Effects of parity, season and boar contact on the reproductive performance of weaned sows

Forty eight Large White x Landrace sows(12 from parity 1, 12 from parity 2 and 24 from parities 3-7) were allocated to each of 4 post-weaning boar contact treatments (0, 1, 2 or 3 exposures day(-1)) in each of the four seasons of the year. Litter size suckled was standardized at 10 piglets wherever possible (range 9-12 piglets) and lactation length was 24-35 days. Oestrus detection was performed twice-daily on all weaned sows and each sow was given 2 fertile matings 24 h apart. Data on anoestrus, conception rate and subsequent litter size were also collected. Sows being weaned from their first litter took significantly longer to return to oestrus post-weaning than did sows in parities 2-7 (5.9 +/- 0.38 vs. 5.1 +/- 0.21 days, P < 0.05). There was no significant influence of boar contact post-weaning on the length of the rebreeding interval (5.5, 5.5, 5.4 and 4.9 days for sows receiving boar contact 0, 1, 2, or 3 times daily respectively). Equally, season of the year did not significantly influence the length of the rebreeding interval (5.1, 5.2, 5.3 and 5.6 days for sows being weaned in spring, summer, autumn and winter respectively). The size of the litter subsequently produced was significantly influenced by sow parity (12.1 +/- 0.46 vs. 13.1 +/- 0.28 piglets born to sows having either their second or third-eighth litter respectively) but was not significantly affected by either boar contact in the post-weaning period or season of the year. Subsequent litter size was also significantly affected by the litter size of the sow at the start of the experiment (r = 0.40, P < 0.001), These results suggest that, with the exception of parity-1 sows, extended weaning-to-oestrus intervals are not a major problem in some sow genotypes. Furthermore, where the weaning-to-oestrus interval is extended, these results indicate that the provision of regular boar contact post-weaning is unlikely to stimulate an earlier return to oestrus, (C) 1998 Elsevier Science B.V. All rights reserved.