Fig. 1

Graphical illustration of reaction norms for analysis of tolerance. Mean VL is indicated by the stippled line in each graph. Each line corresponds to one of four hypothetical sires. a Null model, where all sires have equal tolerance and equal overall growth level. As such, there is only one (average) tolerance slope. b Reaction-norms of sires with equal tolerance. Sires differ in intercept (growth where VL = 0) and level (growth at mean VL), but have equal tolerance slopes. No re-ranking of sires occurs between growth associated with low and high VL, and genetic correlation between intercept and level is 1.00. c Reaction norms of sires with variation in intercept and tolerance slopes, but no variation in level. Re-ranking of sires occurs depending on whether offspring harbor low or high VL, respectively, as indicated by crossing over of lines before and after mean VL. d Reaction norms of sires where variation occurs at intercept, level and tolerance slope. Sire re-ranking occurs between low and high VL, and genetic correlation between intercept and level is below one