Group-housing of lactating sows: effects on sow health, reproduction and litter performance

Group-housing systems for lactating sows have been developed and tested since the mid-1960's, the goal being the increase productivity and improve welfare. The group-housing system most commonly used in Sweden in characterised by individual farrowing and group-housing from about two weeks after parturition until weaning. The aim of the present work was to evaluate this system from health and performance perspectives under commercial conditions. Data collected from four commercial farms using the group-housing system was compared with corresponding data obtained from three farms on which sows were kept individually penned throughout lactation. To evaluate ovarian activity during lactation a faecal progesterone/progesterone metabolite ('progestin') assay was developed and validated. No major difference was found between the two housing systems in terms of sow health status at the time of weaning. However, teat and udder-skin wounds occurred less commonly among the multiparous group-housed sows than among the multiparous conventionally housed sows. Group-housed sows seemed to have a thicker backfat layer at the time of weaning and consumed 23% more feed compared with individually housed sows. The faecal 'progestin' assay showed good biological and methodological validity. HPLC-separation of a luteal phase faecal sample indicated that pure progesterone is partly responsible for the immunoreactivity in the assay. Ovulations during lactation occurred in 28% of the group-housed sows. A positive relationship beteen the occurrence of oestrus and sow age was revealed. Some sows that ovulated during lactation weaned their litters before the set time of weaning. Only 1% of the individually housed sows ovulated during lactation. There were no significant differences in piglet weight or growth rate between the two housing systems during the group-housing or post-weaning period. Variation between herds within housing system was large. During the group-housing period piglet mortality was significantly higher among the multiparous group-housed sows' piglets than among piglets of the individually housed multiparous sows. Variation between batches within herd was large. Among multiparous sows, the percentage of sows mated within 10 days post-weaning was significantly lower in the group-housing system than in the individual housing system. Repeat breeder frequency was also higher among the multiparous group-housed sows, compared with the individually housed multiparous sows. Repeat breeding/failure to farrow was a common reason for culling in the group-housing system.