Nucleus populations of Chester White, Duroc, Landrace, and Yorkshire boars and gilts were used to estimate breed differences in temperament and the relationship with performance. Adjusted backfat, adjusted loin depth, days to 113.4 kilograms (DAYS), estimated percent fat-free lean (LEAN), and three temperament scores: load score, scale score, and vocal score were recorded, on a scale of 1 (calm) to 5 (highly excited), during a performance test. Logistic regression for temperament scores included fixed effects of breed, sex, contemporary group (barn-farm-test date), and body weight as a covariate was used. The order that a pig was loaded into the scale, within pen, was included as a fixed effect for load score. After initial analysis, it was determined that vocal score was best described as two categories, vocal or nonvocal, and was reanalyzed accordingly. Linear mixed models for backfat, loin depth, DAYS, and LEAN included fixed effects of breed, sex, and load score, scale score, or vocal score. Growth rate was adjusted to 113.4 kg, while backfat and loin depth were adjusted to 113.4 kg through regression on mean body weight of the respective breed. The odds of increased load score were greater for Landrace than Duroc and Yorkshire respectively. Landrace had a greater probability of a higher scale and vocal scores compared to Chester White, Duroc and Yorkshire. Yorkshire had greater odds of increased load score, scale score, and vocal score than Duroc. Chester White had greater odds of increased load score and scale score than Duroc and Yorkshire, respectively. Chester White were 1.66 times more likely to have a higher vocal scores than Duroc. Phenotypic correlations for scale score with load score, vocal score, backfat, loin depth, DAYS, and LEAN were 0.13, 0.32, −0.15, −0.07, 0.10 and 0.17, respectively. Landrace were more excited and vocal in the scale than Chester White, Durocs and Yorkshire. Landrace were more difficult to load into the scale than Durocs and Yorkshire. Chester White were more active in the scale than Durocs and Yorshire, and more vocal than Durocs. Yorkshire were harder to load, more active and vocal than Durocs. It was concluded that temperament differs between breeds, and pigs with lower temperament scores were fatter, had greater loin depth and grew faster. 

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