Health-related quality of life (HRQL) was defined for farmed animals and identified as an appropriate focus of integrative welfare measurement for farmed pigs that embraces measurement of positive welfare. The instrument for HRQL measurement was developed specifically for use by farmers and stockpersons, the prime carers of pigs, to increase ownership of welfare improvement amongst those groups. Using a psychometric approach to instrument development, relevant observations were determined by consultation with experienced farmers and stockpersons. These observations included causal variables (cause changes in HRQL) and indicator variables (manifest changes in HRQL). The variables selected as items in the structured questionnaire instrument were those most commonly applied by farmers and stockpersons and also were assigned similar quality-of-life impact by a range of experts including pig veterinary specialists and welfare scientists. The prototype instrument comprises a questionnaire with 98 causal variable items (covering five domains of welfare according with the Five Freedoms) and 30 indicator variable items. It was pre-tested with farmers and stockpersons on commercial farm units and was found to have content (face) validity and high utility. This tool is a novel measure of HRQL in farmed pigs that encompasses the measurement of positive welfare and promotes a move from welfare assurance to welfare enhancement. Further validation of the instrument is described in a companion paper in this issue.

The development of a novel structured questionnaire instrument to measure health-related quality of life (HRQL) in individual farmed pigs was described previously (companion paper). The instrument embraces the measurement of positive welfare, and was developed with farmers and stockpersons, for use by them on-farm. This paper describes the development of a scoring methodology for the instrument and provides evidence for its construct validity. Field testing on four commercial farm units indicated that scores for health and affect correctly allocated 88.7% of pigs to known treatment groups and strongly predicted previously defined intervention levels. The tool was also used in an experimental study alongside other measures to identify the impact of early-life challenges (mixing of pregnant gilts and tail-docking neonatal pigs) on subsequent pig welfare, and identified long-term changes in HRQL of prenatally stressed piglets, a finding supported by other measures. This work describes a novel approach to farm-level welfare assessment in which entirely animal-based HRQL measurement can provide a measure of welfare at the herd level while retaining information about individuals within the herd and about aspects of provision that can be targets of intervention to improve welfare, and promotes a move from welfare assurance to welfare enhancement.