Eighty female pigs were fed, from 25 kg liveweight, either basal diets calculated to provide 32 micrograms available biotin/kg (control diet) or basal diets supplemented with 350 micrograms biotin/kg. Their claws were examined and lesions recorded at 170 days of age and when each of their first four litters was weaned. The incidence of horn 'defects' (superficial bruises, abrasions and cuts in the soft heel) remained at a low level throughout the trial. Neither the number of claws affected with lesions nor the number of lesions per sow differed between treatments at 170 days of age. Between 170 days of age and first weaning the incidence of hoof lesions increased greatly. At first weaning and for the remainder of the trial biotin supplemented sows had significantly fewer claw lesions per sow than controls (P less than 0.05 or greater). The predominant injuries to the foot were cracks which occurred mainly in two associated regions, the heel/toe junction and the heel, and the sidewall and adjacent white-line region of the toe. The differences in foot damage did not result in differences in culling rate. It was concluded that supplemention of the diet of breeding sows with biotin from an early stage of development made a significant contribution to the maintenance of their horn integrity.