The effect of litter size, parity and farrowing duration on placenta expulsion and retention in sows

The hypothesis was that a prolonged parturition impairs placenta expulsion and can lead to retained placentas in sows. Furthermore, we hypothesized that application of oxytocin around the time of expulsion of the first placental part improves placenta expulsion. We recorded 142 parturitions of 101 Yorkshire x Large White sows. We determined parity, gestation length, number of liveborn and stillborn piglets, farrowing duration (time between first and last piglet) and the outcome variables: number of expelled placental parts, placenta expulsion duration (time between first and last placental part), first placental part expulsion (time between last piglet and first placental part) and last placental part expulsion (time between last piglet and last placental part). The relationship between farrowing duration and each of the outcome variables was investigated using four distinct multivariable models. Use of oxytocin (used in 44 out of 142 parturitions) increased number of expelled placental parts (3.8 ± 0.2 vs. 2.9 ± 0.3; P = 0.035), decreased the placenta expulsion duration (172 ± 44 vs. 328 ± 26 min; P = 0.011) and time of last placental part expulsion (148 ± 48 vs. 300 ± 24 min; P = 0.025). If oxytocin was not used, farrowing duration obeyed a quadratic relationship with the number of expelled placental parts (P = 0.001), placenta expulsion duration (P = 0.002) and time of last placental part expulsion (P = 0.024). If oxytocin was used, number of expelled placental parts was positively associated with number of liveborn piglets (β = 0.2 ± 0.1; P = 0.002) and affected by parity. 5th parity sows expelled more placental parts (4.3 ± 0.4) than 4th (3.2 ± 0.3; P = 0.024) and 3rd parity sows (2.7 ± 0.4; P = 0.008). Furthermore, placenta expulsion duration was positively associated with number of liveborn piglets (β = 18 ± 8 min; P = 0.025). First placental part expulsion was negatively correlated with farrowing duration (β = 0.3 ± 0.1; P = 0.001). Sows that experienced total (no expulsion of placental parts; n = 4) and partial retained placentas (no expulsion of placental parts after birth of the last piglet; n = 4) had longer farrowing durations (1009 ± 275 and 734 ± 136 min) than sows with no retained placentas (369 ± 202 min; P = 0.021 and P = 0.004). The results show that a prolonged parturition impaired and oxytocin improved placenta expulsion in sows. Furthermore, retained placentas occurred in 3-6% of the sows and was correlated with a prolonged parturition.