General recommendations are made (e.g. Gomes, 1977; Dzuik, 1970) that, in order to achieve maximum conception rate and litter size, sows should be mated or inseminated 9 to 15 hours prior to ovulation and that this coincides with an interval of 30 to 36 hours after the start of standing oestrus (SO). This assumes that sows will be in standing oestrus for around 48 hours. Surprisingly little data is available on the length of SO In modern sows on current production systems. Accordingly length of SO was determined in a large commercial herd weaning at around 3 weeks of age.
A team of observers determined the start, completion and duration of SO in 101 multi parity sows. The sows were tested for SO daily from weaning at 8 hourly intervals (00.00, 08.00 and 16.00 hr) until the end of SO by taking sows individually from their small post-weaning groups to an oestrus checking area. Boars were penned around this area and SO was checked using the back pressure test.