk. Stress is often considered the cause, but there
is little evidence. We examined if lactating sows in novel environments
have more unsuccessful nursings. Six sows (3-14d postpartum) were either
placed with their piglets for 2h in a different farrowing pen, or were
driven into the new pen and immediately returned to their own (control).
All sows were subject to both treatments over two days, with the order
of treatments being balanced. Nursings were recorded as successful if there
was increased rate of grunting by the sow and rapid sucking by the piglets.
Blood was sampled every 10 min and assayed for ACTH and cortisol. Placing
the sow in the novel pen did not significantly increase the latency to
the first nursing attempt, but the proportion of nursings that failed was
much higher (51% versus 8%, P<.01), and the latency to the first successful
nursing was longer than in the home pen (P<.01). Cortisol and ACTH concentrations
were not ncreased in the novel environment (P>0.10), and neither cortisol
nor ACTH were higher before an unsuccessful nursing than before a successful
one (P>0.10). An unfamiliar environment increases the chance that a nursing
will fail to lead to milk ejection, thus demonstrating that some unsuccessful
nursings result from stress, but the effect is not mediated by hypothalamo-pituitary-adreno-cortical
(HPA) activity, throwing doubt on the value of this traditional index of
stress. To
determine the role of
opioid peptides in stress-induced inhibition of nursing, 10 sows (3-7d
postpartum), had their piglets removed for 2h, and were treated as follows.
1. No treatment, 2. Nose-snare restraint for 20 min., 3. Naloxone injections
(i.v. 2mg/kg), 4. Snare + naloxone. After the treatment, the piglets were
returned, milk ejections were timed, and the sows' blood sampled every
10 min. for cortisol, GH and prolactin assays. Restraint increased cortisol
(P<.05) but did not delay the first milk ejection or reduce the frequency
of nursings. No unsuccessful nursings were observed and successful milk
ejections occurred when cortisol levels were elevated. Piglet removal increased
cortisol and decreased prolactin and GH (P<.05). The rise in GH when
piglets were returned was prevented by the combination of restraint and
naloxone, but not by restraint alone. Opioids protect lactogenic hormones
against behavioural stress, but stress-induced HPA activity does not inhibit
milk ejection in the pig. Stress is often considered a nonspecific HPA
reaction to environmental challenges but the concept should be broadened
to include specific disruptions of biological functions via other neuroendocrine
pathways.