Influence of different sow traits on the expulsion and characteristics of the placenta in a free farrowing system.

The last phase of parturition is the detachment and expulsion of the placentas and should not exceed a duration of 4 h after the birth of the last piglet. At present, only a small amount of information is available about factors influencing the expulsion of the placenta, especially in sows accommodated in free farrowing systems. This study aimed at investigating the influence of sow traits on placenta expulsion in a free farrowing system in Switzerland. In this study, 48 crossbred sows were included and the following traits of the sows were investigated: Backfat thickness, birth induction with at least 116 days of gestation with prostaglandin F2α, placenta parts and weight, placental efficiency (quotient of litter weight and placental weight) and expulsion of the first placenta part in relation to the last piglet. In addition, the farrowing process and litter parameters were recorded. The piglet expulsion duration (260.3 ± 199.5 min) and placenta expulsion duration (388.7 ± 300.2 min) were positively correlated (p = 0.001). Sows that expelled the first placenta part simultaneously with the last piglet or even before the last piglet was born showed a significantly prolonged piglet expulsion duration in comparison to sows that expelled the first placenta part after the last piglet was born (305 ± 216 min vs. 139.0 ± 34.9 min; p < 0.01). Sows with 2-4 placenta parts had a significantly shorter farrowing (292.91 ± 117.92 min) and placenta expulsion duration (160.73 ± 104.00 min) than sows with 5-7 placenta parts (634.63 ± 330.79 min farrowing duration; 460.77 ± 337.32 min placenta expulsion duration) and sows with 8-10 placenta parts (599.00 ± 138.20 min farrowing duration; 438.43 ± 117.98 min placenta expulsion duration) (p < 0.01). Sows with placental efficiency <5 were characterized by a significantly higher number of liveborn piglets compared to sows with a placental efficiency ≥5 (17.1 ± 2.7 piglets vs. 13.6 ± 2.8 piglets; p = 0.002). This is the first study that evaluated the placental characteristics in a free farrowing system and compared it with specific sow traits. Especially, the expulsion of the first placenta and the number of placenta parts could be a reliable parameter to detect sows with obstetric problems and therefore enable improvement sow and piglet health.