Descriptive and temporal analysis of post-mortem lesions recorded in slaughtered pigs in New Zealand from 2000 to 2010.

Aims: To complete a retrospective analysis of data from a national abattoir-based lesion recording system (PigCheck) in the New Zealand pig industry, in order to establish the prevalence of 20 post-mortem disease lesions, describe long-term trends in the prevalence of these lesions, and identify the proportion of the monthly variation in lesion prevalence that could be attributed to individual farms or abattoirs.

Methods: Slaughter lesion data were collected and reported at the lot level (a cohort of pigs delivered from one farm, at one time). Data on the prevalence of lesions between January 2000 and December 2010 was aggregated by month, and time-series analysis of the data for each lesion was conducted. The time series pattern for each lesion was described with an auto-regressive integrated moving average (ARIMA) model; seasonality of lesion occurrence was assessed separately. To determine the proportion of variance in lesion prevalence that could be attributed to farms relative to that attributed to abattoirs, a hierarchical binomial generalised linear mixed model was created incorporating two random effect levels, at the farm (within abattoir) and abattoir levels.

Results: A dataset comprised of 124,407 lots (6,220,664 pigs, 279 farms, five abattoirs) was compiled for analysis. The most prevalent conditions across the 11-year time series were antero-ventral pneumonia (7.6%), pleuropneumonia (11.4%), and milk spots (9.2%). Of the 15 lesions shown to have a significant annual change in prevalence, 10 decreased over time and five increased. The variance in prevalence that was observed for pyogenic lesion (92%), mange (73%), and ileitis (62%) was attributed primarily to variation between abattoirs. By contrast, the farm of origin explained the greatest percentage of variance in prevalence for rectal prolapse (98%), pneumonia (97%), and antero-ventral pneumonia (96%).

Conclusions: The overall prevalence of most lesions recorded in PigCheck for the period was low relative to published data from other countries. Common lung pathologies contributing to lesions such as antero-ventral pneumonia and pleuropneumonia were primarily a function of farm management and were not likely due to variability in lesion recording at different abattoirs.

Clinical Relevance: Based on the low frequency of lesions in pigs at commercial abattoirs, the health status of pigs in the New Zealand pig industry is considered to be very good. Pneumonia, pleurisy, and ascariasis are some of the most prevalent conditions that should be focussed on through development of herd health management plans.