Cross-suckling when sows are group housed during lactation : associations with sow productivity and behaviour

Abstract: Cross-suckling, i.e. when an offspring nurses a female other than their own mother, occurs in pig production systems where sows are group housed during lactation. As production systems where several sows and their litters are housed together during lactation are getting more common, the need of knowledge regarding cross-suckling increases. The overall aims with this thesis was to investigate how sow behaviour and productivity are associated with the occurrence of cross-suckling, and to investigate consistency in sow nursing behaviour related to cross-suckling. The study included information about the first 4 parities of 40 LxY sows kept in outdoor and indoor production environments. Sows were single housed the first 2 weeks after farrowing and group housed (4 or 5 sows per group) from 2 weeks after farrowing until weaning, 7 weeks after farrowing. Cross-suckling, nursing behaviour and sow time budgets were registered during 6 hours of continuous direct observation one day week 4 and one day week 6 after farrowing. Sow weight and back fat depth were recorded at farrowing, 2 weeks after farrowing and at weaning. Piglets were weighed at day 4 post partum (pp), day 14 pp and at weaning. The results showed that sows that allowed cross-suckling week 4 lost on average less back fat between week 2 and 7 pp (p = 0.002). The trend was the same for week 6 (not significant). Sows that allowed cross-suckling had smaller litters (week 4: p = 0.012; week 6: p = 0.029). Sows willingness to allow cross-suckling is repeatable within lactation (between week 4 and week 6: r = 0.36, p <0.001) but not over lactation. In conclusion, cross-suckling is not a long term individual trait of the sow; it is affected by the environment and by body condition. Sows with smaller litters were more prone to allow cross-suckling.