To assess the biotin needs of developing gilts and sows, female swine were fed corn-soybean meal diets supplemented with 0 (NB) or 220 ug (SB) d-biotin/kg diet in three growing-finishing trials and corn (C) or wheat-based (W) diets supplemented with 0 (NB) or 440 (SB) ug d-biotin/kg in a four-parity sow study. During the growing-finishing trials, feedlot performance, hair and soundness scores were unaffected by dietary treatment, however, SB elevated (P<.001) plasma biotin (PB) and reduced the number and frequency of various toe lesions. Conception rate and the weaning to estrus interval were improved (P<.05) with SB. No significant responses were noted in farrowing and lactation performance. There was a trend for SB to improve litter size in multiparous females. Feeding SB diets elevated (P<.001) the biotin content of sow plasma, liver and milk, while sow hepatic pyruvate carboxylase activity was unchanged. Fetal plasma biotin levels were high in pigs from NB females and were increased four-fold when dams received SB diets. Farrowing performance was reduced in W females; however, level of biotin x type of grain interactions were not present. The frequency (%) of females with heel cracks, heel-horn junction cracks and side-wall horn cracks was reduced (P<.01) when females were fed SB diets. Females fed SB diets had fewer (P<.001) total toe lesions, heel cracks, heel-horn junction cracks, side-wall horn cracks and white-line horn cracks (P<.03) compared with NB females. Level of biotin x age interactions (P<.05) indicated that SB was more effective in reducing toe lesions in multiparous females with most reductions occurring following the first parity. Supplemental biotin did not alter soundness scores (P>.10) but increased (P<.001) the number of hairs/cm² and improved (P<.001) hair scores. Toe location influenced toe size and lesion development with outside toes being larger and containing more lesions. Toe lesions and toe size were not correlated (P>.10) to soundness. The results of this study suggest that the development of toe lesions in swine can be reduced with biotin supplementation and improvements in reproductive performance may be attainable. / Doctor of Philosophy