The effect of rearing regime on mammary gland development and claw abnormalities was assessed using Holstein-Friesian heifers. Treatments included 1) heifers reared to calve at 540 kg and offered grass-silage based diets during the winter and grass-based diets during the summer; 2) heifers reared to calve at 620 kg and offered grass-silage based diets during the winter and grass-based diets during the summer. They also received additional supplements; 3) heifers reared to calve at 620 kg and were offered a straw/concentrate diet during the winter and a grass-based diet during the summer; 4) heifers reared to calve at 620 kg and fed a straw/concentrate diet in both the winter and summer and were housed. By increasing the plane of nutrition, the weight of dissected udder fat increased, but there was no effect on the weight or chemical composition of dissected udder parenchyma. Fat deposition in the udder was reduced and the proportion of parenchyma in the udder was increased by offering straw- compared with silage-based diets. There were no effects on weight of fat when heifers were housed during the first summer and offered straw-based diets compared with those heifers turned out to grass, although there was a tendency towards a reduction in the proportion of parenchyma in the udder. Values for heel height, lateral claw length and heel erosion scores were lower for heifers reared on a low plane of nutrition. A higher plane of nutrition increased live weight/sole area, although it was only significantly higher for treatment 3 compared with treatment 1 heifers. Housing heifers the first summer increased the incidence of feet lesions in the white line and solear area relative to turning heifers out to grass that first summer.