Seasonal trends in ascites from 2010 to 2014 as determined by analysis of a large dataset from the UK broiler flock

In 2007 new EU rules were agreed (Council Directive 2007/43/EC) for the protection of the welfare of broilers, and this ‘Broiler Directive’ came into force in the UK on 30 June 2010. The Directive requires the collection of broiler ‘trigger measures’ at the slaughterhouse and at farm. The data collected is used by to make stocking density (and management) adjustments across the permitted range from 33 to 42 kgm2 in the EU, and up to 39 kgm2 in the UK. This paper reports analysis of ascites incidence derived from the statutory dataset, covering the period 1/7/2010 to 11/5/2014. The data represents cases of ascites detected by post mortem examination at slaughter and of characteristic respiratory pathology and signs of venous congestion and accumulation of tissue fluid. The sample covers 393,474 batches, each batch representing a transporter unit (3,000 to 5,000 birds) arriving at slaughter, and representing overall 2.7 billion birds. The data analysis results in identification of temporal, seasonal and regional trends in the occurrence of ascites. The seasonality of incidence is very apparent, with higher rates in the 1st and 4th period (Autumn/Winter) in each successive year. A discussion of the management factors linked to this seasonal pattern of ascites explores the degree to which this pattern of variation is ‘inherent’ to production systems subject to temperature, humidity and rainfall effects, and how much is dependent on risk factors which derive from the interaction of weather factors with housing, ventilation, temperature control and dust extraction.