Knox, R. V.; Rodriguez Zas, S.L. Factors influencing oestrus and ovulation in weaned sows as determined by transrectal ultrasound. Journal of animal Science (2001) 79 (12) 2957-2963 Savoy, USA; American Society of Animal Science [ En, 25 ref.] Department of Animal Sciences, University of Illinois, Urbana, IL 61801, USA. Email: [email protected]
Characterization of factors influencing oestrus and ovulation in sows may facilitate development of procedures for improving reproductive performance. The experiment was conducted in confinement during 1997-99 using 174 Large White x Landrace sows. After weaning, sows were checked for oestrus twice daily. In the 1st year, transrectal ultrasound was performed once daily and in the 2nd year, twice daily, at oestrus and every day until ovulation. The effects of lactation length (£ 16, 17-24, 25-31 or ³ 32 d), parity (1, 2, or ³ 3), season (winter, spring, summer, or fall) and weaning – to oestrus interval (3, 4, 5, or 6 to 8 d), including their interactions on oestrual and ovulatory responses, were studied. There was no effect of frequency of ultrasound on any response variable, so data across years were pooled. Percentage of sows expressing oestrus within 8 d of weaning was influenced by lactation length ( P< 0.001) , with sows lactating £ 16 d (35.2%) being less likely to express oestrus than sows lactating ³ 17 d (94%). A parity x season interaction was observed (P< 0.001), for oestrus, with the lowest expression in parity 1 (73.0%) and parity 2 (67.2%) sows during autumn, compared with ³ parity 3 sows (98.1%). No explanatory variable had a significant effect on weaning-to-oestrus interval (4.4 d) or on follicle size at oestrus (8.1 mm). Ovulation hour, after onset of oestrus, was affected by weaning-to-oestrus interval (P< 0.01), with sows returning in 3 d ovulating at 46.2 h and between 6 and 8 d at 30.2 h. For sows that expressed oestrus within 8 days of weaning, the percentage of sows ovulating was influenced by lactation length (P<0.001) and weaning to oestrus interval. Sows that lactated £ 16 d were less likely to ovulate (78.0%) than those lactating ³ 17 d (>92%). Sows that returned to oestrus in 3 d were also less likely to ovulate (79.5%) than sows returning ³ 4 d after weaning (>92%). A parity x season interaction was also observed on ovulation (P< 0.001), with parity 1 and 2 sows less likely to ovulate after expressing oestrus in autumn and spring, compared with parity 3 and greater sows. The data suggest lactation length, early return to oestrus and parity by season effects are associated with risk of failure to express oestrus and ovulate. Copyright CABI Publishing
