4. Discussion
Studies by Haskell and Hutson (1996) and Damm et al. (2003) showed that sows perform increased activity behaviour in terms of postural changes during the pre-farrowing period in different kinds of housing. In the present study, sows housed in crates, particularly primiparous NC-sows, performed an activity expressed in increased standing behaviour and decreased descending from standing to lying prepartum. Jensen (1989) observed in loose-housed sows a peak of activity in the period 16–8 h of pre-farrowing, especially standing, in which nesting behaviour typically occurred. At this time peak, the behaviour of crated NC-sows and C-sows differed significantly in the present study, as well. Especially primiparous NC-sows stood more often than primiparous C-sows. Additionally, in this activity NC-sows performed significantly more often and in longer bouts nest-building behaviour pattern equal to their wild ancestors, even in crates without any available nest-building material. The onset and performance of nest-building is both stimulated internally via hormones, for instance prolactin, and externally via feedback from the environment. With this environmental influence, the possibilities to perform nest-building can be restricted to different extents in commercially farmed pigs, but elements of this innate behaviour are always shown (Wischner et al., 2009). Due to the lack of material, nest-building behaviour was performed only against the floor and fittings of their crates. Damm et al. (2003) assessed that the crate environment restricted the sows either indirectly due to a feedback mechanism or directly by preventing physical activity, so that more fragmented nest-building behaviour was observed in crates than in pens. However, in this study, sows in crates did perform nest-building behaviour, and differences between NC-sows and C-sows were identified additionally. NC-sows performed longer nest-building behaviour more often. In another study, non-crusher sows showed significantly more nest-building activities before the onset of farrowing than crushers (Andersen et al., 2005). However, Pedersen et al. (2006) described that the passivity of sows, represented by low nest-building activity, was followed by low postpartum motivation for behavioural patterns and resulted therefore in safer postural changes for the piglets. Even though comparison between different studies is limited because of differences in the observed parameters and housing conditions, these results could not be confirmed in this study. Lower nest-building activity as shown in C-sows, was followed by higher piglet mortality.
The reasons for crushing are difficult to analyse, since behaviour patterns which sows and piglets perform to avoid crushing need to be considered not only in their occurrence, but also in the way they are performed (Pedersen et al., 2006). In this respect, the motivation for ‘careful’ behaviour has to be regarded. In this study, further detailed observations to possible piglet responses associated with vocalisation from the dam could not be determined, because there was no audio information on the time-lapsed video records.
Another cause for crushing is related to litter size. Johnson et al. (2007) showed that crusher sows had more piglets born per litter than non-crusher sows. One biological reason for fatal trampling and crushing may be that it represents an alternative way of reducing maternal investment, especially in large litters (Andersen et al., 2005). In a similar way, the Parental Investment Theory (Evans, 1990) claims that any parental investment in the offspring lowers the parent's ability to invest in future piglets, and is therefore decreased with higher parities (Held et al., 2006).
However, in larger litters, piglets’ body weights vary, and therefore, the risk of crushing is increased for the smaller ones. On the contrary, breeds with large litters, for instance Meishan sows, show lower losses due to crushing, because they are more vigilant and aware of the piglets’ location (Hohenshell et al., 1996).
Our results showed that C-sows preferred the ventral recumbency for a longer duration and as final position of descending from standing to lying. This lying position does not allow the piglets’ full access to teats, as in lateral recumbency (Damm et al., 2000). Therefore it has been reported that optimum maternal behaviour is characterised by passivity and lateral lying (Jarvis et al., 1999 and Hellbrügge et al., 2008b). Thodberg et al. (1999) found that after the initial, more active period, sows generally lie in lateral recumbency. Cronin and Smith (1992) observed a longer duration of lying in lateral recumbency from 65 to 95% of total time the first day after farrowing. In our study, NC-sows performed in the first day after parturition significant longer bouts of lateral recumbency, which permitted the piglets to find and remain near the udder to consume colostrum.
The manner of descending from standing to lying had an essential influence on the crushing risk in piglets (Vieuille et al., 2003). In the present study, only the final lying position after descending from standing to lying differed between the NC-sows and C-sows. C-sows preferred more often ventral recumbency after sitting and kneeling on the front of legs, while NC-sows preferred lateral recumbency after sitting and kneeling on front of legs. Consistent with Marchant et al. (2001), no association was detected between times taken to lie down and crushing. However, Damm et al. (2005) described the risk of crushing to be highest during fast and uncontrolled body descending, because piglets had less time to escape or to vocalise loudly. In agreement with this statement, in our study 70% of the piglets were crushed while the sow performed descending from standing to lying. The manners in which the sow lay down were not relevant for the piglets’ deaths due to crushing by the sow.
Generally, the risk of crushed piglets rises when the piglets have consumed little or no colostrum, especially when the sow performs many postural changes (Weary et al., 1996b). In particular, rolling behaviour was shown more often and in longer bouts by primiparous C-sows in comparison with primiparous NC-sows. In our study, 22% of all crushed piglets were related to rolling behaviour. C-sows swapped sides from lateral or ventral recumbency to ventral recumbency more often than NC-sows. But in opposition to Damm et al. (2005), slower rolling movements of primiparous C-sows were identified as risky behaviour. In the contrary, in multiparous NC-sows, slower rolling movements decreased the risk for the piglets. This is incompatible with Svendsen et al. (1986), showing an increase of the crushing risk for sows in higher parities. This is most probably related to the gain in body size, resulting in a reduced agility and phlegmatic behaviour in general (Weary et al., 1998). The effects of the confinement by crates become more apparent in heavier multiparous sows that are slowed down in their rolling movements. On the contrary, primiparous sows are still able to perform rolling movements in a different manner and frequency due to their smaller size.
Usually, sitting was an unavoidable stage during postural change from lying to standing whereas it was not necessary vice-versa from standing to lying. C-sows performed a significant higher sitting duration than NC-sows after parturition. After farrowing, sows in a sitting posture could not stay close to their piglets. But this proximity is necessary to provide warmth and access to the udder to obtain adequate milk intake (Weary et al., 1996a). The most dangerous body movements for the piglets occurred when the sow lay down in an uncontrolled manner, even from sitting to lying (Edwards et al., 1986). In the present study, only 11% of piglets were crushed by descending from standing to lying, starting with a sitting position. By descending from standing to lying, 63% of the piglets were crushed. Despite this high percentage, no differences between NC-sows and C-sows in their descending from standing to lying performance were observed. This might indicate the involvement of traits that were not assessed in our study, for instance a better responsiveness to their piglets or a different vocalisation in NC-sows.
5. Conclusion
A better understanding of behavioural patterns in farrowing behaviour is essential for increasing the proportion of piglets weaned and thus improving economic success in pig production. A significantly longer duration and higher frequency of standing posture, and a significant higher frequency in standing-up and lying-down combinations was performed by NC-sows in our study. This higher activity in NC-sows might express a better responsiveness towards their piglets. Further research with comprehensive sampling should concentrate on traits with significant differences which have to be verified, indicating a possible use in selection of sows with optimal maternal abilities.