Ordinal or visual analogue scales for assessing aspects of broiler chicken welfare?

When the gradation of animal welfare is scored through ordinal scales and equidistant tags are used, empirical data between tags tend to be non-equidistant. Ordinal rate scales (ORS) and visual analogue scales (VAS) were tested for the assessment of contact dermatitis on breast and abdominal areas (CD), footpad dermatitis (FP), hock burns (HB) and bird soiling (BS) in broiler chickens. Calculations regarding the inter-rater reliability, the correlation between VAS and ORS and amongst the welfare indicators measured with both scales, and the equidistance of ORS categories in relation to values measured using VAS, were made. A total of 1,303 broiler chickens from 10 flocks was assessed on-farm by three raters using both scales. Inter-rater reliabilities of CD and HB were higher when using VAS compared with ORS, but FP was lower. Correlations between scales varied between 0.90-0.97 and 0.77-0.95 (P<0.001), considering mean and individual values. Low-to-moderate correlations were observed between the four indicators using the scales. Tags on VAS that best represented ORS were non-equidistant. Results suggest both scales were reliable assessing the selected broiler chicken welfare indicators.