NADIS BPEX Commentary – February 2011

UK - Preweaning or piglet mortality is one of the most readily recorded parameters of pig productivity and within the breeding herd it represents a very sensitive measure of change, according to BPEX's monthly NADIS commentary for February 2011.
calendar icon 3 March 2011
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Within a rigid batch system, the preweaning mortality can be expressed as a percentage of the total number of pigs born alive within that batch and as such can only be obtained once the batch reaches the end of that recording period i.e. weaning. For this reason, it is more common, in order to keep a close watch on events within the farrowing area, to express preweaning mortality as the number of pigs dying between birth and weaning within a given time period, as a percentage of the number of pigs born alive within that same time period. However this does mean that due to erratic birth numbers as well as variations in deaths, the recorded mortality percentage can fluctuate widely.

The NADIS surveillance system therefore aims to smooth out such fluctuation by collecting preweaning mortality data over a three month period and the figures then submitted each month are expressed as a three monthly average. Graph 1, measuring nearly four years of data within the surveyed population shows a gently undulating picture with very broadly a lower mortality in summer months and higher in the spring. Because reporters are collecting data in retrospect, covering the three months farm mortality preceding the quarterly visit, this actually means that the lowest levels of preweaning mortality tend to occur in the spring and the higher levels in late summer and winter.

The general picture of mortality between herd types is:-

  1. Graph 2 – mortality tends to reduce as herd size increases possibly implicating more specialised stockmanship and better cross-fostering ability
  1. Graph 3 – breeder weaner herds, within the surveyed population, have the lowest mortality. Care is needed here regarding the breeding only herds which are very high.

The figures may be confounded by the outdoor effect – see below.

  1. Graph 4 (above) – Mortality outdoors is noticeably higher than indoors and pigs farrowing on slats have a lower mortality compared to those on straw. Perhaps surprisingly there is very little difference between the batch and continuous flow system with respect to preweaning mortality.
  1. Graph 5 – regional variation is very marked with East Anglia recording piglet mortality 30 per cent higher than NE England. This may again reflect the outdoor effect.

Perhaps the most revealing data relates to the pattern of death through 2010 between the indoor and outdoor sectors (Graph 4a). Indoor, three months rolling average mortality has consistently recorded between 11 and 12 per cent of pigs born alive. Not only are the figures higher outdoors but the variations are very marked. A dramatic rise in outdoor mortality is seen in the January/February/March – March/April/May period. Due to recording lag and the effects of rolling averages this actually equates to a steep rise in mortality outdoors at the turn of the year and into February, i.e. it corresponds with the severe weather problems experienced through Jan 2010. Mortality then falls, although there is surprisingly an uplift in June/July/August representing here a spring/early summer increase. The lowest levels recorded are September/October/November representing the later summer farrowing period.

Finally the curve turns up again in October/November/December representing the weather deterioration from late November onwards. It would be expected that, if this pattern is purely weather related, the outdoor graph will continue to climb over the next 3x3 month blocks to reflect the severe problems of cold and snow in December and January.

Interestingly this dramatic pattern outdoors in 2010 was not seen in 2009 within the surveyed population (Graph 4b).

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