A trailer for treating four-legged animals, comprising: - a floor and a frame which bounds an animal set-up space above said floor, which animal set-up space in top plan view is substantially elongate in a longitudinal direction for taking up and keeping positioned an animal to be treated with a median plane in said longitudinal direction, the frame having a passage opening at a front side of the animal set-up space; - a barrier which is movable between an open position for allowing an animal to pass through the passage opening and a closed position in said passage for preventing an animal from passing through the passage; - a wheel suspension connecting at least two wheels with the frame, each wheel being rotatable about a wheel axle extending perpendicular to a longitudinal direction of the trailer, the wheel suspension being bringable from a drive position in which the frame and the floor is kept above a base or ground and is movable on wheels over it, to an operative position in which the frame rests on the floor surface and the wheels have been moved up with respect to the frame; - a tow bar which is movable sideways relative to the frame and the floor between a central position in which the tow bar in a longitudinal median plane projects forwards with respect to the frame and the floor, and a side position in which at least a front part of the tow bar, with respect to the position of the tow bar in the central position, is moved sideways for, for the purpose of the passing of an animal to or out of the passage, clearing an area in front of said passage opening; characterized in that - the front part of the tow bar which extends beyond the front side of the frame and the floor is pivotable about a horizontal pivot shaft between a swung-down position in which said front part extends substantially in a horizontal plane and a swung-up position in which said front part extends upwardly from said pivot shaft substantially in vertical direction. - a floor and a frame which bounds an animal set-up space above said floor, which animal set-up space in top plan view is substantially elongate in a longitudinal direction for taking up and keeping positioned an animal to be treated with a median plane in said longitudinal direction, the frame having a passage opening at a front side of the animal set-up space; - a barrier which is movable between an open position for allowing an animal to pass through the passage opening and a closed position in said passage for preventing an animal from passing through the passage; - a wheel suspension connecting at least two wheels with the frame, each wheel being rotatable about a wheel axle extending perpendicular to a longitudinal direction of the trailer, the wheel suspension being bringable from a drive position in which the frame and the floor is kept above a base or ground and is movable on wheels over it, to an operative position in which the frame rests on the floor surface and the wheels have been moved up with respect to the frame; - a tow bar which is movable sideways relative to the frame and the floor between a central position in which the tow bar in a longitudinal median plane projects forwards with respect to the frame and the floor, and a side position in which at least a front part of the tow bar, with respect to the position of the tow bar in the central position, is moved sideways for, for the purpose of the passing of an animal to or out of the passage, clearing an area in front of said passage opening; - the front part of the tow bar which extends beyond the front side of the frame and the floor is pivotable about a horizontal pivot shaft between a swung-down position in which said front part extends substantially in a horizontal plane and a swung-up position in which said front part extends upwardly from said pivot shaft substantially in vertical direction.