Some mortality in sows is inevitable during production and, nowadays, sows euthanased on farms due to injury or disease rendering them unfit to transport for slaughter or for presention for human consumption, contribute a significant proportion of the losses on some farms.

Over the last few years the mortality rate in sows within the surveyed population has varied between the range of 4-6 per cent annualised (with a very brief dip below 4 per cent in late 2007) (Graph 1).

Over the last twelve months, sow mortality has risen above levels seen in previous years and has been somewhat variable. In 2009 mortality started to rise from its baseline of 4 per cent peaking at more than 5 per cent in the summer. Until very recently 2010 figures have been consistently above 5 per cent and touching 6 per cent in early summer. The 2009 figures are broadly consistent with that quoted for an unspecified national population (BPEX yearbook 2010) of 4 per cent.

Within the NADIS population, the lowest mortality rates are seen in the smaller herds with the peak seen in herds of 5-700 sows (Graph 2). The largest herds are slightly lower than this, but may be distorted by the small number of herds involved and the fact that there is a big difference in recorded mortality of sows between indoor and outdoor farms and there is a tendency for outdoor herds to be larger (see below).

There is no discernable pattern or trend in sow mortality between different herd types (Graph 3) but management systems can have a major influence on losses (Graph 4).

Death rates in sows in outdoor farms are reported to be at 50 per cent of the level of that seen indoors (2.5 per cent v 5 per cent) suggesting that adverse weather conditions (severe cold, wet conditions, etc.) are offset by space and exercise available to outdoor sows.

There is a small numerical difference in favour of slatted housing systems when measuring sow mortality but is of very dubious significance. It does however suggest that the potential for injury to sows on slats often claimed is not manifest in this population as higher death rates. There is no material difference in sow mortality between batch and continuous flow systems.

Highest regional mortality is reported in Northern England where indoor herds predominate (Graph 5). Space provision for sows has been highlighted as a key factor in bullying and injury to sows on some farms by NADIS reporters.

There is a perception that high sow mortality is a direct consequence of high productivity – sow deaths in the prolific Danish herds are reported at 14.4 per cent although only 5 per cent in the similarly producing Dutch herds (BPEX 2009 Pig Cost of Production in Selected Countries). Within the NADIS population whilst the lowest sow mortality is seen in the poorest producing herds, there does not appear to be a rising penalty as herd output increases above 22p/s/y, and it cannot be concluded from this data that higher levels of productivity are consistent with higher mortality (Graph 6).