Sows detected in oestrus between 2 and 6 days afterweaning were homogeneously distributed within threetreatment groups (trios) according to parity (three to six),mean lifetime number of piglets born (9–19 piglets), pre-vious lactation length (18–24 days), number of weanedpiglets (9–14 piglets), and body condition score at insemi-nation on a scale of five points (Young et al., 2004). Selectedsows at oestrous onset had, on average, 4.5 ± 0.04 parities,12.9 ± 0.06 mean lifetime piglets born, 10.7 ± 0.06 weanedpiglets, 22.0 ± 0.06 days of lactation, 4.3 ± 0.02 days ofinterval between weaning and oestrus, and a body condi-tion score of 3.1 ± 0.01 points.