Longitudinal national-level monitoring of on-farm broiler welfare identifies consistently poorly performing farms.

A range of welfare outcome measures relating to on-farm welfare are monitored in UK slaughterhouses to check compliance with the European Broiler Directive. A national dataset from 438,155 batches of chickens between 2010 and 2014 and from 228,795 batches between 2016 and 2018 was analysed. The data contained information about 3.1 billion chickens. The highest mean proportion for a single condition was for ascites/oedema in 2016-2018 at 0.384%, affecting 3.9 million chickens/year sent to slaughter during that time, followed by abnormal colour/fevered at 0.324%, affecting 3.4 million chickens/year. Identifying farms most likely to have poor welfare is an important strategy for improving animal welfare overall, and for maximising the capacity for checking regulatory compliance when resources are limited. We found a greater proportion of broiler farms overall remained consistently in the best quartile (16.4%) rather than the worst quartile (6.6%). Farms that exceeded a Government 'trigger' threshold for poor welfare were significantly more likely to subsequently improve than 'non-trigger' farms, although they usually remained in the worst performing quartile of farms.