Ovarian activity and oestrous signs among group-housed, lactating sows: influence of behaviour, environment and production.

Animal welfare concerns require the development of housing systems that allow the animals to express their natural behaviour. One example of this is the group-housing system for lactating sows. The present study aimed at exploring ovarian activity in such a system. Thirty-eight sows farrowing individually outdoors during spring and summer, and indoors during autumn and winter, and group-housed in groups of four during weeks 3-7 of the lactation period, were monitored regarding reproductive functions, behaviour and production during their first to fourth lactation period. Average ovulation frequency during lactation was 47%. Only 50% of these ovulating cases were accompanied by a standing oestrus. Lactational ovulation frequency was higher in later parities (p < 0.001). Ovulation frequency was higher (p < 0.05) during winter (74%) and spring (69%), than during summer (10%) and autumn (23%). Occurrence of lactational ovulation was associated with some aspects of suckling behaviour and also with litter weight gain (p < 0.05). Forty-nine per cent of the lactational ovulations occurred during the seventh week of lactation. Timing of ovulation seemed positively (p = 0.08) associated with weight loss during lactation. Compared with the sows that were anoestrus during lactation, oestradiol-17beta values were higher (p < 0.05) only in the week before occurrence of lactational ovulation. Weaning-to-oestrous interval was prolonged (p < 0.05) among the sows that ovulated during lactation. The present study identifies several factors influencing ovarian activity among group-housed sows, thereby providing tools for the control of lactational ovulation in group-housing systems.