The objective was to investigate the effect of sea transport on the physiological, behavioural and performance responses of bulls. One-hundred and eleven bulls (mean body weight (standard error of the mean) 429 (5.7 kg)) were randomly assigned to one of three treatments; control (C; n=54) bulls were housed in 6 pens at Teagasc, Grange Research Centre at a stocking density of (1), 1.7 m(2)/head (C1.7; 3 pens) and (2), 3.4 m(2)/head (C3.4; 3 pens) and (3), transported (T) bulls (n=57) were penned at a space allowance of 1.7 m(2)/head (6 pens) and allocated to one of five decks on the shipping vessel. C and T bulls were subjected to the same live weight (d -2), blood sampling and rectal temperature (d -1) measurements pre-transport and on d 3, d 6, d 9 and d 11 of the study. T bulls had greater (P<0.05) live weight gain (+4.4%) compared with C1.7 bulls (-2.0%) and C3.4 (+0.13%)). Time spent lying was greater (P<0.05) among C1.7 and C3.4 bulls (9.9% and 53.3%, respectively) compared with T bulls (45.8%). Rectal body temperature was not different (P>0.05) among treatment groups throughout the study. At d 11, neutrophil % was greater (P<0.05) in transported bulls on decks 1, 2, 4 and 5 compared with C1.7 and C3.4 treatments. Plasma cortisol concentrations were not different (P>0.05) between control and transported bulls. Plasma creatine kinase (CK) activity was lower (P<0.05) among C3.4 and T bulls on decks 2, 3, 4 and 5 compared with d 3 values. In conclusion, the welfare of bulls transported by sea on the sea journey was not adversely affected. Housing control bulls at a reduced space allowance (1.7 m(2)) had a negative effect on live weight gain.