Boar contact does not induce oxytocin release during the period of embryo migration in sows

Nine multiparous cyclic sows with permanent jugular catheters were introduced to a boar at day 10 (n = 9) or 11 (n = 5) after ovulation to study the effect on oxytocin (OT) release. If it occurs, the release of OT might play a role in embryo migration which occurs around this time, by stimulating uterine contractions. Blood samples were taken before introduction of the boar and at 2-min intervals up to 10 min after boar introduction. On average, OT levels after boar introduction were not higher than before. In only three out of the 14 occasions of boar introduction, a rise in OT level was observed that was higher than two times the standard deviation above base level. However, even on these occasions OT levels were far below the range normally observed during other events where exogenous stimuli cause OT release, such as boar introduction during estrus and suckling during lactation. We conclude that boar contact around day 10 of the estrous cycle does not induce a biologically significant OT release in sows.