Natural Farrowing Behavior of the Sow and Piglets
To determine the best practices for providing good sow and litter welfare in the farrowing accommodation, a good starting point is to re-examine the behavioral patterns that have been documented around farrowing and during lactation, in a natural or semi-natural environment. There is a series of behaviors carried out, with sows and piglets undergoing various phases of isolation, community integration, and living. Jensen has proposed that maternal behavior can be divided into six distinct parts: (i) isolation and nest site seeking, (ii) nest building, (iii) farrowing, (iv) nest occupation, (v) social integration, and (vi) weaning .
Isolation and Nest-Site Seeking
Outdoor wild, feral, and domestic sows proceed through isolation and nest-site seeking 48 to 24 h prior to the birth of the first piglet. The sow will leave the social group and seek isolation. Sows walk great distances, between 1½ and 4 miles (2.5 and 6.5 km; [2-3]) and investigate many potential nesting sites before finally being chosen. Jensen noted that the sites were often situated away from the usual “home range” of the sow, and were often chosen to provide a degree of both vertical and horizontal protection and some form of a slope [2, 4]. When choosing a suitable nesting site, sows preferred: (1) to use a variety of substrates for nest construction, (2) that the nest walls were structurally sound with well-formed sides, and (3) for the ground to slope .
Nest building behavior involves an organized sequence of activities. The chosen nest-site is hollowed out to a depth of 2 to 4 inches (5 to 10 cm) by rooting . Grasses, roots, and leaves are collected, and are used to line the nest. Larger branches are arranged over the nest, and grass and other fine materials form a roof over the branches. The effort that can be made to construct the nest can perhaps be illustrated by the fact that a single nest of a free-ranging sow in Brazil contained 560 lb (255 kg) of plant material! .
Farrowing often begins a few hours after the end of nest-building. Sows are usually passive once farrowing starts, and carries out very few postural changes. Sows often stand, turn, and sniff the first piglets born ; but this behavior declines as more piglets are farrowed. Sows do not get up to help the piglets from their membranes. The umbilical cord is normally torn when the piglet moves around to the udder. Jensen proposes that this passivity may be due to the fact that the sow gives birth to a large number of active young, and that to engage in maternal behavior individually as the piglets are born, may place them at unnecessary risk of accidental crushing. After farrowing is complete, sows are inactive for 90 to 95 % of the time during the first 48 hours. This inactivity may be a behavioral adaptation by the sow to reduce crushing, and to allow the establishment of a teat order .
Nest occupation occurs over the 7 to 10 days after farrowing is complete. Maternal behavior has a very organized pattern mainly revolving around nursing. Nursing can be initiated either by the sow lying on her side and presenting her teats, or by the piglets squeaking at her head and (or) massaging the teat area. Eventually the whole litter vigorously butts and jostles for position at the teats, with or without attaching themselves . Often at this time, piglets vocalize intensely and continually . Götz reported that sows spent most of their time in farrowing stalls in lateral recumbency (62 to 85 %); but this decreased over the lactation period . Ellendorff and Poulain reported that during nursing, the sow’s grunts became rhythmical and grunts were low at first but became more rapid . While rapid grunting was still in progress, the whole litter became quiet, with each piglet suckling. This period lasted between 7 to 38 seconds (average 15 seconds), and was followed by another phase of active stimulation with predominant piglet behaviors involving butting and nosing at the udder. This later period ranged from less than 1 minute up to several minutes, until piglets either detached themselves from the teat, fell asleep, engaged in other activities, or the sow ended the nursing period by standing up or rolling onto her sternum to hide her teats .
In a free-range situation, the sow and piglets stay away from the rest of the herd for at least the first week after birth . During the first 1 to 2 days, the sow eats very little, and stays close to her nest . Later, she leaves the nest for longer periods, eats further away, and eventually rejoins the herd for morning feeding (on average 7 days after birth). The litter remains in the nest for a further 2 to 3 days, until the nest is eventually abandoned and the litter is gradually introduced into the herd. The behavior of the sow and litter during this stage of nest occupation probably establishes the sowoffspring recognition that is important once social integration has occurred . Social integration for the sow and her litter occurs gradually over the next few days. Free-range sows begin integrating their litter into the herd towards the end of the second week . This allows time for family bonding to become complete before introduction to other litters. This introduction results in a shift of social interactions away from litter-mates towards other piglets of a similar age . The frequency of these interactions gradually decreases to a steady low level after about eight weeks. These results have important consequences for the design of group farrowing accommodation. It would seem to be appropriate to allow mixing of litters prior to weaning, but not before about 14 days postpartum [13, 14].
Weaning is likewise a gradual event, in effect, natural weaning starts early in lactation. The frequency of suckling declines gradually from the first week, and the number of suckling terminated by the sow increases, perhaps indicating that the sows become less inclined to nurse . Piglets begin to consume solid food from around 4 weeks postpartum. By 8 weeks, solid food constitutes a large part of the piglets’ diet [15-16]. The number of piglets missing from suckling also gradually increases. Weaning is completed anywhere between 8 weeks  and 19 weeks postpartum . There can be a quite large variation in weaning age occurring within a given litter .
Understanding how the sow’s behavior alters before, during, and after farrowing can help scientists and producers incorporate unique facility designs into the farrowing environment. Single or additive alterations to the environment may enhance the welfare of the sow and her litter. For example, encouraging the sow to remain passive during the first 72 hours after birth reduces the risk of piglets being killed through over lay by the sow. Finally, good and consistent sow performance likely will improve her productive lifetime within the herd.
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