Post-partum oestrous behaviour in sows is not associated with ovulation

Sows occasionally show oestrous behaviour within 5 days of farrowing; this is termed post-partum oestrus (PPO). This study investigated the incidence and possible causes of PPO on nine Dutch farms. Lactation records (n=1374) were used, backfat thickness was measured (n=25), and ovarian condition was assessed by transrectal ultrasonography. The incidence of' PPO ranged from 0% to 62% on the different farms. On average, PPO started 59 hours after farrowing and lasted for 55 hours. Sows with PPO were younger than sows without PPO (parity 3.8 +/- 0.2 vs 4.4 +/- 0.1, respectively; P < 0. 05) and had more backfat than sows without PPO (21.3 +/- 1.2 vs 17.9 +/- 1.2 mm, respectively; P < 0.10). Occasionally, some follicle growth was observed in sows with PPO, but ovulation did not occur. PPO did not affect the weaning-to-mating interval or piglet mortality during lactation.