Incidences of retained placenta and their effect on subsequent fertility in sows

Increased birth duration, possibly due to secondary uterine inertia, is known to decrease subsequent fertility. The aim was to investigate the expulsion time of placenta and retained placenta. At birth, we recorded 149 sows for the following farrowing traits: time interval between birth of first and last piglet (mean SD, 411 250 min, BD), time interval between expulsion of first and last placenta (273 223 min, PlD), time between expulsion of last placenta relative to the last piglet (263 221, LPLPD), and primary placental retention without expulsion of placenta (PPR). For relations between BD and PlD and LPLPD, a linear regression model was used including parity and litter size as explanatory variables. For relations between BD and PPR, a logistic regression model was used. With increasing BD, PlD increased (p = 0.086) and LPLPD decreased (p = 0.003). In 55% of the sows LPLPD was <4 h, in 39% 4–12 h, and in 6% >12 h (secondary retained placenta). There was a relationship between BD and PPR (p = 0.001). In 3% of the sows (n = 4), no placenta was expelled after the last piglet (BD 660 177 min) and in another 3% no placenta was expelled at all (n = 5, BD 1008 275 min), whereas BD was 386 226 min for the remaining animals. Sows with PPR were given a PlD value of 0 min and a logistic regression model was used for effects of PlD and LPLPD on the subsequent pregnancy rate (PREG vs. NotPREG, n = 125 PREG, 17 NotPREG, 7 animal without status). PlD was 272 233 min (PREG) vs. 153 178 min (NotPREG, p = 0.031). LPLPD was 268 228 min (PREG) vs. 169 172 min (NotPREG, p = 0.061). The results show that retained placenta occurs frequently. Secondary retained placenta seems not to be related with subsequent fertility, whereas primary retained placenta obviously does so.