NADIS BPEX Commentary – October 2008

Veterinary surgeons undertaking clinical visits to pig farms record the prevalence of a range of syndromes and conditions seen and these are reported through the NADIS system.

With background data on the farms such as farm type, location, size and management systems also recorded, it is possible to make associations between these various parameters and disease conditions.

One such aspect of the growing herd that is recorded is abhorrent (or aberrant) behaviour, colloquially termed vice.

Figures collated over the last 12 months reveal widespread incidence of such behaviour with over 50% of finishing pig holdings recorded at least one occurrence in the year. Tail biting is particularly prevalent, seen on 40% of all holdings, whilst flank and ear biting (differentiated from ear tip necrosis) have occurred in 13% of farms (graph 1).

There is a widely held perception that vice does not occur on straw. Veterinary observation confirms this to be erroneous. Figures indicate that whilst a prevalence of 1% of vice is recorded on slatted systems (including part and fully slatted housing) there is still a prevalence of 0.6% on straw based systems - a much lower level but still an important problem (graph 3).

Small differences in the prevalence of vice between batch and continuous flow systems are seen with a similar over representation in indoor derived pigs compared to those for outdoor breeding herds. This latter observation may be confounded by the likelihood of outdoor derived weaners being finished on straw.

Given that, within the main pig keeping areas of East Anglia and North East England, there is a marked difference in the use of straw (graph 3) – it might be expected that East Anglia would demonstrate lower prevalence of vice as a region. This, however, has not been the case over the last year with East Anglia recording a 3-fold prevalence of vice compared to North East England (graph 4). This is the direct result of some very high levels of problems in East Anglia in slatted systems, compared to straw systems (6.5% versus 0.3%).

In North East England, levels of vice seen in straw and slatted systems are equal, but perversely in the Midlands there is more vice on straw! (Graph 5). (The latter observation should be treated with caution as the number of farms is much lower than that of the other 2 regions.)

With respect to unit size, there is no consistent pattern of vice prevalence; the lowest levels are seen in the smallest (<1000) and largest (>8000) sites with more than double the prevalence seen on sites with pig numbers between these two extremes (graph 6).

Finally, the trend of prevalence over a 16-month period is shown in graph 1. The overall levels of vice in 2008 are marginally lower than 2007 and there appear to be troughs in mid-summer and mid-winter, with the suggestion of a peak in autumn and spring, supporting the widely held clinicians’ view that variation in temperature – typical of spring and autumn in UK – may play a part in the occurrence of abhorrent behaviour.

It is pertinent to note that the figures shown are not statistically analysed and are used to show possible association and trends, not definitive fact.