The causes and timing of piglet mortality were studied in different farrowing systems. In the first experiment 198 litters were recorded in three systems, two of which allowed the sows to move freely, and the third restricted them in conventional crates. More piglets were weaned from the conventional crates than from the open systems and they grew more quickly. More than half the liveborn mortality occurred during the first four days after parturition. In the open systems, 17 per cent and 14 per cent of the piglets born alive were crushed, compared with only 8 per cent in the crates. In the second experiment, 29 sows and litters were studied in detail in a communal pen system during the first seven days of lactation. Three-quarters of the liveborn mortality was due to crushing. The total number of piglets dying per litter, including stillbirths, was significantly associated with the total litter size and the sow's parity. The percentage liveborn mortality was significantly associated with the parity and body length of the sows and with the within-litter variation in the birth weight of the piglets. Individual birth weight was closely associated with percentage survival. Only 28 per cent of piglets weighing less than 1.1 kg at birth survived to seven days.

The objectives of this study were to establish what changes in posture by sows carried a high risk of piglet crushing in a group farrowing system during early lactation and also to determine what factors influenced the risk of crushing during lying down. A total of 24 Large White ✕ Landrace sows were studied during the first 7 days of lactation in a group farrowing system. Cross-fostering was not carried out so as not to influence behaviour. Dead piglets were removed and cause of death ascertained from external observation and post-mortem examination. Sow and piglet behaviour was video-recorded continuously. A total of 268 piglets were born alive, with 67 liveborn piglets subsequently dying during the 7-day experimental period, 50 as a result of crushing. A total of 7425 posture changes were analysed and 11 types of posture change were identified, the most dangerous being lying down from standing and those involving swapping sides, or rolling over, whilst lying.Dangerous events during lying down were more likely to occur (1) in the first 24 h after farrowing, (2) when the sow lay down in the middle of the pen, (3) when the sow lay down without carrying out much piglet-directed pre-lying behaviour and (4) when the piglets were spread out but near to the sow. The amount of pre-lying behaviour decreased over time and crushing mortality also decreased. The results confirm that the piglets are most vulnerable to crushing during the first 24 h of life, when they are spending much of their time near the udder and have relatively poor mobility. Co-ordination of behaviour between the sow and her litter is important to reduce the risk of crushing. It is also important that the design of open farrowing systems incorporates knowledge about how crushing deaths occur in order to improve piglet welfare.

Compared with small groups, housing in large groups offers the pig more total available space, resulting potentially in an increased degree of control over its (micro) environment. For the producer, large groups require fewer pen divisions and offer more possibilities for the sharing of resources such as feeders and drinkers. However, whilst large groups may offer benefits to higher ranking animals in the group, there may be serious disadvantages for those further down the social hierarchy, who also need to compete for access to resources. This study investigated the interactive effects on welfare of food availability (one single space hopper per 20 or per 10 pigs) and group size (20, 40 or 80 pigs per pen), at constant stocking density (0·55 m2per pig) in part-slatted pens. Groups provided with two feeding spaces per 20 pigs were less active than groups with one feeding space per 20 pigs. The number of aggressive interactions per pig at the food trough was not affected by group size but decreased with number of feeder spaces per 20 pigs. The number of skin lesions increased with group size. Average daily gain in the first half of the finishing period was negatively influenced by group size and positively by number of feeding spaces. No effect on weight gain was found subsequently. Within-group variation in growth was not affected by group size or number of feeder spaces. No differences between treatments were found in the number of pigs removed for health reasons. Interactive effects of the two treatments were found on some behaviours but not on any of the performance variables measured. It is concluded that, from a welfare point of view, the number of pigs per feeder space should be lower than 20, although performance levels appear acceptable at 20 pigs per feeder. Further research will have to identify whether the effects of group size on general aggression is common to all finishing pig systems, or whether the presence of straw can serve as a mitigating factor.

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