Studies in sow reproduction 6. The effect of lactation length on pre-implantation losses

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Abstract
Thirty Landrace × (Landrace × Large White) sows were used to investigate the importance of pre-implantation losses in the embryonic mortality of the early-weaned sow. The sows were allocated at random to one of two lactation lengths, namely, 7 or 42 days. Following weaning and remating the sows were slaughtered at 9 days post coitum. Ovulation rates were similar for both groups (15·3 and 15·1 for the 7-day and 42-day weaned groups respectively). Numbers of embryos present at 9 days post coitum were 12·5 for the 42-day group and 11·2 for the 7-day group and the difference was non-significant. Percentage embryo survival was 83·5% for the 42-day group and 74·3% for the 7-day group; the difference was non-significant. It was concluded that the bulk of embryo loss in the early-weaned sow occurred after the pre-implantation stage and was probably at or around implantation.