How to deal with complex data of skin lesions in weaner pigs
Skin lesions of pigs can be used as an indicator of their ability to adapt to the social and physical environment. A total of 315 weaner pigs were assigned to one of three treatments: groups of nine piglets from one litter (9s), mixed groups of nine piglets from three litters (9m) or mixed groups of 36 piglets from four litters (36m). The ear, neck/shoulder, rump, back, hindquarter, tail and belly of piglets were inspected for scratches, abrasions and signs of inflammation on days 0, 5 and 28 post mixing. Due to the large number of body regions, different types of injuries and data from three inspections, the results of explorative data analysis were very heterogeneous. Data preparation focusing on scratches and combination of corresponding regions using factor analysis resulted in a data set which was useful for further statistical procedure. Factor analysis identified corpus, ear and tail as factors. Using the Wilcoxon test different inspections within a treatment were compared. Differences between treatments were analysed using Kruskal-Wallis and Mann-Whitney U tests. Mixed groups (9m, 36m) showed an increase of 'many scratches' on ear and corpus from day 0 to day 5 and a decrease on ear from day 5 to day 28. 'Many scratches' on corpus were more frequent in mixed groups than in single litter groups. This study suggests that skin lesion score can be used to analyse treatment effects on the aggression of pigs. However, it has to be focused on a precise hypothesis and should be based on behavioural observations.
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