Relationship between farrowing and piglet traits, and mortality in a free-farrowing system

Free farrowing systems have been related with increased piglet mortality in case of large litter size. On the other hand, public concern about animal welfare is guiding pig industry towards production with free farrowing pens. Aim of the study was to identify the relationship between piglet mortality during the first 24h after start of farrowing in a free farrowing system and farrowing and piglet traits. The births of 259 piglets [Duroc × (Danish Yorkshire × Danish Landrace)] from 15 sows were video recorded. The sows were kept in free farrowing pens (crate size: 220 × 80 × 180 cm, pen size: 250 × 240 cm). At birth, body weight of each piglet was recorded by sampler. The birth order, birth interval, vitality score and latency from birth to first udder touch (latency to udder) of each piglet were determined from the recording. The average number of live-born piglets per litter was 17.3 ± 2.7 and total live-born mortality was 17.3%. Forty five piglets died, of which 39 were crushed and 6 died due to other causes. There were no significant differences between piglets that died or survived in their birth interval, cumulative farrowing duration or vitality score. However, died piglets were tended to have earlier relative birth order than survived piglets (42.9 ± 4.9 vs. 51.4 ± 2.1 %; P = 0.073). In addition, piglets that died had lower birthweight (1088.5 ± 60.1 vs. 1315.2 ± 23.7 g; P < 0.001) and longer latency to udder (52.3 ± 10.7 vs. 34.4 ± 2.9 min; P = 0.033) compared to piglets that survived. Our study suggests that low birthweight and long latency to udder, which might affect colostrum intake and increase risk for hypothermia and therefore may lead to crushing, were the major causes of piglet mortality in free farrowing system with large litter size