The Thai Journal of Veterinary Medicine


The aim of the present study was to investigate the effects of the weaning-to-oestrus interval (WOI) and parity on the expression of oestrus and the timing of ovulation in crossbred (Large White x Landrace) sows. The detection of pro-oestrus and oestrus was performed every 8 hrs in all sows, by observing the reddening and swelling of the vulva and by applying the back pressure test in the presence of a boar. Ovulation was monitored every 8 hrs using transrectal ultrasonography. The duration of oestrus was 59.1, 59.8 and 65.3 hrs for parities 1, 2 and 3-4, respectively. Parity 1 and 2 sows had a significantly shorter oestrus duration compared with parities 3-4 (p<0.01 and p<0.05, respectively). No difference in the pro-oestrus duration and ovulation times were found among parity 1, 2 and 3-4 sows. No difference in the pro-oestrus duration was found among sows with a WOI of 1-3, 4 and 5-7 days. Oestrus duration from the onset of standing oestrus to ovulation was 67.4, 58.5, 58.2 hrs and 48.6, 41.5, 40.2 hrs for sows with a WOI of 1-3, 4 and 5-7 days. Sows with a WOI of 1-3 days had a significantly longer oestrus duration and a longer ovulation time than sows with a WOI 4 and 5-7 days (p<0.001 and p<0.05, respectively). A significant negative correlation between the WOI and oestrus duration (r=-0.30, p<0.001) and between the WOI and ovulation time (r=-0.33, p<0.001) was observed. Oestrus duration was positively correlated with the ovulation time (r=0.82, p<0.001), but was negatively correlated with the relative ovulation time (r=-0.23, p<0.01). It was possible to use the WOI and the oestrus duration to predict the ovulation time.

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