Four batches of 60 piglets (males castrated and females) from commercial crossbred pigs (Landrace×Large White)×Duroc) were submitted to the backtest twice during the suckling period, once at 10 days and again at 17 days. The classification of piglets was based on the number of escape attempts (i.e. bouts of struggling with at least the hind legs) made during a restraining period of 60 s. A pig was classified as high-resisting (HR) if it performed more than four escape attempts in the two tests, with a minimum of two attempts per test. If a pig struggled less than four times in two tests, with a maximum of two attempts per test, it was labelled low-resisting (LR) (Bolhuis et al., 2003).