Does duration of farrowing affect plasma oxytocin concentrations of sows at the subsequent oestrus?

Introduction: Previous studies showed that prolonged farrowing could lead to decrease in fertility rate at the subsequent oestrus in sows. Oxytocin is wellknown
for its role in myometrial activity and reproduction process in oestrous sows. We, therefore, investigated whether duration of farrowing affects
plasma oxytocin concentrations of sows at subsequent oestrus.
Materials and Methods: A total of 31 crossbred sows (Finnish Yorkshire × Finnish Landrace) were allocated two treatment groups according to duration of
farrowing: 1) SHORT (159 ± 29 min): 14 sows (parity 3.8 ± 2.6) with shorter than 200 min farrowing duration, and 2) LONG (579 ± 263 min): 17 sows (parity
5.1 ± 2.5) with longer than 300 min farrowing duration. Duration of farrowing was determined by the birth interval between the first and the last piglets. After
a 4 week lactation, the sows were confined in the stalls and catheterized three days before the expected oestrus through the auricular vein following a
nonsurgical catheterization procedure. Upon triggering the standing reflex by boar introduction, blood samples were collected -15, -10, -5, 0, 1, 2, 3, 4, 6, 8,
10, 15, 20, 25, 30, 40, 50 and 60 minutes while the boar introduction occurred at 0 min. Plasma oxytocin concentrations were measured using ELISA kits
(Enzo Life Sciences, Switzerland). Repeated measures using mixed model were used to analyze periodical oxytocin concentrations according to the boar
introduction.
Results: Plasma oxytocin concentrations of oestrous sows in the LONG group (22.2 ± 1.8 pg/ml) were greater than in the SHORT group (15.6 ± 2.0 pg/ml)
during the whole sampling period, i.e. 15 min prior to until 60 min post boar introduction (P < 0.05). During the presence of the boar for 10 min, oestrous
sows in the LONG group (27.8 ± 3.6 pg/ml) tended to have greater plasma oxytocin concentrations than in the SHORT group (17.8 ± 4.0 pg/ml; P = 0.07).
Conclusion: The results indicate that prolonged farrowing might lead to an increase in plasma oxytocin concentrations of oestrous sows at the following
breeding. However, further research is needed to demonstrate interrelationship between duration of farrowing, oxytocin concentrations during estrus, and
follicle development in sows.